摘要:
Chemical synthesis of the 1,2,3,4-tetrahydrophenanthrene 3,4-epoxide adducts resulting from benzylic, cis ring-opening of the epoxide by the exocyclic amino group of 2'-deoxyadenosine (dA) is described. The approach taken consists of coupling (+/-)-cis-3-hydroxy-4-amino-1,2,3,4-tetrahydrophenanthrene with a 6-fluoro analogue of dA in which the furanose hydroxyl groups are protected. The required amino alcohol was obtained by reaction of 1,2-dihydrophenanthrene with osmium tetraoxide to form the cis 3,4-diol, conversion to the trans chlorohydrin benzoate via its orthobenzoate, displacement of the benzylic chloride by azide, hydrolysis to the cis azido alcohol, and reduction to the racemic cis amino alcohol. Coupling of the amino alcohol with the 3',5'-bis-O-(tert-butyldimethylsilyl) derivative of 6-fluoro-9-(2-deoxy-beta-D-erythro-pentofuranosyl)purine results in a pair of diastereomers that are readily separated by HPLC on silica gel. Replacement of the previously used pyridine by 2,6-lutidine significantly improved the yield for the coupling step. Both adducts were acetylated on the hydroxyl group of the hydrocarbon and then desilylated on the sugar. Absolute configurations were assigned to the adducts on the basis of the shapes of their CD spectra. The 3S,4R diastereomer (derived from the more polar, late-eluting adduct) was blocked at the 5'-sugar hydroxyl group with the 4,4'-dimethoxytrityl group and allowed to react with 2-cyanoethyl N,N-diisopropylchlorophosphoramidite to produce the desired activated nucleoside. Incorporation into the deoxynucleotide TpGpA*pGpT as the central base proceeded in good yield with minor modifications to the standard DNA synthesizer protocol.