Substrate-dependent dihydroxylation of substituted cyclopentenes: toward the syntheses of carbocyclic sinefungin and noraristeromycin.

Carbocyclic nucleosides are of considerable interest for the development of new therapeutic agents. A key reaction in the preparation of many such nucleoside analogues is dihydroxylation of appropriately substituted cyclopentenes. Although often considered a routine reaction, in this paper, we report the dramatic influence of substituents on the facial selectivity of dihydroxylations. The substituted cyclopentene substrates are derived from acylnitroso cycloaddition reactions of cyclopentadiene, followed by N-O reduction and efficient enzymatic resolution. The results are directly utilized in a very efficient asymmetric synthesis of an antiviral carbocyclic nucleoside, noraristeromycin 5. Extensions toward the synthesis of carbocyclic sinefungin 7 document the importance of realizing the substituent dependence of the dihydroxylation reaction.

Total synthesis of the cyclic heptapeptide Argyrin B: a new potent inhibitor of T-cell independent antibody formation.

[structure: see text] The total synthesis of Argyrin B (1) is presented using a synthetic plan that is convergent and flexible and conserves the stereogenic centers. The unusual amino acid 4-methoxy tryptophan (6) was obtained via an enzymatic resolution. Cyclization followed by oxidative elimination of the phenylseleno cysteine to the sensitive dehydroalanine afforded synthetic 1.