Labdane and norlabdane diterpenoids from the aerial parts of Leonurus japonicus

Abstract A new labdane diterpenoid, leojaponicin ( 1 ), a novel norlabdane, methyl 15,16-dinor-7-oxolabda-8-ene-14-oate ( 2 ), along with four known labdanes, hispanone ( 3 ), leoheteronins A ( 4 ) and B ( 5 ), 15-methoxyleoheteronin B ( 6 ), and three norlabdanes, 14,15,16-trinor-7-oxolabda-8-ene-13-oic acid ( 7 ), methyl 14,15,16-trinor-7-oxolabda-8-ene-13-oate ( 8 ), 14,15-dinor-8-labdene-7,13-dione ( 9 ), and a steroid, stigmast-4-ene-3-one ( 10 ), were isolated from a hexane extract of Leonurus japonicus . Their structures were determined using spectroscopic methods, mainly 1-D and 2-D NMR. Compounds 7 and 8 were previously semisynthesized but are reported here for the first time as naturally occurring compounds. In addition, α-glucosidase inhibitory activity of the isolated compounds was evaluated and compound 6 exhibited the strongest effect with IC 50 value of 26.7 μM (compared with the positive control acarbose, IC 50  = 214.5 μM).