合成路线1

In a further procedure, the prochiral diol (XX) was converted to the asymmetric mono-stearate ester (XXXII) employing vinyl stearate (XXXI) and lipase PS 30. After tosylation of alcohol (XXXII), the resulting diethoxy acetal (XXXIII) was hydrolyzed to aldehyde (XXXIV) employing different acidic catalysts. Reduction of aldehyde (XXXIV) to the corresponding alcohol (XXXV) was effected by means of catalytic hydrogenation over Ra-Ni or borane-tert-butylamine complex. Alcohol (XXXV) was further condensed with N-Cbz-L-valine (XVI), producing the diester tosylate (XXXVI). The analogous N-Boc- and N-Alloc-protected valine esters were similarly prepared. 6-Benzyloxy-2-aminopurine (XXXVII) was prepared by treatment of chloropurine (I) with benzyl alcohol and NaH or NaOH. Alkylation of purine (XXXVII) with tosylate (XXXVI) furnished adduct (XXXVIII), which was finally deprotected by catalytic hydrogenation. Optionally, tosylate (XXXVI) was condensed with chloropurine (I) to give (XXXIX). Hydrolysis of the chloropurine ring of (XXXIX) to the guanine derivative (XIII) employing either Et3N or HOAc, followed by catalytic hydrogenation as above, provided an alternative access to the title compound.