TOTAL SYNTHESIS OF NATURAL AND ENT-FREDERICAMYCIN-A

A total synthesis of both enantiomers of the potent antitumor-antibiotic fredericamycin A (1) is detailed based on a room temperature inverse electron demand Diels-Alder reaction of a N-sulfonyl-1-aza-1,3-butadiene for assemblage of a pyridone F ring precursor, a single-step Michael addition-intramolecular acylation for annulation of the DE ring system onto this pyridone F ring precursor, implementation of a regiospecific chromium carbene benzannulation reaction for AB ring construction, and a simple aldol closure for introduction of the spiro CD ring system. Resolution of the penultimate precursor 41 followed by deprotection provided natural and ent-fredericamycin A. The indistinguishable cytotoxic potency of the two enantiomers (L1210 IC50, 0.03 and 0.04 mu g/mL, respectively) is disclosed along with that of the key partial structures 2 (IC50 = 2 mu g/mL) and 21 IC50 = 7 mu g/mL) constituting the fully functionalized ABCDE and DEF ring systems of the natural product.