Naeem B. Hanna

Fast cleavage and deprotection of oligonucleotides

Abstract We have developed methylamine/ammonia as a fast cleavage and deprotection reagent which effects complete cleavage of oligonucleotides from the solid support in 5 min at room temperature and complete deprotection in 5 min at 65°C. The problem of transamination side product formation, faced with the commonly used dCbz (10.0% side product) upon treatment with methylamine/ammonia, has been successfully solved by the use of dCac (0.0% side product). DMT dCac phosphoramidite --methylamine/ammonia system furnished oligonucleotides in equal or superior quality as compared to the other systems.

Ultrafast Cleavage and Deprotection of Oligonucleotides Synthesis and Use of CAc Derivatives

Abstract We have investigated the use of alkylamines as fast cleavage and deprotection reagents for the solid phase synthesis of oligonucleotides and found methylamine/ammonium hydroxide (or methylamine) as an efficient reagent. The transamination side product formed with the commonly used dCbz has been eliminated by the use of dCAc phosphoramidite. This system has successfully been used in the synthesis of oligonucleotides and oligonucleoside phosphorothioates. DMT dCAc hydrogen phosphonate and DMT ribo CAc-2′-O Me phosphoramidite also have been prepared and used in the synthesis of oligonucleotides.

Elimination of transamination side product by the use of dCAc methylphosphonamidite in the synthesis of oligonucleoside methylphosphonates

Abstract The transamination side product formed by the use of dC bz or dC ibu methylphosphonamidite upon treatment with ethylenediamine has been eliminated by the use of dC Ac methylphosphonamidite. The synthesis and characterization of DMT dC Ac methylphosphonamidite is described.

Synthesis of 2′,3′-Dideoxyribavirin

Abstract A synthesis of 1-(2,3-dideoxy-β-D-ribofuranosyl)-1,2,4-triazole-3-carboxamide (2′,3′-dideoxyribavirin, ddR) is described. Glycosylation of the sodium salt of 1,2,4-triazole-3-carbonitrile (5) with 1-chloro-2-deoxy-3,5-di-0-p-toluoyl-α-D-erythro-pentofuranose (1) gave exclusively the corresponding N-1 glycosyl derivative with β-anomeric configuration (6), which on ammonolysis provided a convenient synthesis of 2′-deoxyribavirin (7). Similar glycosylation of the sodium salt of methyl 1,2,4-triazole-3-carboxylate (2) with 1 gave a mixture of corresponding N-1 and N-2 glycosyl derivatives (3) and (4), respectively. Ammonolysis of 3 furnished yet another route to 7. A four-step deoxygenation procedure using imidazolylthiocarbonylation of the 3′-hydroxy group of 5′-0-toluoyl derivative (9a) gave ddR (11). The structure of 11 was proven by single crystal X-ray studies. In a preliminary in vitro study ddR was found to be inactive against HIV retrovirus.

Synthesis of Certain 5′-Substituted Derivatives of Ribavirin and Tiazofurin

Abstract The synthesis of several 5′-substituted derivatives of ribavirin (1) and tiazofurin (3) are described. Direct acylation of 1 with the appropriate acyl chloride in pyridine-DMF gave the corresponding 5′-O-acyl derivatives (4a-h). Tosylation of the 2′, 3′-O-isopropylidene-ribavirin (6) and tiazofurin (11) with p-toluenesulfonyl chloride gave the respective 5′-O-p-tolylsulfonyl derivatives (7a and 12a), which were converted to 5′-azido-5′-deoxy derivatives (7b and 12b) by reacting with sodium/lithium azide. Deisopropylidenation of 7b and 12b, followed by catalytic hydrogenation afforded 1-(5-amino-5-deoxy-β-D)-ribofuranosyl)-1, 2, 4-triazole-3-carboxamide (10b) and 2 - (5 -amino- 5-deoxy- β-D-ribofuranosyl) thiazole-4-carboxamide (16), respectively. Treatment of 6 with phthalimide in the presence of triphenylphosphine and diethyl azodicarboxylate furnished the corresponding 5′-deoxy-5′-phthaloylamino derivative (9). Reaction of 9 with n-butylamine and subsequent deisopropylidenation provided yet ano...

Synthesis of 5′-O-β-d-glucopyranosyl and 5′-O-β-d-galactopyranosyl derivatives of ribavirin

Abstract The synthesis of 5′- O -β- d -glucopyranosyl and 5′- O -β- d -galactopyranosyl derivatives ( 13 and 15 , respectively) of the antiviral agent ribavirin are descrobed. Direct glycosylation of 2′,3′- O -isopropylideneribavirin with either tetra- O -acetyl-α- d -glucopyranosyl bromide ( 4 ) or tetra- O -acetyl-α- d -galactopyranosyl bromide ( 8 ) under Koenigs-Knorr conditions ( i.e ., silver carbonate, silver perchlorate, and Drierite in dichloromethane) followed by O -deacetylation of the reaction product gave the corresponding ortho esters. However, treatment of 2′,3′-di- O -acetyl-5′- O -tritylribavirin ( 11 ) with 4 under the Bredereck modification of the Koenigs-Knorr reaction ( i.e ., silver perchlorate and Drierite in nitromethane) and subsequent deacetylation furnished the desired 1(5- O -β- d -glucopyranosyl-β- d -ribofuranosyl)-1,2,4-triazole-3-carboxamide ( 13 ). Similarly, reaction of 11 with 8 in the presence of AgClO 4 , and deprotection of the condensation product, gave 5′- O -β- d -galactopyranosylribavirin ( 15 ). The β-anomeric configuration of the d -glucosyl and d -galactosyl groups of 13 and 15 was assigned by 1 H-n.m.r. studies.