Toward a Stable Apoptolidin Derivative: Identification of Isoapoptolidin and Selective Deglycosylation of Apoptolidin

[formula: see text] Isoapoptolidin was isolated from crude fermentation extracts of the apoptolidin-producing microorganism Nocardiopsis sp. Apoptolidin isomerizes to isoapoptolidin upon treatment with methanolic triethylamine to establish a 1.4:1 equilibrium mixture of isoapoptolidin and apoptolidin. Semisynthesis of a peracetylated and deglycosylated derivative of apoptolidin is also described.