Protected linker compounds

Abstract

The invention features protected linker compounds which comprise at one terminus a protected amino group and at another other terminus a phosphorous activating group, such as a phosphoramidite group. These protected linker compounds are introduced chemically at the 5-end of oligonucleotides for the purpose of preparing 5-amino modified oligonucleotides. After deprotection, the thereby introduced amino group then allows further modification (e.g. attachment of dyes) or immobilization (on surfaces or beads) of the oligonucleotide. Specifically, the presented amino protecting group is designed to provide such protected linker compounds in a solid form, which facilitates efficient purification by precipitation or crystallization and aliquoting for distribution and storage.

Claims

1. An amino linker building block suitable for preparing 5 amino-modified oligonucleotides comprising a linker covalently bonded between a phosphoramidite moiety and an amino protecting group, wherein the amino protecting group comprises a 1,4-diamide substructure, with two amide groups comprising a C1 and a C4 carbon atom of the 1,4-diamide substructure, wherein the 1,4 diamide substructure is part of an aromatic system in which two neighboring carbon atoms of the aromatic system constitute a 2- and 3- position of the 1,4-diamide substructure, and wherein a nitrogen of one of the amide groups is covalently bonded to the linker and the nitrogen of the other of the two amide groups is not bonded to the linker.

2. An amino linker building block according to claim 1 wherein both of the amide groups are N-mono-substituted amides comprising a hydrogen atom at each amide nitrogen.

3. The amino linker building block of claim 2, wherein the amino linker is a solid.

4. An amino linker building block having the structure of Formula III: ##STR00024## wherein R1 and R2 are independently hydrogen or a substituted C-atom; wherein R3 and R4 are independently hydrogen, halogen, nitro, C.sub.1-4 alkyl, C.sub.1-4 alkoxy or C.sub.1-4 alkoxyalkyl; wherein the linker is a linear or branched hydrocarbon chain which is optionally substituted or interrupted by one or more functional groups and/or hetero atoms and wherein the linker comprises up to 50 C atoms; wherein PN is the phosphoramidite moiety bonded to the linker and having the structure: ##STR00025## wherein Rx is a methyl or cyanoethyl group and wherein Ry and Rz are independent alkyl-groups comprising one to six C-atoms; and wherein Y is a substructure leading to an aromatic system selected from one of the substructures according to Formulas Y.1 to Y.6 ##STR00026## wherein R5 and R6 are independently hydrogen, halogen, nitro, C.sub.1-4 alkyl, C.sub.1-4 alkoxy or C.sub.1-4 alkoxyalkyl; ##STR00027## ##STR00028## ##STR00029## ##STR00030## wherein R7 to R10 are independently hydrogen, halogen, nitro, C.sub.1-4 alkyl, C.sub.1-4 alkoxy or C.sub.1-4 alkoxyalkyl; ##STR00031## wherein R11 is hydrogen, C.sub.1-4 alkyl, aryl or C.sub.1-4 alkoxyalkyl.

5. The amino linker building block according to claim 4, wherein the linker comprises alkyl-, cycloalkyl-, alkyl- aryl-, alkylene-, alkenylene-, aryl-alkylene-, alkynylene-, aryl-alkynylene-, alkoxy-, ether, amide or oligoethyleneglycol linear or branched linker chain segments and/or substituents and wherein said linker optionally comprises heteroatoms and wherein said linker comprises a total of less than 50 C-atoms.

6. The amino linker building block according to claim 4, wherein the linker is an aliphatic chain selected from the group consisting of an alkyl chain and a heteroalkyl chain.

7. The amino linker building block according to claim 6, wherein R2 to R6 are hydrogen (Formula III-Y.1) and R1 is hydrogen or a substituted C-atom.

8. The amino linker building block according to claim 4, wherein R2 to R6 are hydrogen, R1 is methyl, and wherein Rx is cyanoethyl and Ry and Rz are isopropyl.

9. The amino linker building block of claim 1 wherein the amino linker building block is a solid.

10. The amino linker building block according to claim 9, wherein the 1,4-diamide substructure is part of an aromatic system, in which two neighbouring C-atoms of the aromatic system constitute a 2-and a 3-position of the 1,4-diamide substructure.

11. The amino linker of claim 4, having the structure according to Formula XIV: ##STR00032##

12. The amino linker of claim 4, having the structure according to Formula XV: ##STR00033##

13. The amino linker of claim 4, having the structure according to Formula XVI: ##STR00034##

14. The amino linker building block of claim 4, wherein R.sub.1 and R.sub.2 are independently C.sub.1-12 alkyl, or C.sub.1-12 alkoxyalkyl, or C.sub.1-12 alkyl aryl.

15. The amino linker building block of claim 14, wherein R.sub.1 and R.sub.2 are independently C.sub.1-6 alkyl or C.sub.1-6 alkoxyalkyl.

16. The amino linker building block of claim 14, wherein R.sub.1 and R.sub.2 are independently methyl ethyl, propyl, butyl or pentyl.

17. The amino linker building block of claim 5, wherein the linker comprises less than 25 C-atoms.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 defines the term 1,4-diamide with numbering of the involved C-atoms and shows its connection to aromatic systems relevant to the here presented amino protecting groups and amino linker compounds

(2) FIG. 2 presents an overview over some exemplary alternative pathways for the method of synthesis of an exemplary embodiment of the amino linker building block according to Formula III.

(3) FIG. 3 depicts exemplary embodiments of the methods of production of the amino linker building block according to Formula IX. Methods A 1, A2 and A3 are alternatives for the formation of the phthalimide X under various conditions, Step B is the phosphitylation with 2-cyanoethyl diisopropylphosphoramidochloridite and N-ethyl-N,N-diisopropylamine in dichloromethane, and Step C is the ring-opening with methylamine in methanol, followed by precipitation of product according to Formula IX in dichloromethane/hexanes.

(4) FIG. 4 presents an overview of an exemplary coupling of a exemplary protected amino linker phosphoramidite building block according to Formula IX to a protected and immobilized nucleic acid molecule in Step 1 followed by deprotection of the 5 amino group, in Step 2, resulting in the formation of a 5-amino linker modified DNA oligonucleotide according to Formula XIII.

(5) FIG. 5 shows the deprotection mechanism of an exemplary protected amino linker group covalently bound to a DNA molecule under exemplary conditions with methylamine (L=linker).

(6) FIG. 6 Pictures of exemplary solid amino linker phosphoramidites according to the general Formula IX, in particular according to Formula XIV, Formula XV and Formula XVI in FIGS. 6A, 6B and 6C, respectively.

(7) FIG. 7 Stability of an exemplary amino linker according to the prior art (Formula I) and according to an embodiment of the invention (Formula XIV) under storage conditions, as measured after the indicated duration of storage at room temperature by 31P-NMR analysis.

(8) FIG. 8 gives an overview over the results of the deprotection reaction of a model diamide compound under the indicated conditions by 1H-NMR spectroscopy (300 MHz) in D2O.

(9) FIG. 9 shows HPLC traces (left) and ESI MS spectra (right) of a crude 5-aminolinker DNA sequence (Formula XVII) (top) and its crude digoxigenine conjugate (Formula XVIII) (bottom).

DETAILED DESCRIPTION OF THE INVENTION

(10) Reference will now be made in detail to a presently preferred embodiments of the invention, examples of which are fully represented in the accompanying formulas. Such examples are provided by way of explanation of the invention, not as a limitation thereof. In fact, it will be apparent to those skilled in the art various modifications and variations can be made in the present invention without departing from the spirit and scope thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield still a further embodiment. Still further, variations and selections of chemicals or materials and/or characteristics may be practiced to satisfy particular desired user criteria. Thus it is intended that the present invention cover such modifications and variations as come within the scope of the present features and their equivalents.

(11) In one exemplary embodiment according to the first aspect of the invention the amino linker compounds has the chemical structure according to Formula IX:

(12) ##STR00018##

(13) In the amino linker building block according to Formula IX, the amino group is protected by a phthalic diamide group. The amino group is thereby covalently bound via a stable amide bond to the protecting group. Such amino linker building blocks are not soluble in apolar solvents or mixtures of solvents and can therefore easily be precipitated by treating a solution of the compounds in e.g. dichloromethane with an apolar solvent such as hexanes.

(14) In the second aspect of the invention, methods of producing the protected amino linker phosphoramidite building blocks are provided.

(15) In FIG. 2 an overview over some exemplary alternative pathways for methods of production of an exemplary embodiment of the amino linker building block according to Formula III is presented. The preparation or provision of an appropriate cyclic precursor molecule is called Step A (some examples are given in FIG. 3). The addition step of a phosphorous activation group, e.g. a phosphoramidite, is called Step B. The ring opening step is called Step C in FIG. 2 (and also in FIG. 3 described further below). As exemplary methods, in two alternative pathways shown in FIG. 2 the sequence of the Steps B and C, i.e. of addition of the phosphoramidite group and of the ring-opening step, is interchanged. As further exemplary method, a third alternative pathway is shown in FIG. 2: a substituted or non-substituted cyclic imide precursor is provided by Step A and is opened during the reaction with an amino substituted linker alcohol to form a protected amino linker diamide intermediate in Step C to which in a Step B a phosphoramidite group is added. Furthermore, in a Step D of embodiments of methods of preparing amino linker building blocks, amino linker phosphoramidite building blocks are precipitated or crystallized.

(16) In FIG. 3 exemplary embodiments of the methods of production of 5 protected amino linker phosphoramidite building blocks according to Formula IX are further detailed. In particular, examples of Step A with exemplary formation of a hydroxyl linker-phthalimide compound, N-(hydroxyalkyl)phthalimide (according to Formula X) is outlined according to e.g method A1 or method A2 or method A3 under various, well-known conditions is formed as described below:

(17) A1) From the cyclic anhydride of a suitable substituted benzene 1,2-dicarboxylic acid (e.g. unsubstituted or substituted phthalic anhydride) which is treated with an amino alcohol (H.sub.2N-Linker-OH) in a high-boiling solvent capable of removing water azeotropically, typically toluene. At the reflux temperature of toluene, the corresponding cyclic phthalimide is formed and the bye-product water is removed azeotropically. A2) From the cyclic imide of a suitable substituted benzene 1,2-dicarboxylic acid (e.g. unsubstituted or substituted phthalimide) which is treated with a diol (HO-Linker-OH) under Mitsunobu conditions (dialkyl azodicarboxylate and triphenylphosphine in THF). A3) From the cyclic imide of a suitable substituted benzene 1,2-dicaboxylic acid (e.g. unsubstituted or substituted phthalimide) which is deprotonated with a strong base (e.g. KOH or NaH) and alkylated with a halogenated alcohol (X-Linker-OH).

(18) FIG. 3 further shows an exemplary phosphitylation step B, in which Alcohol X, N-(hydroxyalkyl)phthalimide, is then transformed into the corresponding phosphoramidite XI by treatment with an phosphoramidochloridite in the presence of a base or with an phosphordiamidite in the presence of an acid. In a further exemplary ring opening Step C the imide XI is treated with an amine to obtain the amino linker building block IX.

(19) In FIGS. 2 and 3, reference has been made to presently preferred embodiments of the invention, examples of which are fully represented in the accompanying formulas. However, such examples are provided by way of explanation of the invention and not limitation thereof. Analogous methods to those presented in FIGS. 2 and 3 for the production of the exemplary protected linker compound according Formula IX are readily available for the production of other embodiments of amino linker compounds according to Formula III by appropriate selection of the substituents, of the cyclic precursor and of the specific linker and of the specific phosphoramidite moiety according to a specifically desired embodiment of a Formula III protected linker compound. For example, analogous methods of production for synthesizing amino linker building blocks are also applicable to cyclic imides other than to substituted or non-substituted phthalimides. Variations and combinations of different embodiments are within the scope of the invention.

(20) The third aspect of the invention relates to the method of coupling protected linker compounds and more specifically to the coupling of protected amino linker phosphoramidite building blocks to a nucleic acid molecule or derivative thereof and furthermore to the deprotection of the protected amino group removing the amino protecting group off the nucleic acid molecule or derivative thereof.

(21) In an exemplary method of preparing a 5-amino modified nucleic acid, a building block of the exemplary Formula IX is coupled to a previously assembled, immobilized and protected oligonucleotide containing a free 5-OH group at the 5-end, followed by oxidation to the corresponding phosphoric acid triester and deprotecting with methylamine or ammonia/methylamine mixtures in solution or in the gas phase.

(22) In FIG. 4 an exemplary method of preparing a 5 amino modified nucleic acid according to Formula XIII by coupling an exemplary protected amino linker phosphoramidite building block of formula IX to a previously assembled, immobilized and protected nucleic acid molecule containing a free 5-OH group at the 5 end in Step 1. In subsequent Step 2 deprotection of the protected amino group of this intermediate XII is shown according to the following disclosed methodologies:

(23) In Step 1, the protected amino linker phosphoramidite building block is coupled on a nucleic acid synthesizer comprising the individual steps (i), (ii) and (iii) wherein the sequence of steps (ii) and (iii) is interchangeable:

(24) (i) Coupling reaction to an immobilized, protected oligonucleotide containing a free 5-OH group. This reaction is typically carried out in an aprotic polar solvent, such as acetonitrile, and in the presence of a weak HN acid, such as a (substituted) tetrazole or imidazole.

(25) (ii) Capping of the unreacted 5-OH group and cleavage of undesired coupling products at nucleobase moieties with an acid anhydride in the presence of a catalyst, e.g. acetic acid anhydride and N-methyl imidazole in tetrahydrofuran (THF) or acetonitrile (ACN).

(26) (iii) Oxidation of the resulting phosphite triester to the corresponding phoshoric acid triester by oxidizing agents such as I.sub.2/H.sub.2O in pyridine/THF (or ACN) mixtures.

(27) Step 2 in FIG. 4 is the deprotection reaction which removes not only the amino protecting group but simultaneously also removes all nucleobase and phosphate protecting groups and additionally cleaves the 5-amino modified oligonucleotide from the solid support. This reaction is carried out e.g. with ammonia or advantageously with methylamine or ammonia/methylamine mixtures (AMA) in water, in alcohol/water mixtures or in the gas phase. The removal of the diamide amino linker protecting group is triggered by deprotonation of an amide group, followed by intramolecular attack of the resulting nucleophilic deprotonated nitrogen at the neighbouring carbonyl group, formation of a tetrahedral intermediate and finally elimination of an amine and formation of a cyclic imide. This compound will react with another amine, e.g. methylamine, thereby forming again a N,N-dialkyl diamide, e.g. N,N-dimethyl phthalic diamide as shown exemplary in FIG. 5. All steps are fully reversible and therefore, a large excess of methylamine will lead finally to the formation of N,N-dimethyl phthalic diamide and the deprotected amino group of the 5 amino modified oligonucleotide XIII.

EXAMPLE 1

(28) a) Preparation of N-methyl-N-(-hydroxyalkyl)phthalic diamide -(2-cyanoethyldiisopropylphosphoramidite) (Formula IX): General procedure (see FIG. 3)

(29) To a solution of 0.1 mol N-(-hydroxyalkyl)phthalimide (Formula X) and 25.8 g (0.2 mol)N-ethyl-N,N-diisopropylamine in 400 ml dichloromethane was added slowly 30.7 g (0.13 mmol) 2-cyanoethyl diisopropylphosphoramidochloridite. After 2 h at 25, the reaction mixture was treated with H.sub.2O and stirred vigorously for 5 min. The phases were separated and the organic phase was dried (Na.sub.2SO.sub.4) and evaporated to dryness. The oily residue was subjected to silica gel chromatography (ethyl acetate/hexanes+2% Et.sub.3N as mobile phase). The intermediate (Formula XI) was dissolved in 200 ml MeOH and treated with 25 ml MeNH.sub.2 in EtOH (8 M, 0.2 mol). After 10 min at 25, the mixture was evaporated, dissolved in dichloromethane and extracted with H.sub.2O. After phase separation, the organic phase was dried (Na.sub.2SO.sub.4) and evaporated to dryness. The resulting solid product (Formula IX) was recrystallized from dichloromethane/hexanes and dried in vacuo. b) Preparation of N-methyl, N-(6-hydroxyhexyl)phthalic diamide 6-(2-cyanoethyl diisopropylphosphoramidite) Formula XIV (with a C.sub.6H.sub.12 linker)

(30) ##STR00019##

(31) Prepared according to the general procedure (see above) from 24.7 g N-(6-hydroxyhexyl)phthalimide [S. Neelakantan, I. Surjawan, H. Karacelik, C. L Hicks, P.A. Crooks, Bioorg. & Med. Chem. Lett. 2009, 5722]. Yield: 26.8 g (60%) as white solid (see FIG. 6A).

(32) .sup.1H-NMR (300 MHz, CDCl.sub.3): 7.57, 7.44 (2 m, 22 H, ArH); 6.94 (br. q, J=ca. 5 Hz, 1 H, NHMe); 6.85 (br. t, J=ca. 6 Hz, 1 H, NHCH.sub.2); 3.92-3.73 (m, 2 H, 2NCH(Me).sub.2); 3.73-3.53 (m, 4 H, 2CH.sub.2OP); 3.38 (q, J=ca. 7 Hz, 2 H, NHCH.sub.2); 2.94 (d, J=4.9 Hz, 3 H, NHCH.sub.3); 2.64 (t, J=6.5 Hz, 2 H, CH.sub.2CN); 1.70-1.53 (m, 4 H, 2CH.sub.2); 1.45-1.35 (m, 4 H, 2CH.sub.2); 1.19 (2 d, J=6.9, 12 H, 2C(CH.sub.3).sub.2). .sup.31P-NMR (121 MHz, CDCl.sub.3, .sup.1H-decoupled): 148.5. c) Preparation of N-methyl, N-(12-hydroxydodecanyl)phthalic diamide 12-(2-cyanoethyl diisopropylphosphoramidite) Formula XV (with a C.sub.12H.sub.24 linker)

(33) ##STR00020##

(34) Prepared according to the general procedure (see above) from 33.1 g N-(12-hydroxydodecyl)phthalimide [I. Sprung, A. Ziegler, S. L. Flitsch, Chem. Comm. 2002, 2676]Yield: 34.5 g (65%) as white solid (see FIG. 6B).

(35) .sup.1H-NMR (300 MHz, CDCl.sub.3): 7.54, 7.42 (2 m, 22 H, ArH); 7.05 (br. q, J=ca. 5 Hz, 1 H, NHMe); 6.90 (br. t, J=ca. 6 Hz, 1 H, NHCH.sub.2); 3.92-3.74 (m, 2 H, 2NCH(Me).sub.2); 3.72-3.51 (m, 4 H, 2CH.sub.2OP); 3.35 (q, J=ca. 7 Hz, 2 H, NHCH.sub.2); 2.93 (d, J=4.9 Hz, 3 H, NHCH.sub.3); 2.65 (t, J=6.8 Hz, 2H, CH.sub.2CN); 1.67-1.50 (m, 4 H, 2CH.sub.2); 1.41-1.24 (m, 16 H, 8CH.sub.2); 1.19 (2 d, J=6.8, 12 H, 2C(CH.sub.3).sub.2).sub.. .sup.31P-NMR (121 MHz, CDCl.sub.3, .sup.1H-decoupled): 148.5. d) Preparation of N-methyl, N-(11-hydroxy-3,6,9-trioxaundecanyl)phthalic diamide 11-(2-cyanoethyl diisopropylphosphoramidite) Formula XVI (with a CH.sub.2CH.sub.2OCH.sub.2CH.sub.2OCH.sub.2CH.sub.2OCH.sub.2CH.sub.2 linker)

(36) ##STR00021##

(37) Prepared according to the general procedure (see above) from 32.3 g N-(11-hydroxy-3,6,9-trioxaundecanyl)phthalimide [J. Kim, T. Morozumi, H. Nakamura, Org. Lett. 2007, 4419]. Yield: 32.9 g (63%) as white solid (see FIG. 6C).

(38) .sup.1H-NMR (300 MHz, CDCl.sub.3): 7.66, 7.53 (2 m, 21 H, ArH); 7.46 (m, 2 H, ArH); 7.00 (br. s, 1 H, NHMe and NHCH.sub.2); 3.92-3.53 (m, 20 H, 2NCH(Me).sub.2, 2CH.sub.2OP, NHCH.sub.2, 6CH.sub.2); 2.95 (d, J=4.7 Hz, 3 H, NHCH.sub.3); 2.64 (t, J=6.4 Hz, 2 H, CH.sub.2CN); 1.70-1.53 (m, 4 H); 1.45-1.35 (m, 4 H, 2CH.sub.2); 1.18 (2d, J=6.8, 12 H, 2C(CH.sub.3).sub.2). .sup.31P-NMR (121 MHz, CDCl.sub.3, .sup.1H-decoupled): 149.7.

EXAMPLE 2

(39) Experiment for the Determination of Stability Under Storage Conditions

(40) From Sigma-Aldrich a 250 mg sample of 6-amino-N-trifluoroacetyl-hexan-1-ol 1-(2-cyanoethyl diisopropylphosphoramidite) (Formula I) was ordered which arrived on dry ice. As soon as it arrived, the colorless, oily compound was stored at room temperature in the dark. At the same time, a solid 250 mg sample of N-methyl, N-(6-hydroxyhexyl)phthalic diamide 6-(2-cyanoethyl diisopropylphosphoramidite) Formula XIV (previously stored for 6 weeks at 20) was placed in an identical bottle and stored under identical conditions. After reaching room temperature, 20 mg of both compounds were withdrawn, dissolved in 0.7 ml CDCl.sub.3 and subjected to .sup.31P-NMR analysis (see FIG. 7). Immediately after withdrawal, the two bottles were capped and again stored at room temperature. After 1 day and 7 days, respectively, the same analysis was repeated (see FIG. 7). According to these measurements, the oily TFA-protected aminolinker phosphoramidite (Formula I) had a purity of 92%, 75% and 10% after t=0, 1 day and 7 days, respectively. In contrast, the solid pthalic diamide protected aminolinker phosphoramidite (Formula XIV) according to the present invention was completely stable for the duration of 7 days as revealed by .sup.31P-NMR analysis (121 MHz, CDCl.sub.3), measured after the indicated duration of storage at room temperature shown in FIG. 7.

EXAMPLE 3

(41) Experiment for the Determination of Deprotection Conditions

(42) ##STR00022##

(43) Samples of 50 mg N-methyl, N-(6-hydroxyhexyl)phthalic diamide were dissolved in 1 ml deprotection solution (as indicated in FIG. 8) and incubated under the variable conditions b), c) and d). After different time intervals, 0.1 ml aliquots were withdrawn, diluted with 0.6 ml D.sub.2O and analyzed by .sup.1H-NMR. The spectra were compared with those from a) the starting material and e) 6-amino hexanol, respectively (see FIG. 8).

(44) Almost quantitative deprotection within <30 min occurred at 20 under conditions c) and d), i.e. by 40% aq. MeNH.sub.2 and by 24% aq. NH.sub.3/40% MeNH.sub.2 1:1 (AMA), respectively. In contrast, a two-phase process was observed at condition b) by 24% aq. NH.sub.3 at 55: after 30 min 65% were deprotected and after 3 h 70%, respectively. Under these conditions, the direct elimination of the linker amine from the methyl substituted starting material (according to the upper processes in FIG. 5) seems to be fast, whereas the elimination of the linker amine from the NH.sub.2-derivative (obtained with ammonia according to the lower processes in FIG. 5) seems to be slow.

(45) FIG. 8 gives an overview over the results of the deprotection reaction under the tested conditions by .sup.1H-NMR spectroscopy (300 MHz) in D.sub.2O. Shown are partial spectra (1.0-4.0 ppm): a) Spectrum of starting material. b, c, d): Right sideSpectra of reaction mixtures, diluted with D.sub.2O and recorded after the indicated time; Left sidereaction conditions and results. e) Spectrum of the product. S: .sup.13C-satellite signals from the MeNH.sub.2 signal.

EXAMPLE 4

(46) Synthesis of a DNA Sequence with a 5-Amino Linker and its Conjugation to Digoxigenine

(47) ##STR00023## a) General: DNA assembly under standard conditions (see S. Pitsch, P. A. Weiss, L. Jenny, A. Stutz, X. Wu, Helv. Chim. Acta 2002, 84, p. 3773) on a Pharmacia Gene Assembler. Reagents and solvents from Sigma Aldrich; DNA phosporamidites, dG CPG solid support and activator (ethyl thiotetrazole) from Glen Research; analytical ion exchange HPLC conditions (see S. Pitsch, P.A. Weiss, L. Jenny, A. Stutz, X. Wu, Helv. Chim. Acta 2002, 84, p. 3773) (gradient 10-60% B in 12.5 min); ESI-MS from Finnegan. TEAA buffertriethylammonium acetate buffer pH 7.0; ACNacetonitrile. b) DNA synthesis: The DNA sequence 5-(aminolinker)AACAGCTATGACCATG-3 (Formula XVII) was assembled on a 0.2 mol synthesis scale. The final coupling was carried out with the amino linker building block N-methyl, N-(6-hydroxyhexyl)phthalic diamide 6-(2-cyanoethyldiisopropylphosphoramidite) Formula XIV (with a C.sub.6H.sub.12 linker) (c=0.07 M in ACN, 120 l). Deprotection was carried out with MeNH.sub.2 in H.sub.2O (12 M) for 75 min h at 35. After evaporation, the crude sequence Formula XVII (40 oD) was characterized by HPLC and ESI-MS (see FIG. 9, top). HPLC: t.sub.R 7.24 min (89%) ESI-MS: 5053.6 amu (calc. 5053.4 amu) c) Counterion exchange: An amount of 35 oD of the above described crude 5-aminolinker containing DNA sequence Formula XVII in the methylammonium form was loaded onto a C.sub.18-Sepak cartridge (Waters, pretreated with ACN and 0.2 M TEAA buffer). After washing with 5 ml 0.2 M TEAA buffer and 5 ml H.sub.2O, the product sequence was eluted with 2 ml ACN/H.sub.2O 1:1. After evaporation, 32 oD of the DNA sequence Formula XVII in the triethylammonium form were obtained. d) Conjugation: The above obtained 32 oD DNA sequence XVII in the triethylammonium form were dissolved in 50 l aqueous borate buffer (0.1 M, pH 8.4) and treated with a solution of 1 mg digoxigenine NHS ester (Sigma) in 100 l DMF. After 45 min at 30, the mixture was diluted with 0.9 ml H.sub.2O and subjected to desalting on a NAP 10 column (Pharmacia) according to the manufacturer's instructions. After evaporation, the crude digoxigenine labeled DNA sequence Formula XVIII (27 oD) was characterized by HPLC and ESI-MS. HPLC: t.sub.R 8.01 min (98%); ESI-MS: 5596.8 amu (calc. 5596.9 amu). FIG. 9 shows HPLC traces (left) and ESI MS spectra (right) of the crude 5-amino linker DNA sequence Formula XVII (top) and its crude digoxigenine conjugate Formula XVIII (bottom).

(48) Although preferred embodiments of the invention have been described using specific terms and devices, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit of the scope of the present invention, which is set forth in the following claims. In addition, it should be understood that aspects of various other embodiments may the interchanged both in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred version contained herein.