Two pairs of undescribed enantiomers including a 2,5-diketopiperazine namely (+/-)-janthinolide G and a related analogue (+/-)-janthinolide H, were isolated from the crude extract of the fungus Penicillium griseofulvum together with five known compounds. Both two structures were determined by spectroscopic method and HRESIMS, whereas absolute stereochemistry was elucidated by using theoretical NMR calculation and ECD calculation. Janthinolide G is the first example of 2,5-diketopiperazine enantiomers with a cleavage diketopiperazine ring and comprises a terminal oxime group rarely seen in natural products. Biological screening of selected compounds found that 4 and 7 both exhibited weak alpha-glucosidase inhibitory effects, and a potential correlation was afforded by docking studies of alpha-glucosidase protein (PDB: 3TOP) and bioactive molecules. The plausible biosynthetic pathways of two unreported isolates are proposed here.
NSTL
Elsevier