ABSTRACT
Two new cassane diterpenoids, 14ß-hydroxycassa-11(12),13(15)-dien-12,16-olide (1) and 6'-acetoxypterolobirin B (3), together with a known analogue, identified as 12α,14ß-dihydroxycassa-13(15)-en-12,16-olide (2), were isolated from the fruits of Pterolobium macropterum. Compound 1 is a cassane diterpenoid with a Δ11(12) double bond conjugated with an α,ß-butenolide-type, whereas compound 3 is a dimeric caged cassane diterpenoid with unique 6/6/6/6/6/5/6/6/6 nonacyclic ring system. The structures of 1 and 3 were characterized by extensive spectroscopic analysis combined with computational ECD analyses. The α-glucosidase inhibitory activity of isolated compounds was evaluated, and compounds 1 and 3 showed significant α-glucosidase inhibitory activity with IC50 values of 66 and 44 µM.
ABSTRACT
The isopimarane diterpene, 1α,11α-dihydroxyisopimara-8(14),15-diene (1), is the major constituents from the rhizomes of Kaempferia marginata (Zingiberaceae), a Thai medicinal plant. The microbial transformation of parent compound 1 by the fungus Cunninghamella echinulata NRRL 1386 gave five new metabolites, 7α,11α-dihydroxy-1-oxoisopimara-8(14),15-diene (2), 3ß,7α,11α-trihydroxy-1-oxoisopimara-8(14),15-diene (3), 7ß,11α-dihydroxy-1-oxoisopimara-8(14),15-diene (4), 7α-hydroxy-1,11-dioxoisopimara-8(14),15-diene (5) and 1α,7ß,11α-trihydroxyisopimara-8(14),15-diene (6), together with three known metabolites, 7-9. The structures of the new metabolites were elucidated by spectroscopic techniques. The known compounds were identified by comparison of the spectroscopic and physical data with those of reported values. The parent compound 1 and the metabolites have been neuroprotective activities evaluated against Aß25-35-induced damage in human neuroblastoma cells (SK-N-SH). Among them, compounds 1-3, 5 and 7-9 had significant neuroprotective activities at a concentration of 2.5 µM. The results demonstrated that these compounds might be worth for further development into therapeutic agents for the treatment of neurodegenerative diseases.