Synthesis and Configuration of O-Acetyl Microgrewiapine A: Phantomization of O-Acetyl 6-epi-Microgrewiapine A.
Davies SG., Fletcher AM., Roberts PM., Taylor CE., Thomson JE.
The formation of O-acetyl microgrewiapine A is investigated. NMR data for the authentic sample derived from the natural product are corrected. Wholly synthetic samples, produced from reductive N-methylation of synthetic microcosamine A (to give synthetic microgrewiapine A) followed by O-acetylation, exhibit NMR data that are identical to those of the authentic sample. The previous report that this two-step transformation proceeds with epimerization at C-6 is thus shown to be in error: the purported sample of O-acetyl 6-epi-microgrewiapine A is structurally misassigned and is, in fact, O-acetyl microgrewiapine A. A plausible rationale for the structural misassignment is advanced.