Roselipin 1A

The structures of roselipins 1A, 1B, 2A and 2B were elucidated by spectroscopic studies including 1H-1H COSY, 13C-1H COSY, 13C-1H HMQC and 13C-1H HMBC NMR experiments, and degradation experiments. They have the common skeleton of 2,4,6,8,10,12,14,16,18-nonamethyl-5,9,13-trihydroxy-2E,6E, 10E-icosenoic acid modified with a D-mannose and a D-arabinitol. Roselipin A and B groups were stereoisomers at the arabinitol moiety, which esterified the fatty acid from the different terminal hydroxy residue. Roselipin 2 group was 6"-O-acetyl roselipin 1 group.

Fungal roselipins, discovered as inhibitors of diacylglycerol acyltransferase (DGAT), consist of three parts; highly methylated C20 fatty acid, mannose and arabinitol. Demannosyl and/or dearabinitoyl roselipins were prepared chemically or enzymatically. Demannnosyl roselipins conserved the DGAT inhibitory activity, but the others lost the activity, indicating that the arabinitoyl fatty acid core is essential for eliciting the activity.

Gliocladium roseum KF-1040, a marine isolate, was found to produce a series of new inhibitors of diacylglycerol acyltransferase (DGAT). Four active compounds, designated roselipins 1A, 1B, 2A and 2B, were isolated from the fermentation broth of the producing strain by solvent extraction, ODS column chromatography and preparative HPLC. The highest production of roselipins was observed when cultured in the medium containing natural sea water. Roselipins inhibit DGAT activity with IC50 values of 15 approximately 22 microM in an enzyme assay system using rat liver microsomes.