10.1002/anie.200801652
The study reports the first total synthesis of (±)-trichodermamide B and a putative biosynthetic precursor to aspergillazine A using an oxaza-Cope rearrangement. Trichodermamides A and B are modified dipeptides isolated from a marine-derived fungus, with trichodermamide B showing significant in vitro activity against HCT-116 human colon carcinoma and moderate antimicrobial activity. The key chemical transformations involve the use of 3-benzyloxy-2,2-dimethoxy-3,5-cyclohexadienone (5) and vinylene carbonate in a Diels–Alder reaction to form the substrate for the oxaza-Cope rearrangement. Methyl ester 11 is obtained from the resultant compound 9 through several steps and serves as the substrate for the crucial nitrosation/oxaza-Cope rearrangement, yielding the desired oxazine 13. Further transformations, including allylic transposition and amide formation, lead to the synthesis of trichodermamide B. Additionally, the study explores the synthesis of the C5 thiol analogue of trichodermamides (21), proposed as a biosynthetic precursor to aspergillazine A, but finds that its cyclization to aspergillazine A is not spontaneous under various reaction conditions.