Amiaspochalasins A–H, Undescribed Aspochalasins with a C‑21 Ester Carbonyl from Aspergillus micronesiensis

Amiaspochalasins
A–H (1–8), eight undescribed
aspochalasins, and trichalasin D (9), a known analogue,
were isolated from the solid culture of Aspergillus
micronesiensis. Compounds 1–9 are aspochalasins with a C-21 ester carbonyl,
and their structures were determined by spectroscopic data, X-ray
crystallographic analyses, electronic circular dichroism calculations,
and chemical methods. The CH3-25 in compound 1 is located at C-16 rather than C-14 in the previously reported aspochalasins,
endowing 1 with an unexpected carbon skeleton. Compounds 2 and 3 are the first examples of aspochalasins
with an unprecedented 5/6/6/8 tetracyclic ring system. Compounds 4 and 5 are diastereomers of aspochalasins I
and J, respectively. Compounds 6 and 7 are
the first aspochalasins featuring a long open-chain system, and their
absolute configurations were discussed by comparing the NMR data of
the hydrolysis and methyl esterification products of 4 and 5. Compound 8 is an isomeride of 9. The cytotoxic and antimicrobial effects of 1–9 were tested.