70337-80-3

The contribution of hydrogen bonding to the stability of GA mismatches in RNA is investigated by making functional group substitutions. Such substitutions are made possible by the chemical synthesis of RNA; chemical incorporation of purine riboside and 2-

A simple treatment of fully aroylated purine and pyrimidine ribonucleosides with pulverized potassium tert-butoxide in tetrahydrofuran (THF) or dichloromethane under a controlled condition gave a mixture of the corresponding di-O-aroyl derivatives in which 2'-OH derivatives are preponderant over 3'-OH derivatives; 3',5'-di-O-benzoyluridine, N4,3',5'-tribenzoylcytidine, N4,3',5'-tri-O-toluoylcytidine, N2,3',5'-tribenzoylguanosine, and N2,isobutyryl-3',5'-di-O-benzoylguanosine were obtained crystalline in 80 percent, 78 percent, 72 percent, 67 percent, and 65 percent yields, respectively.

The syntheses of new monomeric building blocks for oligonucleotide synthesis via the phosphotriester approach containing the p-nitrophenylethyl group for phosphate and aglycone protection are described.Blocking of the amide function in guanosines at O6 can be achieved by the Mitsunobu reaction forming the corresponding O6-p-nitrophenylethyl derivatives (4,5,10).Sugar-protected thymidine (16) and uridine (17) have been alkylated at O4 in an SN1-type reaction by p-nitrophenylethyl iodide-silver carbonate in benzene to form the O4-p-nitrophenylethyl derivatives (18,19).Protection of the amino group in 2'-deoxycytidine (25) and cytidine (26) can be performed directly by 1-(p-nitrophenylethoxycarbonyl)-benzotriazole in DMF to obtain the corresponding carbamates (27,28) as a new type of N4-acylated cytidine derivative. p-Nitrophenylethoxycarbonylation of the amino group in 2'-deoxyadenosine (33) and adenosine (34) requires previous sugar protection by acyl or silyl groups and can then be achieved by p-nitrophenylethyl chloroformate or better by 1-methyl-3-p-nitrophenylethoxycarbonylimidazolium chloride to form N6-p-nitrophenylethoxycarbonyladenosines (38,39,40,42).The various p-nitrophenylethyl blocking groups are stable under mild hydrolytic conditions (e.g. ammonia and triethylamine) but can be cleaved selectively by DBU or DBN in aprotic solvents. 5'-O-Monomethoxytritylation (12,29,43) as well as phosphorylations at the 3'-OH group can be effected to give the corresponding 3'-(2,5-dichlorophenyl,p-nitrophenylethyl)-phosphotriesters (13,22,30,44) also in high yields.Oximate cleavage of the latter compounds to the phosphodiesters (14,24,32,46) and detritylation to the 5'-unblocked phosphotriesters (15,23,31,45) do not affect the aglycone protecting groups, thereby demonstrating their general versatility.The newly synthesized compounds have been characterized on the basis of their elementary analyses (C,N,H), and UV- and 1H-HMR-spectra.

The p-nitrophenylethyl group is introduced into the O6-position of 2'-deoxyguanosine and guanosine via the Mitsunobu-reaction to yield valuable building blocks for oligonucleotide syntheses.

The synthesis of aminoacylated 5'-O-(4-methoxytrityl)ribonucleosides of adenosine (1), guanosine (9), cytidine (31), uridine (17), and 5,6-dihydrouridine (23) have been optimized and these compounds (4, 12, 33, 18 and 24) silylated by tert-butyldimethylsilyl chloride.The corresponding 2'- and 3'-mono-O- as well as 2',3'-bis-O-(tert-butyldimethylsilyl) derivatives have been isolated by combination of chromatographical methods and fractional crystallization procedures in preparative scale.The characterization of the newly synthesized compounds was achieved by UV and 13C-NMR spectra.

Like hydrazine hydrate, hydroxylamine was found to be useful for the regioselective 2'-O-deacylation of fully acylated purine and pyrimidine ribonucleosides as its salt with acetic acid; the partial O-deacylation reactions (which were not accompanied by undesirable discolouration as happens with hydrazine hydrate) gave the corresponding di-O-acylribonucleosides in superior yields; e.g. 2',3'-di-O-benzoyladenosine (74percent yield), 3',5'- (64percent yield) and 2',5'-di-O-benzoyl-N6-benzyladenosine (63percent yield on performing the reaction in ethanol), N2,3',5'-tri-O-benzoylguanosine (66percent yield), N2,2',5'-tri-isobutyrylguanosine (48percent yield), and 3',5'-di-O-benzoyluridine (61percent yield) were obtained using hydroxylaminium acetate in pyridine.Treatment of fully acetylated ribonucleosides with an excess of hydroxylaminium acetate gave the corresponding 5'-O-acetylribonucleosides in quantitative yields.The excellent regioselectivity observed in the present partial O-decyclation was confirmed on the basis of chromatographic separation; the mixtures of di-O-acylribonucleosides, which had already been equilibrated in pyridine, were re-equilibrated on the silica gel during separation, e.g. a 70 : 30 mixture of 3',5'- and 2',5'-di-O-benzoyladenosine was completely converted into the former based on 1H n.m.r spectroscopy.The acetates of 9-β-D-xylo- and -arabino-furanosyladenine were also found to give predominantly the corresponding 3',5'-diacetates on hydroxylaminolysis.