Design and biosynthesis of dimeric alboflavusins with biaryl linkages via regiospecific C-C bond coupling.

Alboflavusins (AFNs) are a group of cyclohexapeptides with moderate antibacterial and antitumor activities from Streptomyces alboflavus sp. 313. In vivo and in vitro studies proposed that AFNs are biosynthesized by a non-ribosomal peptide synthetase machinery, and the 6-Cl-L-Trp precursor is supplied by a tryptophan halogenase gene locating outside the afn gene cluster. Guided by the structure-activity relationship knowledge about the AFN-like cyclohexapeptides, two Dimeric AFNs (Di-AFNs) with regiospecific biaryl linkages were designed and generated biotechnologically by expressing the P450 gene hmtS or clpS in S. alboflavus wild-type and mutant strains. The Di-AFNs displayed much better antibacterial and antitumor activities than their monomers as anticipated, exemplifying a rational strategy to generate natural product congeners with improved bioactivities.