Cassane diterpenoids with α-glucosidase inhibitory activity from the fruits of Pterolobium macropterum

Two new cassane diterpenoids, 14β-hydroxycassa-11(12),13(15)-dien-12,16-olide ( 1 ) and 6′-acetoxypterolobirin B ( 3 ), together with a known analogue, identified as 12α,14β-dihydroxycassa-13(15)-en-12,16-olide ( 2 ), were isolated from the fruits of Pterolobium macropterum . Compound 1 is a cassane diterpenoid with a Δ 11(12) double bond conjugated with an α,β-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 IC 50 values of 66 and 44 μM.