Biotransformation of natural compounds. Oxido-reduction of Sch-642305 by Aspergillus ochraceus ATCC 1009

Sch-642305 is the major compound produced by the endophytic fungi Phomopsis sp. CMU-LMA. Incubation of Sch-642305 with Aspergillus ochraceus ATCC 1009 resting cells leads to three new derivatives through an oxido-reduction of the six-membered ring of the molecule. Reduction of the double bound leads to compound (1), which subsequently undergoes carbonyl reduction to (2) and ring hydroxylation to (3). According to the previously solved crystal structure of Sch-642305 coupled with ¹H NMR NOE correlation and the crystal structure of compound 1, the absolute configurations of the new derivatives were established. In contrast to the parent compound Sch-642305, compound (1) exhibits antimicrobial activity against Gram-negative bacteria. Furthermore, while all derivatives exhibit cytotoxic activity against various cancer cell lines, compound (2) achieved an IC₅₀ of 4 nM against human myelogenous leukemia K 562, compared to 20 nM for the parent Sch-642305.