Biotransformation of natural compounds: Unexpected thio conjugation of Sch-642305 with 3-mercaptolactate catalyzed by Aspergillus niger ATCC 16404 cells

► We investigate the bioconversion of the natural compounds Sch-642305. ► We isolate two unexpected thio-conjugation derivatives, difficult to access through chemical synthesis. ► We evaluate the antibiotic and cytotoxic activities of these compounds. ► We propose the reaction mechanisms involved.