摘要：

The construction of carbocyclic nucleosides with a fixed E-3 ring pucker in the Southern hemisphere of the pseudorotational cycle is achieved from a common precursor carbocyclic amine, (1S,3S,4R,5S)-3-benzyloxy-4-benzyloxymethyl- 1-aminobicyclo[3.1,0]hexane 20. This carbocyclic amine is efficiently assembled from optically pure 2-benzyloxymethylcyclopent-3-enol 11 in ten steps. The key cyclopropanation step is performed on (3R,4S)-1-cyano-4-benzyloxy-3-(benzyloxymethyl)cyclopentane 15, and proceeds regio- and stereo-selectively to give the critical cyanocarbocyclic intermediate 17 from which the amine 20 is subsequently obtained. Synthesis of the pyrimidine analogues 6-8 is accomplished via the intermediate acyclic acryloylureas 21 and 22. Preparation of purines 9 and 10 required prior N-formylation of the corresponding 4,6-dichioro-5-aminopyrimidine and 4,6-dichloro-2,5-diaminopyrimidine heterocyclic precursors for efficient coupling with amine 20. Except for (S)-2'-deoxy-methanocarba-A (9, the 2'-deoxyadenosine analogue), all Southern conformers appear to be devoid of antiviral activity.

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