U.S. patent number 7,435,810 [Application Number 11/020,428] was granted by the patent office on 2008-10-14 for use of ionic liquids for fabrication of polynucleotide arrays.
This patent grant is currently assigned to Agilent Technologies, Inc.. Invention is credited to Douglas J Dellinger, Geraldine F Dellinger, Joel Myerson, Michel G M Perbost.
United States Patent |
7,435,810 |
Myerson , et al. |
October 14, 2008 |
Use of ionic liquids for fabrication of polynucleotide arrays
Abstract
A method of fabricating polynucleotide arrays includes
dissolving a nucleotide monomer, oligonucleotide, or polynucleotide
in a solvent containing ionic liquid and depositing the resulting
solution on an array substrate. The method has particular
application to fabrication of an addressable array of
polynucleotides on a substrate that carries substrate bound
moieties each with a hydroxyl group. The process may be repeated at
specific locations on the array to elongate the polynucleotide
deposited on the array.
Inventors: |
Myerson; Joel (Berkeley,
CA), Perbost; Michel G M (Bethany, CT), Dellinger;
Douglas J (Boulder, CO), Dellinger; Geraldine F
(Boulder, CO) |
Assignee: |
Agilent Technologies, Inc.
(Santa Clara, CA)
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Family
ID: |
21694110 |
Appl.
No.: |
11/020,428 |
Filed: |
December 22, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050112679 A1 |
May 26, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10001044 |
Oct 31, 2001 |
6852850 |
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Current U.S.
Class: |
536/25.3;
536/23.1; 536/25.33; 536/25.41; 536/25.34; 536/22.1 |
Current CPC
Class: |
B82Y
30/00 (20130101); C07H 21/00 (20130101); B01J
2219/00612 (20130101); C40B 50/14 (20130101); B01J
2219/00378 (20130101); Y02P 20/54 (20151101); B01J
2219/00626 (20130101); C40B 60/14 (20130101); B01J
2219/00675 (20130101); B01J 2219/00677 (20130101); C07B
2200/11 (20130101); B01J 2219/00608 (20130101) |
Current International
Class: |
C07H
21/00 (20060101); C07H 21/02 (20060101); C07H
21/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0742287 |
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Sep 1996 |
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EP |
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WO96/28457 |
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Sep 1996 |
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WO |
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WO98/39348 |
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Mar 1998 |
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WO |
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WO99/54509 |
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Apr 1998 |
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WO |
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WO00/18778 |
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Sep 1998 |
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WO |
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WO00/31/594 |
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Apr 2000 |
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WO |
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Other References
Serge L. Beaucage and Radhakrishnan P. Iyer, "Advances in the
Synthesis of Oligonucleotides by the Phosphoramidite Approach";
Tetrahedron Report No. 309, Vo. 48, No. 12, pp. 2223-2313, 1992.
cited by other .
Ahmad Hasan, Hong Li, Jeno Toamsz and Barbara Ramsay Shaw; "
Base-boronated Dinucleotides: synthesis and effect of
N7-cyanoborane substitution on the base protons"; Nucleic Acids
Research, 1996 vol. 24, No. 11; pp. 2150-2157. cited by other .
Frank Bergman, Erich Kueng, Patrick Iaiza, and Willi Bannwarth;
Allyl as Internucleotide Protecting Group in DNA Synthesis to be
cleaved off by Ammonia; Tetrahedron, vol. 51, No. 25, 99.
6971-6976, 1995. cited by other .
Frank Bergman and Wolfgang Pfleiderer; "Nucleotides"; The
2-Dansylethoxycarbonyl
(=2-{[5-(Dimethylamino)napththalen-1-yl]sulfonyl} ethoxcarbonyl;
Dnseoc) Group for Protection of the 5'-Hydroxy Function in
Ologodeoxyribonucleotide Synethesis; Helvetica Chimica Acta--vol.
77(1994); pp. 203-213. cited by other .
Michael C. Pirrung and Lora Fallon; Glenn McGall "Proofing of
Photolithographic DNA Synthesis with 3',
5'--Dimethoxybenzoinyloxycarbonyl-Protected Doxynucleoside
Phosphoramidites"; 1998 American Chemical Society, pp. 241-246.
cited by other .
Haraold Sigmund, Thomas Maier and Wolfgang Pfeiderer; A New Type of
Fluorescence Labeling of Nucleosides Nucleotides and
Oligonucleotides:; Nucleosides & Nucleotides, 16(5&6), pp.
685-696 (1997). cited by other .
Glenn H. McGall, Anthony D. Barone, Martin Diggelman, Stephen P. A.
Fodor, Erik Gentalen, and Nam Ngo; "The Efficiency of
Light-Directed Synthesis of DNA Arrays on Glass Substrates";
Journal of the American Chemical Society, vol. 119, No. 22, Jun. 4,
1997, pp. 5081-5090. cited by other .
Michael C. Pirrung and Jean Claude-Bradley; "Comparison of Methods
for Photochemical Phosphoramidite-Based DNA Synthesis", J. Org.
Chem. 1995, vol. 60, pp. 6270-6276. cited by other .
Hayes Dougan, John B. Hobbs, Jeffrey I. Weitz and Donald M. Lyster;
"Sunthesis and Raioiodination of a Stannyl
Oligofeoxyribonucleotide"; Nucleic Acids Research, 1997, vol. 25,
No. 14, pp. 2897-2901. cited by other .
Shegenori Iwai and Eiko Ohtsuka; "t'-Levulinyl and
2-tetrahydrofuranyl protection for the synthesis of
oligoribonucleotides by the Phosphoramidite approach"; Nucleic
Acids Research, vol. 16, No. 20, 1988. cited by other .
Earle et al., "Ionic Liquids, Green solvents for the future", Pure
Applied Chemistry, vol. 72, No. 7, pp. 1391-1398, 2000. cited by
other .
Earle et al., Paradigm Confirmed: The First Ude of Ionic Liquids to
Dramatically Influence the Outcome of Chemical Reactions Organic
Letters, vol. 6, No. 5, pp. 707-710, 2004. cited by other.
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Primary Examiner: Jiang; Shaojia Anna
Assistant Examiner: McIntosh, III; Traviss C
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to and is a continuation of U.S.
application entitled, "Use of Ionic Liquids for Fabrication of
Polynucleotide Arrays", Ser. No. 10/001,044, filed Oct. 31, 2001,
now U.S. Pat. No. 6,852,850, which is entirely incorporated herein
by reference. This application relates to a U.S. Patent Application
entitled "Method of Synthesizing Polynucleotides Using Ionic
Liquids," having Ser. No. 09/999,623, filed Oct. 31, 2001, now U.S.
Pat. No. 6,858,720, which is entirely incorporated herein by
reference.
Claims
What is claimed is:
1. A method of immobilizing a nucleotide monomer, oligonucleotide,
or polynucleotide upon an insoluble substrate, the method
comprising a) dissolving a nucleotide monomer, oligonucleotide, or
polynucleotide in a solvent comprising an ionic liquid such that
the resulting solution comprises at least 50% by weight ionic
liquid, and b) contacting the insoluble substrate with the solution
resulting from a) under conditions and for a time sufficient to
immobilize the nucleotide monomer, oligonucleotide, or
polynucleotide upon the insoluble substrate.
2. The method of claim 1 wherein the solution includes at least
about 75% by weight of an ionic liquid.
3. The method of claim 1 wherein the solution includes at least
about 90% by weight of an ionic liquid.
4. The method of claim 1 wherein the solution includes at least
about 98% by weight of an ionic liquid.
5. The method of claim 1 wherein the ionic liquid is an organic
salt comprising a substituted heterocyclic organic cation.
6. The method of claim 5 wherein the ionic liquid is an organic
salt comprising a cation selected from an N-substituted pyridine
and a 1,3-disubstituted imidazole.
7. The method of claim 5 wherein the organic salt comprises an
anion selected from chloride (Cl.sup.-), bromide (Br.sup.-),
tetrafluoroborate ([BF.sub.4].sup.-), hexafluorophosphate
([PF.sub.6].sup.-), [SbF.sub.6].sup.-, [CuCl.sub.2].sup.-,
[AlCl.sub.4].sup.-, [Al.sub.2Cl.sub.7].sup.-,
[Al.sub.3Cl.sub.10].sup.-, methylsulfate (CH.sub.3SO.sub.4.sup.-),
trifluoroacetate (CF.sub.3CO.sub.2.sup.-), heptafluorobutanoate
(CF.sub.3(CF.sub.2).sub.2CO.sub.2.sup.-), triflate
(CF.sub.3SO.sub.2.sup.-), nonaflate (C.sub.2F.sub.5SO.sub.2.sup.-),
bis(trifluoromethylsulfonyl)imide
((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide
((C.sub.2F.sub.5SO.sub.2).sub.2N.sup.-), and
tris(trifluoromethylsulfonyl)methide
((CF.sub.3SO.sub.2).sub.3C.sup.-).
8. The method of claim 5 wherein the organic salt is characterized
as being a liquid when being >98% pure and at standard
temperature and pressure.
9. The method of claim 5 wherein the organic salt is characterized
as being a liquid below about 80.degree. C. at about standard
atmospheric pressure.
10. The method of claim 5 wherein the cation is an N-substituted
pyridine having the formula ##STR00006## wherein R is alkyl and
each R' is independently selected from hyrido, alkyl, or halogen
group.
11. The method of claim 5 wherein the cation has the formula
##STR00007## wherein each R is independently selected from alkyl,
each R' is independently selected from hydrido, alkyl, or halogen,
and R'' is selected from hydrido or methyl.
12. The method of claim 1 further comprising conducting steps a)
and b) at each of a plurality of sites on the insoluble substrate
to form an addressable array of polynucleotides on the insoluble
substrate.
13. The method of claim 1 wherein the contacting is performed by
depositing droplets of the solution resulting from a) on the
substrate using an ink jet device.
14. A method of forming a bond between a reactive group immobilized
on an insoluble substrate and a molecule selected from the group
consisting of a nucleotide monomer, an olignucleotide, and a
polynucleotide; the method comprising contacting the reactive group
with a solution comprising the molecule and at least 50% by weight
of an ionic liquid ionic liquid.
15. The method of claim 14 wherein the solution includes at least
about 75% by weight of an ionic liquid.
16. The method of claim 14 wherein the solution includes at least
about 90% by weight of an ionic liquid.
17. The method of claim 14 wherein the solution includes at least
about 98% by weight of an ionic liquid.
18. The method of claim 14 wherein the bond is an internucleotide
bond.
19. The method of claim 18, further comprising contacting the
internucleotide bond with an oxidizing reagent to oxidize the
internucleotide bond.
20. The method of claim 19 wherein the insoluble substrate is a
planar substrate having a surface, an array of polynucleotides
being arranged upon the surface.
21. The method of claim 14 wherein the ionic liquid is an organic
salt comprising a substituted heterocyclic organic cation.
22. The method of claim 14 wherein the ionic liquid is an organic
salt comprising a cation selected from an N-substituted pyridine
and a 1,3-disubstituted imidazole.
23. The method of claim 21, the organic salt comprising an anion
selected from chloride (Cl.sup.-), bromide (Br.sup.-),
tetrafluoroborate ([BF.sub.4].sup.-), hexafluorophosphate
([PF.sub.6].sup.-), [SbF.sub.6].sup.-, [CuCl.sub.2].sup.-,
[AlCl.sub.4].sup.-, [Al.sub.2Cl.sub.7].sup.-,
[Al.sub.3Cl.sub.10].sup.-, methylsulfate (CH.sub.3SO.sub.4.sup.-),
trifluoroacetate (CF.sub.3CO.sub.2.sup.-), heptafluorobutanoate
(CF.sub.3(CF.sub.2).sub.2CO.sub.2.sup.-), triflate
(CF.sub.3SO.sub.2.sup.-), nonaflate (C.sub.2F.sub.5SO.sub.2.sup.-),
bis(trifluoromethylsulfonyl)imide
((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide
((C.sub.2F.sub.5SO.sub.2).sub.2N.sup.-), and
tris(trifluoromethylsulfonyl)methide
((CF.sub.3SO.sub.2).sub.3C.sup.-).
24. The method of claim 14, the organic salt having the
characteristic of being a liquid when being >98% pure and at
standard temperature and pressure.
25. The method of claim 21 wherein the cation is an N-substituted
pyridine having the formula ##STR00008## wherein R is alkyl and
each R' is independently selected from hyrido, alkyl or halogen
group.
26. The method of claim 21 wherein the cation has the formula
##STR00009## wherein each R is independently selected from alkyl,
each R' is independently selected from hydrido, alkyl, or halogen,
and R'' is selected from hydrido or methyl.
27. The method of claim 14 wherein the contacting is performed by
depositing droplets of the solution on the substrate using an ink
jet device.
28. The method of claim 14 wherein the organic salt is
characterized as being a liquid below about 80.degree. C. at about
standard atmospheric pressure.
Description
DESCRIPTION
1. Field of the Invention
The invention relates generally to methods of forming arrays of
polynucleotides on planar surfaces. The invention more specifically
relates to depositing a composition that includes an ionic liquid
and appropriate nucleotide monomers, oligonucleotides, or
polynucleotides upon a planar surface to chemically bond the
monomers, oligonucleotides, or polynucleotides to the planar
surface.
2. Background of the Invention
Oligonucleotides or polynucleotides immobilized on planar
substrates are increasingly useful as diagnostic or screening
tools. Polynucleotide arrays include regions of usually different
sequence oligonucleotides or polynucleotides arranged in a
predetermined configuration on the substrate. These regions
(sometimes referenced as "features") are positioned at respective
locations ("addresses") on the substrate. The arrays, when exposed
to a sample, will exhibit an observed binding pattern. This binding
pattern can be detected upon interrogating the array. For example,
all polynucleotide targets (e.g. DNA) in the sample can be labeled
with a suitable label (such as a fluorescent compound), and the
fluorescence pattern on the array accurately observed following
exposure to the sample. Assuming that the different sequence
polynucleotides were correctly deposited in accordance with the
predetermined configuration, then the observed binding pattern will
be indicative of the presence and/or concentration of one or more
polynucleotide components of the sample.
Polynucleotide arrays can be fabricated by depositing previously
obtained polynucleotides onto a substrate, or by in situ synthesis
methods. Various chemical schemes have been described for the
synthesis of polynucleotides. Typically these methods use a
nucleoside reagent of the formula:
##STR00001## in which:
A represents H or an optionally protected hydroxyl group;
B is a purine or pyrimidine base whose exocyclic amine functional
group is optionally protected;
one of M or Q is a conventional protecting group for the 3' or
5'-OH functional group (or, optionally, a conventional 3' or 5'-OH
protecting group at the end of an intervening (and optionally
protected) polynucleotide sequence, e.g. such that eq. (I) can
represent a modified polynucleotide) while the other is:
##STR00002##
where x may be 0 or 1, provided that:
a) when x=1:
R' represents H and R'' represents a negatively charged oxygen
atom; or
R' is an oxygen atom and R'' represents either an oxygen atom or an
oxygen atom carrying a protecting group; and
b) when x=0, R' is an oxygen atom carrying a protecting group and
R'' is either a hydrogen or a di-substituted amine group.
When x is equal to 1, R' is an oxygen atom and R'' is an oxygen
atom, the method is in this case the so-called phosphodiester
method; when R'' is an oxygen atom carrying a protecting group, the
method is in this case the so-called phosphotriester method.
When x is equal to 1, R' is a hydrogen atom and R'' is a negatively
charged oxygen atom, the method is known as the H-phosphonate
method.
When x is equal to 0, R' is an oxygen atom carrying a protecting
group and R'' is a halogen, the method is known as the phosphite
method, and when R'' is a leaving group of the disubstituted amine
type, the method is known as the phosphoramidite method.
The conventional sequence used to prepare an oligonucleotide using
reagents of the type of formula (I), basically follows four
separate steps: (a) coupling a selected nucleoside which also has a
protected hydroxy group, through a phosphite linkage to a
functionalized support in the first iteration, or a nucleoside
bound to the substrate (i.e. the nucleoside-modified substrate) in
subsequent iterations; (b) optionally, but preferably, blocking
unreacted hydroxyl groups on the substrate bound nucleoside; (c)
oxidizing the phosphite linkage of step (a) to form a phosphate
linkage; and (d) removing the protecting group ("deprotection")
from the now substrate bound nucleoside coupled in step (a), to
generate a reactive site for the next cycle of these steps. The
functionalized support (in the first cycle) or deprotected coupled
nucleoside (in subsequent cycles) provides a substrate bound moiety
with a linking group for forming the phosphite linkage with a next
nucleoside to be coupled in step (a). Final deprotection of
nucleoside bases can be accomplished using alkaline conditions such
as ammonium hydroxide, in a known manner.
The in situ method for fabricating a polynucleotide array typically
follows, at each of the multiple different addresses at which
features are to be formed, the same conventional iterative sequence
used in forming polynucleotides on a support by means of known
chemistry. During array fabrication, different monomers may be
deposited at different addresses on the substrate during any one
iteration so that the different features of the completed array
will have different desired polynucleotide sequences. The coupling
can be performed by depositing drops of an activator and
phosphoramidite at the specific desired feature locations for the
array. One or more intermediate further steps may be required in
each iteration, such as the conventional oxidation and washing
steps.
Methods of depositing materials onto a planar substrate include
loading and then touching a pin or capillary to a surface, such as
described in U.S. Pat. No. 5,807,522, or deposition by firing from
a pulse jet such as an inkjet head, such as described in PCT
publications WO 95/25116 and WO 98/41531 and in U.S. Pat. No.
6,180,351, and elsewhere. For in situ fabrication methods, multiple
different reagent droplets are deposited by pulse jet or other
means at a given target location in order to form the final feature
(hence a probe of the feature is synthesized on the array
substrate). Some protocols flood the substrate with reagent
solutions during one or more steps of the cycle, e.g. deprotection,
oxidation, or washing steps.
The foregoing methods of preparing polynucleotides are well known
and described in detail, for example, in Caruthers, Science 230:
281-285, 1985; Itakura et al., Ann. Rev. Biochem. 53: 323-356;
Hunkapillar et al., Nature 310: 105-110, 1984; and in "Synthesis of
Oligonucleotide Derivatives in Design and Targeted Reaction of
Oligonucleotide Derivatives, CRC Press, Boca Raton, Fla., pages 100
et seq., U.S. Pat. No. 4,415,732, U.S. Pat. No. 4,458,066, U.S.
Pat. No. 4,500,707, U.S. Pat. No. 5,153,319, U.S. Pat. No.
5,869,643, EP 0294196, and elsewhere. The phosphoramidite and
phosphite triester approaches are most broadly used, but other
approaches include the phosphodiester approach, the phosphotriester
approach and the H-phosphonate approach. Such approaches are
described in Beaucage et al., Tetrahedron (1992) 12:2223-2311. A
more recent approach for synthesis of polynucleotides is described
in U.S. Pat. No. 6,222,030 B1 to Dellinger et al., issued Apr. 24,
2001.
In the typical phosphoramidite method of solid phase
oligonucleotide synthesis, the synthesis typically proceeds in the
3' to 5' direction (referring to the sugar component of the added
nucleoside), although the synthesis may easily be conducted in the
reverse direction. The added nucleoside generally has a
dimethoxytrityl protecting group on its 5' hydroxyl and a
phosphoramidite functionality on its 3' hydroxyl position. Beaucage
et al. (1981) Tetrahedron Lett. 22:1859. See FIG. 1 for a schematic
representation of this technology. In FIG. 1 "B" represents a
purine or pyrimidine base, "DMT" represents dimethoxytrityl
protecting group and "iPr" represents isopropyl. In the first step
of the synthesis cycle, the "coupling" step, the 5' end of the
growing chain is coupled with the 3' phosphoramidite of the
incoming monomer to form a phosphite triester intermediate (the 5'
hydroxyl protecting group prevents more than one monomer per
synthesis cycle from attaching to the growing chain). Matteucci et
al. (1981) J. Am. Chem. Soc. 103:3185. Next, the optional "capping
reaction" is used to stop the synthesis on any chains having an
unreacted 5' hydroxyl, which would be one nucleotide short at the
end of synthesis. The phosphite triester intermediate is subjected
to oxidation (the "oxidation" step) after each coupling reaction to
yield a more stable phosphotriester intermediate. Without
oxidation, the unstable phosphite triester linkage would cleave
under the acidic conditions of subsequent synthesis steps.
Letsinger et al. (1976) J. Am. Chem. Soc. 98:3655. Removal of the
5' protecting group of the newly added monomer (the "deprotection"
step) is typically accomplished by reaction with acidic solution to
yield a free 5' hydroxyl group, which can be coupled to the next
protected nucleoside phosphoramidite. This process is repeated for
each monomer added until the desired sequence is synthesized. A
final deprotection step is provided in which nitrogenous bases and
phosphate group are simultaneously deprotected by treatment with
ammonium hydroxide and/or methylamine under known conditions.
According to some protocols, the synthesis cycle of couple, cap,
oxidize, and deprotect is shortened by omitting the capping step or
by taking the oxidation step `outside` of the cycle and performing
a single oxidation reaction on the completed chain. For example,
oligonucleotide synthesis according to H-phosphonate protocols will
permit a single oxidation step at the conclusion of the synthesis
cycles. However, coupling yields are less efficient than those for
phosphoramidite chemistry and oxidation requires longer times and
harsher reagents than amidite chemistry.
Conventional synthesis protocols of oligonucleotides are not
without disadvantages. For example, cleavage of the DMT protecting
group under acidic conditions gives rise to the
resonance-stabilized and long-lived bis(p-anisyl)phenylmethyl
carbocation. Gilham et al. (1959) J. Am. Chem. Soc. 81:4647.
Protection and deprotection of hydroxyl groups with DMT are thus
readily reversible reactions, resulting in side reactions during
oligonucleotide synthesis and a lower yield than might otherwise be
obtained. To circumvent such problems, large excesses of acid are
used with DMT to achieve quantitative deprotection. The excess acid
leads to the acid-catalyzed depurination of the oligonucleotides,
thus impairing the synthesis. Caruthers et al., in Genetic
Engineering: Principles and Methods, J. K. Setlow et al., Eds. (New
York: Plenum Press, 1982).
Applications in the field of genomics and high throughput screening
have fueled the demand for increased performance of analytical
systems that use polynucleotide arrays. Thus, the arrays need to be
fabricated with very small, densely packed features, increasing the
need for very precise chemistry in such a context. Smearing or
streaking of features becomes more problematice at small scales, as
does undesirable hydrolysis of reagents. In particular, the
reagents used in the coupling step typically are highly susceptible
to hydrolysis. As feature size becomes smaller, the efficiency of
the coupling reaction goes down because of increasing hydrolysis.
The use of dry solvents and dry atmosphere for the synthesis has
resulted in limited success at a greater cost.
The problems associated with the use of DMT are exacerbated in
polynucleotide array synthesis where "microscale" parallel
reactions are taking place on a very dense, packed surface. Thus,
increasingly stringent demands are placed on the chemical synthesis
cycle as it was originally conceived, and the problems associated
with conventional methods for synthesizing oligonucleotides are
rising to unacceptable levels in these expanded applications.
Salts that are fluid at room temperature have been investigated as
environmentally friendly solvents. These salts have been termed
`room temperature ionic liquids` (herein simply referred to as
`ionic liquids`) and are generally composed of a heterocyclic
cation, e.g. a substituted imidazole or pyridine, and an anion such
as tetrafluoroborate or hexafluorophosphate, although certain
organic anions such as methylsulfate (CH.sub.3SO.sub.4.sup.-),
among others, have been discovered to be effective as the anion in
certain organic liquids. Ionic liquids are known to dissolve a wide
range of substances, both organic and inorganic. Ionic liquids
typically are non-corrosive, have little or no vapor pressure under
standard conditions, and exhibit low viscosity. More information
regarding ionic liquids may be gleaned from two review articles by
Hussey (Hussey, C. L., Adv. Molten Salt Chem. (1983) 5:185; and
Hussey, C. L., Pure Appl. Chem. (1988) 60:1763).
SUMMARY OF THE INVENTION
The invention is thus addressed to the aforementioned deficiencies
in the art, and provides novel methods for fabricating
polynucleotide arrays, wherein the methods have numerous advantages
relative to prior methods such as those discussed above. The
methods involve a process of immobilizing a nucleotide monomer,
oligonucleotide, or polynucleotide upon an insoluble substrate in
the presence of an ionic liquid. The present invention provides a
method of generating an addressable array of polynucleotides on a
substrate. This method includes dissolving a nucleotide monomer,
oligonucleotide, or polynucleotide in a solvent comprising an ionic
liquid. An array substrate is then contacted with the resulting
solution. The substrate has a surface reactive group which, when
contacted with the resulting solution, reacts to covalently bind
the nucleotide monomer, oligonucleotide, or polynucleotide to the
substrate.
The invention encompasses a method for the formation of a bond
between (a) a nucleotide monomer, olignucleotide or polynucleotide
dissolved in a solvent comprising an ionic liquid, and (b) a
reactive group on a substrate, where the reactive group may be a
part of an immobilized nucleotide monomer, an immobilized
oligonucleotide, or an immobilized polynucleotide, or the reactive
group may be a part of the planar substrate base material or a
surface modification of the base material. The formation of the
bond thus results in the dissolved nucleotide monomer,
olignucleotide or polynucleotide being immobilized to the planar
substrate surface via the bond and via any immobilized
oligonucleotide or polynucleotide previously immobilized on the
surface.
The compositions and methods described are particularly useful for
fabricating an addressable polynucleotide array by in situ
synthesis of polynucleotides on the array substrate. In one such
embodiment, at each of the multiple different addresses on the
substrate (for example, at least one hundred, at least one
thousand, or at least ten thousand addresses), the in situ
synthesis cycle is repeated so as to form the addressable array
with different polynucleotide sequences at different addresses. In
the array forming method, the nucleosides to be coupled at
respective addresses are dissolved in a solvent containing ionic
liquid and deposited as droplets at those addresses.
Additional objects, advantages, and novel features of this
invention shall be set forth in part in the descriptions and
examples that follow and in part will become apparent to those
skilled in the art upon examination of the following specifications
or may be learned by the practice of the invention. The objects and
advantages of the invention may be realized and attained by means
of the instruments, combinations, compositions and methods
particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will be understood from
the description of representative embodiments of the method herein
and the disclosure of illustrative apparatus for carrying out the
method, taken together with the Figures, wherein
FIG. 1 schematically illustrates a prior art oligonucleotide
synthesis method using phosphoramidite monomers. The known prior
art methods, including the one illustrated, do not describe the use
of ionic liquids in the coupling step where the internucleotide
bond is formed.
FIG. 2 depicts a substrate bearing multiple arrays, as may be
produced as described herein.
FIG. 3 is an enlarged view of a portion of FIG. 2 showing some of
the identifiable individual regions (spots, or features) of a
single array of FIG. 2.
FIG. 4 shows components of an apparatus useful in fabricating
polynucleotide arrays according to the present invention.
To facilitate understanding, identical reference numerals have been
used, where practical, to designate corresponding elements that are
common to the Figures. Figure components are not drawn to
scale.
DETAILED DESCRIPTION
Before the invention is described in detail, it is to be understood
that unless otherwise indicated this invention is not limited to
particular materials, reagents, reaction materials, manufacturing
processes, or the like, as such may vary. It is also to be
understood that the terminology used herein is for purposes of
describing particular embodiments only, and is not intended to be
limiting. It is also possible in the present invention that steps
may be executed in different sequence where this is logically
possible. However, the sequence described below is preferred.
It must be noted that, as used in the specification and the
appended claims, the singular forms "a," "an" and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "an insoluble support" includes a
plurality of insoluble supports. In this specification and in the
claims that follow, reference will be made to a number of terms
that shall be defined to have the following meanings unless a
contrary intention is apparent:
As used herein, polynucleotides include single or multiple stranded
configurations, where one or more of the strands may or may not be
completely aligned with another. The terms "polynucleotide" and
"oligonucleotide" shall be generic to polydeoxynucleotides
(containing 2-deoxy-D-ribose), to polyribonucleotides (containing
D-ribose), to any other type of polynucleotide which is an
N-glycoside of a purine or pyrimidine base, and to other polymers
in which the conventional backbone has been replaced with a
non-naturally occurring or synthetic backbone or in which one or
more of the conventional bases has been replaced with a
non-naturally occurring or synthetic base.
A "nucleotide" refers to a sub-unit of a nucleic acid (whether DNA
or RNA or analogue thereof) which includes a phosphate group, a
sugar group and a nitrogen containing base, as well as analogs of
such sub-units. A "nucleoside" references a nucleic acid subunit
including a sugar group and a nitrogen containing base. A
"nucleoside moiety" refers to a molecule having a sugar group and a
nitrogen containing base (as in a nucleoside) as a portion of a
larger molecule, such as in a polynucleotide, oligonucleotide, or
nucleoside phosphoramidite. A "nucleotide monomer" refers to a
molecule which is not incorporated in a larger oligo- or
poly-nucleotide chain and which corresponds to a single nucleotide
sub-unit; nucleotide monomers may also have activating or
protecting groups, if such groups are necessary for the intended
use of the nucleotide monomer. A "polynucleotide intermediate"
references a molecule occurring between steps in chemical synthesis
of a polynucleotide, where the polynucleotide intermediate is
subjected to further reactions to get the intended final product,
e.g. a phosphite intermediate which is oxidized to a phosphate in a
later step in the synthesis, or a protected polynucleotide which is
then deprotected. An "oligonucleotide" generally refers to a
nucleotide multimer of about 2 to 100 nucleotides in length, while
a "polynucleotide" includes a nucleotide multimer having any number
of nucleotides. It will be appreciated that, as used herein, the
terms "nucleoside" and "nucleotide" will include those moieties
which contain not only the naturally occurring purine and
pyrimidine bases, e.g., adenine (A), thymine (T), cytosine (C),
guanine (G), or uracil (U), but also modified purine and pyrimidine
bases and other heterocyclic bases which have been modified (these
moieties are sometimes referred to herein, collectively, as "purine
and pyrimidine bases and analogs thereof"). Such modifications
include, e.g., methylated purines or pyrimidines, acylated purines
or pyrimidines, and the like, or the addition of a protecting group
such as acetyl, difluoroacetyl, trifluoroacetyl, isobutyryl,
benzoyl, or the like. The purine or pyrimidine base may also be an
analog of the foregoing; suitable analogs will be known to those
skilled in the art and are described in the pertinent texts and
literature. Common analogs include, but are not limited to,
1-methyladenine, 2-methyladenine, N6-methyladenine,
N6-isopentyladenine, 2-methylthio-N6-isopentyladenine,
N,N-dimethyladenine, 8-bromoadenine, 2-thiocytosine,
3-methylcytosine, 5-methylcytosine, 5-ethylcytosine,
4-acetylcytosine, 1-methylguanine, 2-methylguanine,
7-methylguanine, 2,2-dimethylguanine, 8-bromoguanine,
8-chloroguanine, 8-aminoguanine, 8-methylguanine, 8-thioguanine,
5-fluorouracil, 5-bromouracil, 5-chlorouracil, 5-iodouracil,
5-ethyluracil, 5-propyluracil, 5-methoxyuracil,
5-hydroxymethyluracil, 5-(carboxyhydroxymethyl)uracil,
5-(methylaminomethyl)uracil, 5-(carboxymethylaminomethyl)-uracil,
2-thiouracil, 5-methyl-2-thiouracil, 5-(2-bromovinyl)uracil,
uracil-5-oxyacetic acid, uracil-5-oxyacetic acid methyl ester,
pseudouracil, 1-methylpseudouracil, queosine, inosine,
1-methylinosine, hypoxanthine, xanthine, 2-aminopurine,
6-hydroxyaminopurine, 6-thiopurine and 2,6-diaminopurine.
An "internucleotide bond" refers to a chemical linkage between two
nucleoside moieties, such as a phosphodiester linkage in nucleic
acids found in nature, or such as linkages well known from the art
of synthesis of nucleic acids and nucleic acid analogues. An
internucleotide bond may comprise a phospho or phosphite group, and
may include linkages where one or more oxygen atoms of the phospho
or phosphite group are either modified with a substituent or
replaced with another atom, e.g. a sulfur atom, or the nitrogen
atom of a mono- or di-alkyl amino group.
An "array", unless a contrary intention appears, includes any one,
two or three dimensional arrangement of addressable regions bearing
a particular chemical moiety or moieties (for example,
polynucleotide sequences) associated with that region. An array is
"addressable" in that it has multiple regions of different moieties
(for example, different polynucleotide sequences) such that a
region (a "feature" or "spot" of the array) at a particular
predetermined location (an "address") on the array will detect a
particular target or class of targets (although a feature may
incidentally detect non-targets of that feature). In the case of an
array, the "target" will be referenced as a moiety in a mobile
phase (typically fluid), to be detected by probes ("target probes")
which are bound to the substrate at the various regions. However,
either of the "target" or "target probes" may be the one which is
to be evaluated by the other (thus, either one could be an unknown
mixture of polynucleotides to be evaluated by binding with the
other). While probes and targets of the present invention will
typically be single-stranded, this is not essential. An "array
layout" refers to one or more characteristics of the array, such as
feature positioning, feature size, and some indication of a moiety
at a given location. "Hybridizing" and "binding", with respect to
polynucleotides, are used interchangeably.
A "group" includes both substituted and unsubstituted forms.
Typical substituents include one or more lower alkyl, any halogen,
hydroxy, or aryl, or optionally substituted on one or more
available carbon atoms with a nonhydrocarbyl substituent such as
cyano, nitro, halogen, hydroxyl, or the like. Any substituents are
typically chosen so as not to substantially adversely affect
reaction yield (for example, not lower it by more than 20% (or 10%,
or 5% or 1%) of the yield otherwise obtained without a particular
substituent or substituent combination). An "acetic acid" includes
substituted acetic acids such as di-chloroacetic acid (DCA) or
tri-chloroacetic acid (TCA).
A "phospho" group includes a phosphodiester, phosphotriester, and
H-phosphonate groups. In the case of either a phospho or phosphite
group, a chemical moiety other than a substituted 5-membered furyl
ring may be attached to O of the phospho or phosphite group which
links between the furyl ring and the P atom.
A "protecting group" is used in the conventional chemical sense to
reference a group which reversibly renders unreactive a functional
group under specified conditions of a desired reaction. After the
desired reaction, protecting groups may be removed to deprotect the
protected functional group. All protecting groups should be
removable (and hence, labile) under conditions which do not degrade
a substantial proportion of the molecules being synthesized. In
contrast to a protecting group, a "capping group" permanently binds
to a segment of a molecule to prevent any further chemical
transformation of that segment. A "hydroxyl protecting group"
refers to a protecting group where the protected group is a
hydroxyl. A "reactive-site hydroxyl" is the terminal 5'-hydroxyl
during 3'-5' polynucleotide synthesis and is the 3'-hydroxyl during
5'-3' polynucleotide synthesis. An "acid labile protected hydroxyl"
is a hydroxyl group protected by a protecting group that can be
removed by acidic conditions. Similarly, an "acid labile protecting
group" is a protecting group that can be removed by acidic
conditions. Preferred protecting groups that are capable of removal
under acidic conditions ("acid-labile protecting groups") include
those such as tetrahydropyranyl groups, e.g. tetrahydropyran-2-yl
and 4-methoxytetrahydropyran-2-yl; an arylmethyl group with n aryl
groups (where n=1 to 3) and 3-n alkyl groups such as an optionally
substituted trityl group, for example a monomethoxytrityl for
oligoribonucleotide synthesis and a dimethoxytrityl for
oligodeoxyribonucleotide synthesis, pixyl; isobutyloxycarbonyl;
t-butyl; and dimethylsilyl. A trityl group is a triphenylmethyl
group. Suitable protecting groups are described in "Protective
Groups in Organic Synthesis" by T. W. Green, Wiley
Interscience.
The term "alkyl" as used herein, unless otherwise specified, refers
to a saturated straight chain, branched or cyclic hydrocarbon group
of 1 to 24, typically 1-12, carbon atoms, such as methyl, ethyl,
n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl,
cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl,
3-methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl. The term
"lower alkyl" intends an alkyl group of one to eight carbon atoms,
and includes, for example, methyl, ethyl, ni-propyl, isopropyl,
n-butyl, isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl,
neopentyl, hexyl, isohexyl, cyclohexyl, 3-methylpentyl,
2,2-dimethylbutyl, and 2,3-dimethylbutyl. The term "cycloalkyl"
refers to cyclic alkyl groups such as cyclopropyl, cyclobutyl,
cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.
The term "alkenyl" as used herein, unless otherwise specified,
refers to a branched, unbranched or cyclic (in the case of C5 and
C6) hydrocarbon group of 2 to 24, typically 2 to 12, carbon atoms
containing at least one double bond, such as ethenyl, vinyl, allyl,
octenyl, decenyl, and the like. The term "lower alkenyl" intends an
alkenyl group of two to eight carbon atoms, and specifically
includes vinyl and allyl. The term "cycloalkenyl" refers to cyclic
alkenyl groups.
The term "alkynyl" as used herein, unless otherwise specified,
refers to a branched or unbranched hydrocarbon group of 2 to 24,
typically 2 to 12, carbon atoms containing at least one triple
bond, such as acetylenyl, ethynyl, n-propynyl, isopropynyl,
n-butynyl, isobutynyl, t-butynyl, octynyl, decynyl and the like.
The term "lower alkynyl" intends an alkynyl group of two to eight
carbon atoms, and includes, for example, acetylenyl and propynyl,
and the term "cycloalkynyl" refers to cyclic alkynyl groups.
The term "aryl" as used herein refers to an aromatic species
containing 1 to 5 aromatic rings, either fused or linked, and
either unsubstituted or substituted with 1 or more substituents
typically selected from the group consisting of amino, halogen and
lower alkyl. Preferred aryl substituents contain 1 to 3 fused
aromatic rings, and particularly preferred aryl substituents
contain 1 aromatic ring or 2 fused aromatic rings. Aromatic groups
herein may or may not be heterocyclic. The term "aralkyl" intends a
moiety containing both alkyl and aryl species, typically containing
less than about 24 carbon atoms, and more typically less than about
12 carbon atoms in the alkyl segment of the moiety, and typically
containing 1 to 5 aromatic rings. The term "aralkyl" will usually
be used to refer to aryl-substituted alkyl groups. The term
"aralkylene" will be used in a similar manner to refer to moieties
containing both alkylene and aryl species, typically containing
less than about 24 carbon atoms in the alkylene portion and 1 to 5
aromatic rings in the aryl portion, and typically aryl-substituted
alkylene. Exemplary aralkyl groups have the structure --(CH2)j-Ar
wherein j is an integer in the range of 1 to 24, more typically 1
to 6, and Ar is a monocyclic aryl moiety.
EXAMPLES
The practice of the present invention will employ, unless otherwise
indicated, conventional techniques of synthetic organic chemistry,
biochemistry, molecular biology, and the like, which are within the
skill of the art. Such techniques are explained fully in the
literature.
The following examples are put forth so as to provide those of
ordinary skill in the art with a complete disclosure and
description of how to perform the methods and use the compositions
disclosed and claimed herein. Efforts have been made to ensure
accuracy with respect to numbers (e.g., amounts, temperature, etc.)
but some errors and deviations should be accounted for. Unless
indicated otherwise, parts are parts by weight, temperature is in
.degree. C. and pressure is at or near atmospheric. Standard
temperature and pressure are defined as 20.degree. C. and 1
atmosphere.
The synthesis of polynucleotides has been well-studied, and methods
incorporate both aqueous and organic solvents. It is well known
that changing the solvent in a reaction system frequently affects
the performance of the reaction, sometimes profoundly. The ionic
nature of ionic liquids fundamentally differs from molecular nature
of aqueous or organic solvents used in various steps of the
polynucleotide synthesis cycle. Potential problems include changes
of chemical mechanism, possibly favoring different products due to
the ionic nature of the solvent. Stabilization of charged reaction
intermediates due to interaction with the ionic liquid, or chemical
reaction with components of the ionic liquid itself might be
expected. Will the short-lived reaction intermediates found in
conventional solvents be long-lived stable intermediates in an
ionic liquid? Will changes in the relative stabilities of reaction
intermediates change the available reaction pathways? Will the
expected changes in reaction kinetics shift the balance between
thermodynamic and kinetic control, and hence produce different
products?
We determined to study the effect of the coupling reaction in ionic
liquid solvent as an alternative to molecular solvents (aqueous and
organic solvents). We have discovered that, despite the previously
mentioned potential problems, we were able to achieve coupling of
nucleoside moieties via formation of an internucleotide bond in
ionic liquids. We have now found that various advantages exist in
performing the coupling reaction in ionic liquids. One advantage we
found was that the hydrophobicity of ionic liquid led to reduced
problems in dealing with hydrolysis of the reactants due to water
in the reaction environment. Less solvent may be used to wash in
between coupling steps, and ionic liquid solvents may be recovered
more easily, when compared to prior art methods. This may be
particularly useful in large-scale synthesis, where lots of washing
and solvents are required.
Particularly useful phosphoramidites, their preparation, and their
use are described in detail in U.S. Pat. No. 5,902,878; U.S. Pat.
No. 5,700,919; U.S. Pat. No. 4,668,777; U.S. Pat. No. 4,415,732;
PCT publication WO 98/41531 and the references cited therein, among
others.
The chemical synthesis of thymidine-thymidylate dimers in ionic
liquid were preformed by the following protocol:
3 molecular sieves were activated by drying in a vacuum oven at
200.degree. C. overnight. A small number of sieves were placed in a
5 ml, round bottom flask with a 14/20 ground glass joint that was
then sealed with a rubber septum. 3 ml of
1-ethyl-3-methyl-1H-imidazolium trifluoromethanesulfonate (Aldrich
Chemical Company, Milwaukee, Wis. USA) was added to the flask and
the liquid allowed to dry overnight.
5'-Dimethoxytrityl-2'-deoxyThymidine,
3'-[(2-cyanoethyl)-(N,N-diisopropyl)]-phosphoramidite, 0.38 grams,
0.5 mmol, was added to the flask and the solution shaken until the
reagent had dissolved. A small amount of the solution was removed
from the flask and placed in an NMR tube for analysis by .sup.31P
NMR using an external lock. The resulting NMR spectrum showed the
presence of the starting material nucleoside phosphoramidite at
.delta. 147.18 ppm relative to phosphoric acid.
3'-Acetyl Thymidine (ChemGenes Corp., Waltham Mass. USA) 0.14
grams, 0.5 mmol was added to the mixture along with tetrazole 0.18
grams, 2.5 mmol. The solution was shaken on a wrist action shaker
until the reagents were completely dissolved. An aliquot of the
reaction mixture was removed from the flask and placed in an NMR
tube for analysis by .sup.-P NMR using an external lock. The
resulting NMR spectrum (FIG. 2) showed complete conversion of the
starting material nucleoside phosphoramidite at .delta. 147.18 ppm
to the phosphite triester at .delta. 139.16 ppm.
In another example, 3' molecular sieves were activated by drying in
a vacuum oven at 200.degree. C. overnight. A small number of sieves
were placed in a 5 ml, round bottom flask with a 14/20 ground glass
joint that was then sealed with a rubber septum. 3 ml of
1-butyl-3-methyl-imidazolium tetrafluoroborate (Solvent Innovation
GmbH, 50679 Koln, Germany) was added to the flask and the liquid
allowed to dry overnight. 5'-Dimethoxytrityl-2'-deoxyThymidine,
3'-[(2-cyanoethyl)-(N,N-diisopropyl)]-phosphoramidite, 0.38 grams,
0.5 mmol, was added to the flask and the solution shaken until the
reagent had dissolved. A small amount of the solution was removed
from the flask and placed in an NMR tube for analysis by .sup.-P
NMR using an external lock. The resulting NMR spectrum (FIG. 3)
showed the presence of the starting material nucleoside
phosphoramidite at .delta. 146.94 ppm relative to phosphoric
acid.
3'-Acetyl Thymidine (ChemGenes Corp., Waltham Mass.) 0.14 grams,
0.5 mmol was added to the mixture along with tetrazole 0.18 grams,
2.5 mmol. The solution was shaken on a wrist action shaker until
the reagents were completely dissolved. An aliquot of the reaction
mixture was removed from the flask and placed in an NMR tube for
analysis by .sup.31P NMR using an external lock. The resulting NMR
spectrum (FIG. 4) showed complete conversion of the starting
material nucleoside phosphorarnidite at .delta. 146.94 ppm to the
phosphite triester diastereomers centered at .delta. 138.98
ppm.
The method of the above-described synthesis in the presence of
ionic liquids is applied to deposition of a nucleotide monomer,
oligonucleotide, or polynucleotide to a suitable substrate,
especially for the fabrication of polynucleotide arrays. An
apparatus as pictured in FIG. 4 may be used to contact the
insoluble planar substrate with the nucleotide monomer,
oligonucleotide, or polynucleotide dissolved in the solvent
comprising an ionic liquid. The apparatus shown in FIG. 4 includes
a substrate station 20 on which can be mounted a substrate 14.
Substrate station 20 can include a vacuum chuck connected to a
suitable vacuum source (not shown) to retain a substrate 14 without
exerting too much pressure thereon, since substrate 14 is often
made of glass. A dispensing head 210 is retained by a head retainer
208. Head 210 can be positioned to face substrate station 20 by a
positioning system. The positioning system includes a carriage 62
connected to substrate station 20, a transporter 60 controlled by a
processor 140 through line 66, and a second transporter 100
controlled by processor 140 through line 106. Transporter 60 and
carriage 62 are used execute one axis positioning of the station 20
facing the dispensing head 210 by moving station 20 in the
direction of arrow 63, while transporter 100 is used to provide two
axis adjustment of the position of head 210 in a vertical direction
202 or in the direction 204. Further, once substrate station 20 has
been positioned facing head 210, the positioning system will be
used to scan head 208 across a mounted substrate 14, typically line
by line (although other scanning configurations could be used).
However, it will be appreciated that both transporters 60 and 100,
or either one of them, with suitable construction, can be used to
perform any necessary positioning (including the foregoing
scanning) of head 210 with respect to any of the stations. Thus,
when the present application recites "positioning" one element
(such as head 210) in relation to another element (such as station
20) it will be understood that any required moving can be
accomplished by moving either element or a combination of both of
them.
The apparatus further includes a display 310, speaker 314, and
operator input device 312. Operator input device 312 may, for
example, be a keyboard, mouse, or the like. Processor 140 has
access to a memory 141, and controls head 210 (and activation of
the ejectors therein), operation of the positioning system,
operation of each jet in print head 210, display 310 and speaker
314. Memory 141 may be any suitable device in which processor 140
can store and retrieve data, such as magnetic, optical, or solid
state storage devices (including magnetic or optical disks or tape
or RAM, or any other suitable device). Any processor described
herein may include a general purpose digital microprocessor (such
as typically used in a programmable computer) suitably programmed
to execute all of the steps required by it, or any hardware or
software combination which will perform the required functions.
Head 210 may be of a type commonly used in an ink jet type of
printer and may, for example, have multiple drop dispensing
orifices communicating with one or more chambers for holding either
previously obtained polynucleotide solution (deposition method), or
a solution of a polynucleotide monomer (for in situ synthesis of
polynucleotides on the surface of the substrate 14). Ejectors are
positioned in the one or more chambers, each opposite a
corresponding orifice. For example, each ejector may be in the form
of an electrical resistor operating as a heating element under
control of processor 140 (although piezoelectric elements could be
used instead). Each orifice with its associated ejector and portion
of the chamber, defines a corresponding pulse jet. In this manner,
application of a single electric pulse to an ejector causes a
droplet to be dispensed from a corresponding orifice. Certain
elements of the head 210 can be adapted from parts of a
commercially available thermal inkjet print head device available
from Hewlett-Packard Co. as part no. HP51645A. One suitable head
configuration is described in more detail in U.S. patent
application entitled "A Multiple Reservoir Ink Jet Device for the
Fabrication of Biomolecular Arrays" by Caren et al., Ser. No.
09/150,507 filed Sep. 9, 1998, now U.S. Pat. No. 6,461,812.
Modifications to the above apparatus which may be made depending on
the array formation method are described in co-pending U.S. patent
applications entitled "Fabricating Biopolymer Arrays" by Webb et
al., Ser. No. 09/302,922 filed Apr. 30, 1999, now U.S. Pat. No.
6,323,043, and U.S. Patent No. 6,242,266 to Schleifer et al.
Following contact of the substrate with the ionic liquid solution
for a period of time and under conditions sufficient for the
nucleotide monomer, oligonucleotide, or polynucleotide to become
immobilized on the substrate surface, as described above, the
surface of the resultant array may be further processed as desired
in order to prepare the array for use. For example, further
iterations of the synthesis cycle may be performed for in situ
synthesis. As another example, the array surface may be washed to
removed unbound reagent, e.g. unreacted polymer, and the like. Any
convenient wash solution and protocol may be employed, e.g. flowing
an aqueous wash solution, e.g. water, methanol, acetonitrile, and
the like, across the surface of the array, etc. The surface may
also be dried and stored for subsequent use, etc.
The apparatus of FIG. 4 is useful for the practice of the
invention, but is not required, as a number of other known methods
are available and may be used for contacting the substrate with the
nucleotide monomer, oligonucleotide, or polynucleotide dissolved in
the solvent comprising an ionic liquid. Modifications of these
known methods within the capabilities of a skilled practitioner in
the art as well as other methods known to those of skill in the art
may be employed. For example, U.S. Pat. No. 6,110,426 to Shalon, et
al. describes a method of dispensing a known volume of a reagent at
each selected array position, by tapping a capillary dispenser on
the substrate under conditions effective to draw a defined volume
of liquid onto the substrate. Another method employs uses an array
of pins dipped into corresponding wells, e.g., the 96 wells of a
microtitre plate, for transferring an array of samples to a
substrate, such as a porous membrane. One such array of pins is
designed to spot a membrane in a staggered fashion, for creating an
array of 9216 spots in a 22 by 22 cm area (Lehrach, et al.,
"Hybrididization Fingerprinting in Genome Mapping and Sequencing,"
in Genome Analysis, Vol. 1 (1990, Davies and Tilgham, Eds., Cold
Spring Harbor Press), 39-81). A different method has been described
which uses a vacuum manifold to transfer a plurality, e.g., 96, of
aqueous samples of DNA from 3 millimeter diameter wells to a porous
membrane for making ordered arrays of DNA on a porous membrane,
i.e. a "dot blot" approach. A common variant of this procedure is a
"slot-blot" method in which the wells have highly-elongated oval
shapes. Khrapko, et al. (DNA Sequence 1:375-388 (1991)) describes a
method of making an oligonucleotide matrix by spotting DNA onto a
thin layer of polyacrylamide. The spotting is done manually with a
micropipette. Another alternate method of creating ordered arrays
of nucleic acid sequences involving synthesizing different nucleic
acid sequences at different discrete regions of a substrate has
been described. See Fodor et al., Science 251:767-773 (1991). A
related method has been described by Southern, et al. Genomics
13:1008-1017 (1992). See also U.S. Pat. No. 5,143,854 to Pirrung et
al., and PCT patent publications WO 90/15070 and 92/10092 for
further methods for making arrays of oligonucleotide probes by
depositing solutions of reagents on a substrate surface.
Still other methods and apparatus for fabrication of polynucleotide
arrays are described in, e.g. U.S. Pat. No. 6,242,266 to Schleiffer
et al., which describes a fluid dispensing head for dispensing
droplets onto a substrate, and methods of positioning the head in
relation to the substrate. U.S. Pat. No. 6,180,351 to Cattell and
U.S. Pat. No. 6,171,797 to Perbost describe additional methods
useful for fabricating polynucleotide arrays. Methods for
fabrication of arrays may include, for example, using a pulse jet
such as an inkjet type head to deposit a droplet of reagent
solution for each feature. Such a technique has been described, for
example, in PCT publications WO 95/25116 and WO 98/41531, and
elsewhere. In such methods, the head has at least one jet which can
dispense droplets of a fluid onto a substrate, the jet including a
chamber with an orifice, and including an ejector which, when
activated, causes a droplet to be ejected from the orifice. The
head may particularly be of a type commonly used in inkjet
printers, in which a plurality of pulse jets (such as those with
thermal or piezoelectric ejectors) are used, with their orifices on
a common front surface of the head. The head is positioned with the
orifice facing the substrate. Multiple fluid droplets (where the
fluid comprises the nucleotide monomer, oligonucleotide, or
polynucleotide dissolved in the solvent comprising an ionic liquid)
are dispensed from the head orifice so as to form an array of
droplets on the substrate (this formed array may or may not be the
same as the final desired array since, for example, multiple heads
can be used to form the final array and multiple passes of the
head(s) may be required to complete the array).
As is well known in the ink jet print art, the amount of fluid that
is expelled in a single activation event of a pulse jet, can be
controlled by changing one or more of a number of parameters,
including the orifice diameter, the orifice length (thickness of
the orifice member at the orifice), the size of the deposition
chamber, and the size of the heating element, among others. The
amount of fluid that is expelled during a single activation event
is generally in the range about 0.1 to 1000 pL, usually about 0.5
to 500 pL and more usually about 1.0 to 250 pL. A typical velocity
at which the fluid is expelled from the chamber is more than about
1 m/s, usually more than about 10 m/s, and may be as great as about
20 m/s or greater. As will be appreciated, if the orifice is in
motion with respect to the receiving surface at the time an ejector
is activated, the actual site of deposition of the material will
not be the location that is at the moment of activation in a
line-of-sight relation to the orifice, but will be a location that
is predictable for the given distances and velocities.
It should be specifically understood though, that the present
invention is not limited to pulse jet type deposition systems. In
particular, any type of array fabricating apparatus can be used to
contact the substrate with the ionic liquid solution, including
those such as described in U.S. Pat. No. 5,807,522, or apparatus
which may employ photolithographic techniques for forming arrays of
moieties, such as described in U.S. Pat. No. 5,143,854 and U.S.
Pat. No. 5,405,783, or any other suitable apparatus which can be
used for fabricating arrays of moieties. For example, robotic
devices for precisely depositing aqueous volumes onto discrete
locations of a support surface, i.e. arrayers, are also
commercially available from a number of vendors, including: Genetic
Microsystems; Cartesian Technologies; Beecher Instruments; Genomic
Solutions; and BioRobotics. Other methods and apparatus are
described in U.S. Pat. Nos. 4,877,745; 5,338,688; 5,474,796;
5,449,754; 5,658,802; and 5,700,637. Patents and patent
applications describing arrays of biopolymeric compounds and
methods for their fabrication include: U.S. Pat. Nos. 5,242,974;
5,384,261; 5,405,783; 5,412,087; 5,424,186; 5,429,807; 5,436,327;
5,445,934; 5,472,672; 5,527,681; 5,529,756; 5,545,531; 5,554,501;
5,556,752; 5,561,071; 5,599,695; 5,624,711; 5,639,603; 5,658,734;
WO 93/17126; WO 95/11995; WO 95/35505, WO 97/14706, WO 98/30575; EP
742 287; and EP 799 897. See also Beier et al. "Versatile
derivatisation of solid support media for covalent bonding on
DNA-microchips", Nucleic Acids Research (1999) 27: 1970-1977.
In general, the product of the coupling reaction when performed in
the 5' to 3' direction, when performed in a solid phase system upon
an insoluble planar substrate, may be represented by the following
structural formula:
##STR00003## Wherein:
.smallcircle. represents the insoluble planar substrate or an
oligonucleotide chain bound to the insoluble planar substrate;
A represents H or an optionally protected hydroxyl group;
B is a purine or pyrimidine base whose exocyclic amine functional
group is optionally protected; and
R is a suitable protecting group,
"Y" is hydrido or hydrocarbyl, typically alkyl, alkenyl, aryl,
aralkyl, or cycloalkyl. Preferably, Y represents: lower alkyl;
electron-withdrawing .beta.-substituted aliphatic, particularly
electron-withdrawing .beta.-substituted ethyl such as
.beta.-trihalomethyl ethyl, .beta.-cyanoethyl, .beta.-sulfoethyl,
.beta.-nitro-substituted ethyl, and the like; electron-withdrawing
substituted phenyl, particularly halo-, sulfo-, cyano- or
nitro-substituted phenyl; or electron-withdrawing substituted
phenylethyl. Most preferably, Y represents methyl,
.beta.-cyanoethyl, or 4-nitrophenylethyl.
The synthetic methods of the invention may be conducted on any
substrate having a surface to which chemical entities may bind.
Preferred substrate materials provide physical support for the
deposited material and endure the conditions of the deposition
process and of any subsequent treatment or handling or processing
that may be encountered in the use of the particular array.
Suitable substrates may have a variety of forms and compositions
and may derive from naturally occurring materials, naturally
occurring materials that have been synthetically modified, or
synthetic materials. Examples of suitable support materials
include, but are not limited to, nitrocellulose, glasses, silicas,
teflons, and metals (for example, gold, platinum, and the like).
Suitable materials also include polymeric materials, including
plastics (for example, polytetrafluoroethylene, polypropylene,
polystyrene, polycarbonate, and blends thereof, and the like),
polysaccharides such as agarose (e.g., that available commercially
as Sepharose.RTM., from Pharmacia) and dextran (e.g., those
available commercially under the tradenames Sephadex.RTM. and
Sephacyl.RTM., also from Pharmacia), polyacrylamides, polystyrenes,
polyvinyl alcohols, copolymers of hydroxyethyl methacrylate and
methyl methacrylate, and the like.
Prior to being contacted with the solution containing the ionic
liquid and the nucleotide monomer, oligonucleotide, or
polynucleotide, the insoluble substrate has a surface reactive
group which, when contacted with the solution, reacts to covalently
bind the nucleotide monomer, oligonucleotide, or polynucleotide to
the substrate. The surface reactive group may vary in different
embodiments of the invention. In one embodiment, the surface
reactive group is part of the composition of the planar substrate
base material. In another embodiment, modifications to the surface
of the base material may present a different surface reactive group
than possible from the base material itself. Such modifications may
include one or more different layers of compounds that serve to
modify the properties of the surface in a desirable manner. Such
modification layers include, but are not limited to, inorganic and
organic layers such as metals, metal oxides, polymers, small
organic molecules and the like. Polymeric layers of interest
include layers of: peptides, proteins, polynucleic acids or
mimetics thereof (for example, peptide nucleic acids and the like);
polysaccharides, phospholipids, polyurethanes, polyesters,
polycarbonates, polyureas, polyamides, polyethyleneamines,
polyarylene sulfides, polysiloxanes, polyimides, polyacetates, and
the like, where the polymers may be hetero- or homopolymeric.
Modifications of insoluble substrate materials may or may not have
separate functional moieties attached thereto.
The substrate may be functionalized to form a "linking moiety"
having a surface reactive group to bond to the first deposited
monomer. Suitable techniques for functionalizing substrates with
such linking moieties are described, for example, in Southern, E.
M., Maskos, U. and Elder, J. K., Genomics, 13: 1007-1017, 1992. The
initial monomer of the oligonucleotide to be synthesized on the
substrate surface is typically bound to a linking moiety which is
in turn bound to a surface hydrophilic group, e.g., to a surface
hydroxyl moiety present on a silica substrate. Methods similar to
those disclosed in, e.g. U.S. Pat. No. 5,688,642 to Chrisey et al.,
may be used. The Chrisey et al. '642 patent describes coating a
substrate with molecules, such as aminosilanes, whose reactivity
with nucleic acid molecules can be transformed by irradiation; this
patent also teaches the use of a heterobifunctional crosslinker to
promote covalent binding of the nucleic acid oligomers to the
coating molecules. In yet another embodiment of the current
invention, the surface reactive group may be located upon a
nucleoside moiety immobilized upon the substrate base material
(e.g. via a direct bond to the base material or via a surface
modification of the base material). The nucleoside moiety may be a
portion of an immobilized nucleotide monomer, a portion of an
immobilized oligonucleotide, or a portion of an immobilized
polynucleotide. The surface reactive group may include a hydroxyl
group, e.g. a 3' or 5' hydroxyl group of a terminal nucleoside
moiety of an immobilized nucleoside, immobilized oligonucleotide,
or immobilized polynucleotide.
In array fabrication, the quantities of polynucleotide available
are usually very small and expensive. Additionally, sample
quantities available for testing are usually also very small and it
is therefore desirable to simultaneously test the same sample
against a large number of different probes on an array. Therefore,
one embodiment of the invention provides for fabrication of arrays
with large numbers of very small, closely spaced features Arrays
may be fabricated with features that may have widths (that is,
diameter, for a round spot) in the range from a minimum of about 10
micrometers to a maximum of about 1.0 cm. In embodiments where very
small spot sizes or feature sizes are desired, material can be
deposited according to the invention in small spots whose width is
in the range about 1.0 micrometer to 1.0 mm, usually about 5.0
micrometers to 0.5 mm, and more usually about 10 micrometers to 200
micrometers. Interfeature areas will typically (but not
essentially) be present which do not carry any polynucleotide. It
will be appreciated though, that the interfeature areas could be of
various sizes and configurations.
Referring now to FIGS. 2 and 3, the invention as described herein
may be practiced to produce one or more arrays 12 (only some of
which are shown in FIG. 2) across the surface of a single substrate
14. The arrays 12 produced on a given substrate need not be
identical and some or all could be different. FIG. 3 depicts a
single array 12 having multiple spots or features, 16. An array 12
may contain any number of features, generally including at least
tens of features, usually at least hundreds, more usually
thousands, and as many as a hundred thousand or more features. All
of the features 16 may be different, or some or all could be the
same. Each feature 16 carries a predetermined moiety or a
predetermined mixture of moieties, such as a particular
polynucleotide sequence or a predetermined mixture of
polynucleotides. The features of the array may be arranged in any
desired pattern, e.g. organized rows and columns of features (for
example, a grid of features across the substrate surface), a series
of curvilinear rows across the substrate surface (for example, a
series of concentric circles or semi-circles of features), and the
like. In embodiments where very small feature sizes are desired,
the density of features on the substrate may range from at least
about ten features per square centimeter, or preferably at least
about 35 features per square centimeter, or more preferably at
least about 100 features per square centimeter, and up to about
1000 features per square centimeter, or preferably up to about
10,000 features per square centimeter, or more preferably up to
100,000 features per square centimeter. Each feature carries a
predetermined polynucleotide (which includes the possibility of
mixtures of polynucleotides).
In one embodiment, about 10 to 100 of such arrays can be fabricated
on a single substrate (such as glass). In such embodiment, after
the substrate has the polynucleotides on its surface, the substrate
may be cut into substrate segments, each of which may carry one or
two arrays. It will also be appreciated that there need not be any
space separating arrays from one another. Where a pattern of arrays
is desired, any of a variety of geometries may be constructed,
including for example, organized rows and columns of arrays (for
example, a grid of arrays, across the substrate surface), a series
of curvilinear rows across the substrate surface (for example, a
series of concentric circles or semi-circles of arrays), and the
like.
The array substrate may take any of a variety of configurations
ranging from simple to complex. Thus, the substrate could have
generally planar form, as for example a slide or plate
configuration, such as a rectangular or square or disc. In many
embodiments, the substrate will be shaped generally as a
rectangular solid, having a length in the range about 4 mm to 300
mm, usually about 4 mm to 150 mm, more usually about 4 mm to 125
mm; a width in the range about 4 mm to 300 mm, usually about 4 mm
to 120 mm and more usually about 4 mm to 80 mm; and a thickness in
the range about 0.01 mm to 5.0 mm, usually from about 0.1 mm to 2
mm and more usually from about 0.2 to 1 mm. The substrate surface
onto which the polynucleotides are bound may be smooth or
substantially planar, or have irregularities, such as depressions
or elevations. The configuration of the array may be selected
according to manufacturing, handling, and use considerations.
Ionic liquids that may be used include organic salts that are fluid
below about 80.degree. C. at around normal atmospheric pressure
(about 1 atmosphere at sea level). The organic salts generally have
an organic cation and either an inorganic or organic counterion.
The organic cation is preferably an N-substituted pyridine having
the following structure:
##STR00004##
wherein R is alkyl and each R' is independently selected from
hyrido, alkyl, or halogen;
or a 1,3 di-substituted imidazole having the following
structure:
##STR00005##
wherein each R is independently selected from alkyl, each R' is
independently selected from hydrido, alkyl, or halogen, and R'' is
selected from hydrido or methyl.
Preferred organic cations include 1,3-dimethyl-imidazolium,
1-ethyl-3-methyl-imidazolium, 1-butyl-3-methyl-imidazolium,
1-hexyl-3-methyl-imidazolium, 1-decyl-3-methyl-imidazolium,
1-dodecyl-3-methyl-imidazolium, 1-methyl-3-octyl-imidazolium,
1-methyl-3-tetradecyl-imidazolium,
1,2-dimethyl-3-propyl-imidazolium,
1-ethyl-2,3-dimethyl-imidazolium, 1-butyl-2,3-dimethyl-imidazolium,
N-ethylpyridinium, N-butylpyridinium, N-hexylpyridinium,
4-methyl-N-butyl-pyridinium, 3-methyl-N-butyl-pyridinium,
4-methyl-N-hexyl-pyridinium, 3-methyl-N-hexyl-pyridinium,
4-methyl-N-octyl-pyridinium, 3-methyl-N-octyl-pyridinium,
3,4-dimethyl-N-butyl-pyridinium, and
3,5-dimethyl-N-butyl-pyridinium.
Preferred anions of the ionic liquid are chloride (Cl.sup.-),
bromide (Br.sup.-), tetrafluoroborate ([BF.sub.4].sup.-),
hexafluorophosphate ([PF.sub.6].sup.-), [SbF.sub.6].sup.-,
[CuCl.sub.2].sup.-, [AlCl.sub.4].sup.-, [Al.sub.2Cl.sub.7].sup.-,
[Al.sub.3Cl.sub.10].sup.-, methylsulfate (CH.sub.3SO.sub.4.sup.-),
trifluoroacetate (CF.sub.3CO.sub.2.sup.-), heptafluorobutanoate
(CF.sub.3(CF.sub.2).sub.2CO.sub.2.sup.-), triflate
(CF.sub.3SO.sub.2.sup.-), nonaflate (C.sub.2F.sub.5SO.sub.2.sup.-),
bis(trifluoromethylsulfonyl)imide
((CF.sub.3SO.sub.2).sub.2N.sup.-),
bis(perfluoroethylsulfonyl)imide((C.sub.2F.sub.5SO.sub.2).sub.2N.sup.-),
and
tris(trifluoromethylsulfonyl)methide((CF.sub.3SO.sub.2).sub.3C.sup.-)-
. Ionic liquids are available from Covalent Associates (Woburn,
Mass.), Aldrich Chemical Company Milwaukee, Wis.), Solvent
Innovation (Koln, Germany), and Acros Organics (Geel, Belgium).
In one embodiment, to perform the coupling reaction, a nucleotide
monomer, oligonucleotide, or polynucleotide is dissolved in a
solution having at least 98 percent by weight of ionic liquid,
whereupon an insoluble substrate, preferably a planar substrate, is
contacted with the solution containing ionic liquid and the
nucleotide monomer, oligonucleotide, or polynucleotide. In other
embodiments, the solution has at least about 90% ionic liquid, or
at least about 75% ionic liquid, or at least about 50% ionic
liquid, or at least about 25% ionic liquid, or at least about 10%
ionic liquid. Co-solvents that may be mixed into the ionic liquid
include but are not limited to acetonitrile, tetrahydrofuran,
dimethylformamide, methylene chloride, propylene carbonate,
adiponitrile, toluene, dioxane, dimethylsulfoxide, and N-methyl
pyrrolidone. In another embodiment, the nucleotide monomer,
oligonucleotide, or polynucleotide is dissolved in a solvent that
is 100 percent by weight ionic liquid. An activator compound is
typically included in a concentration of about 0.05 molar up to
about 0.5 molar. The activator is generally tetrazole,
S-ethyl-thiotetrazole, 4-nitrotriazole, or dicyanoimidazole,
although other acidic azoles may be used. One potential advantage
of using an ionic liquid is that the ionic liquid may serve as the
activator.
In one embodiment of the invention, a monomer nucleoside
phosphoramidite is dissolved in the solvent comprising the ionic
liquid, and the resulting solution is deposited upon the surface of
the planar substrate, and the process is repeated multiple times,
analogous to conventional polynucleotide synthesis. The invention
also encompasses the formation of an internucleotide bond between
two polynucleotides or oligonucleotides, or between a
polynucleotide and an oligonucleotide, resulting in an extended
polynucleotide immobilized on the array surface. In such case, one
of the polynucleotides or oligonucleotides is dissolved in the
solvent comprising the ionic liquid, and the substrate to be
contacted with the solution bears the other polynucieotide or
oligonucleotide. The skilled practitioner in the art will realize
that one of the nucleoside moieties must be activated, as in a
phosphoramidite. Such modification is well known in the art. The
invention also encompasses embodiments where the oligonucleotide or
polynucleotide dissolved in the solvent comprise modified
oligonucleotides or modified polynucleotides, especially where the
modified oligo- or -polynucleotides are "activated", or more
susceptible to bond formation. Such modification of the oligo- or
poly-nucleotides may be accomplished using known chemistries
previously used for immobilizing oligo- or polynucleotides to
insoluble substrates. Examples of such modifications may be found
in: Polymer-supported Reactions in Organic Chemistry, Hodge, P.
& Sherrington, D. C., (John Wiley & Sons, New York, N.Y.
1980); Advanced Organic Chemistry of Nucleic Acids, Shabarova, Z.
& Bogdanov, A., (VCH, Weinheim, Germany 1994), pages
531-545.
In the case of array fabrication, different nucleotide monomers and
activator may be deposited at different addresses on the substrate
during any one cycle so that the different features of the
completed array will have polynucleotides with different sequences.
One or more intermediate further steps may be required in each
cycle, such as the conventional oxidation, capping and washing
steps in the case of in situ fabrication of polynucleotide arrays
(these steps may be performed by flooding the array surface with
the appropriate reagents).
In certain embodiments of the invention, the probes are arranged on
the substrate either by immobilization, e.g. by covalent
attachment, of a pre-synthesized probe, or by synthesis of the
probe on the substrate (in situ synthesis). In fabricating a
polynucleotide array, typically each region on the substrate
surface on which an array will be or has been formed ("array
regions") is completely exposed to one or more reagents. For
example, the array regions will often be exposed to one or more
reagents to form a suitable layer on the surface which binds to
both the substrate and the polynucleotide. In in situ synthesis the
array regions will also typically be exposed to the oxidizing,
deblocking, and optional capping reagents. Similarly, particularly
in fabrication by depositing previously obtained oligonucleotides
or polynucleotides, it may be desirable to expose the array regions
to a suitable blocking reagent to block locations on the surface at
which there are no features from non-specifically binding to
target.
In the conventional synthesis method depicted schematically in FIG.
1, it is typical to use an aqueous solution of iodine for the
oxidation step. However, phosphoramidite reagents that have been
activated for coupling are highly reactive with water. The
invention may be extended to include using ionic liquids as
solvents elsewhere in the synthesis cycle to reduce or
substantially eliminate the presence of water during oxidation and
deprotection. Thus, for example, in polynucleotide array synthesis,
the current invention may allow the number of wash steps (with
non-aqueous solvent) over all of the addresses on the surface of
the array to be reduced, with potential concomitant savings in time
and solvents.
The method of the invention lends itself to synthesis of
polynucleotides on array substrates in either the 3'-to-5' or the
5'-to-3' direction. In the latter case, the initial step of the
synthetic process involves attachment of an initial nucleoside to
the array substrate at the 5' position, leaving the 3' position
available for covalent binding of a subsequent monomer. The
coupling reaction in which the nucleoside monomer becomes
covalently attached to the 3' hydroxyl moiety of the substrate
bound nucleoside is conducted under reaction conditions essentially
identical to those described for the 3'-to-5' synthesis. The
synthesis cycle is then continued with the (optional) capping step,
the oxidation of the internucleotide bond, and the deprotection of
the active site hydroxyl in preparation for the next synthesis
cycle, which is repeated until a polynucleotide having the desired
sequence and length is obtained. The synthesis is repeated at each
address of the array to build up the desired sequence
polynucleotide at each address of the array. Following synthesis,
the polynucleotide may, if desired, be cleaved from the solid
support. The details of the synthesis in either the 3'-to-5' or the
5'-to-3' direction will be readily apparent to the skilled
practitioner based on the prior art and the disclosure contained
herein.
In particular embodiments, the reaction is geared to producing
planar substrates having immobilized thereupon "native"
polynucleotides, i.e. substantially identical to those that might
be isolated from nature. In other embodiments, polynucleotide
analogues may be immobilized upon the planar substrate, where the
polynucleotide analogues may have `modified` (not occurring in
nature) phosphodiester backbones or modified bases attached to the
sugar groups in the phosphodiester backbones. In another
embodiment, after the dissolved nucleotide monomer,
oligonucleotide, or polynucleotide has been immobilized to the
planar substrate, it is modified, e.g. by oxidation, to form the
ultimate polynucleotide product. The present invention encompasses
materials and methods for use in fabricating insoluble substrates
having immobilized thereupon polynucleotides, polynucleotide
intermediates, and/or polynucleotide analogues. The invention also
encompasses reagents and methods allowing the immobilization of the
polynucleotides/intermediates/analogues to be conducted under a
wide range of conditions and allowing for the use of a variety of
protecting groups. This wide range includes the use of solvents
comprising one or more ionic liquids and, optionally, one or more
co-solvents.
While the foregoing embodiments of the invention have been set
forth in considerable detail for the purpose of making a complete
disclosure of the invention, it will be apparent to those of skill
in the art that numerous changes may be made in such details
without departing from the spirit and the principles of the
invention. Accordingly, the invention should be limited only by the
following claims.
All patents, patent applications, and publications mentioned herein
are hereby incorporated by reference in their entireties.
* * * * *