Botryane terpenoids produced by Nemania bipapillata an endophytic fungus isolated from red alga Asparagopsis taxiformis - Falkenbergia stage

摘要

A chemical study of the EtOAc extract of Nemania bipapillata (AT-05), an endophytic fungus isolated from the marine red alga Asparagopsis taxiformis - Falkenbergia stage, led to the isolation of five new botryane sesquiterpenes, including the diastereomeric pair (+)-(2R,4S,5R,8S)-(>1) and (+)-(2R,4R,5R,8S)-4-deacetyl-5-hydroxy-botryenalol (>2), (+)-(2R,4S,5R,8R)-4-deacetyl-botryenalol (>3), one pair of diastereomeric botryane norsesquiterpenes bearing an unprecedented degraded carbon skeleton, (+)-(2R,4R,8R)-(>4) and (+)-(2R,4S,8S)-(>5), which were named nemenonediol A and nemenonediol B, respectively, in addition to the known 4β-acetoxy-9β,10β,15α-trihydroxyprobotrydial (>6). Their structures were elucidated using 1D and 2D NMR, HRESIMS and comparison with literature data of similar known compounds. The absolute configurations of >2, >3 and >4 were deduced by comparison of experimental and calculated electronic circular dichroism (ECD) spectra, while those of >1 and >5 were assigned from vibrational circular dichroism (VCD) data. Compound >4 weakly inhibited acetylcholinesterase, whereas compound >1 inhibited both acetylcholinesterase and butyrylcholinesterase. Compounds >1, >3, >5 and >6 were tested against two carcinoma cell lines (MCF-7 and HCT-116), but showed no significant citotoxicity at tested concentrations (IC50 > 50 µM).