Bioacive compounds from Holarrhena curtisii PODS and Gymnema griffithii fruits

Abstract

In a phytochemical investigation of bioactive compounds from Apocynaceae family. Gymnemo griffrthii Craib. and Holorrheno curtisii King & Gamble. Were selected to investigate their phytochemical components. The chromatographic separation of methanolic extract of G. griffithii fruits was performed and led to the isolation of 8 new pregnane-type steroidal glycosides substituted with orthoacetate groups, named gymnemogriffithoside A-H. Their structures were established by spectroscopic analysis (1D and 2D NMR, HR-ESIMS and FTIR). The steroidal skeleton of gymnemogriffithoside A-F was deduced to be a dihydrosarcostin-8,14,18-orthoacetate while the steroidal skeleton of gymnemogriffithoside G and H was deduced to be a dihydrosarcostin-14,17,18-orthoacetate. The absolute stereochemistry of the steroidal skeleton of gymnemogriffithoside A was established as 35*, 55*, 85*, 9R*, 10S*, 12R*, 13R*, 14R*, 17S*, 20S* using both spectroscopic and Mosher’s Method. All eight steroidal glycosides isolated from G. griffithii fruits had two types of trisaccharide moieties, O-β-D-thevetopyranosyl-(14)-O-β-D-oleandroprodranosyl-(14- O-β-D-digitoxopyransyl and O-β-D-thevetopyranosyl-(14)- O-β-D-canaropyranosyl-(14)- O-β-D-digitoxopyransyl at the C-3 of their aglycones. All compounds were evaluated for their in vitro cytotoxic effects five human tumor cell lines (BT 474, Chago, Hep-G2, KATO-III and SW620). Gymnemogriffithoside C and F, containing a tigloyl moiety at C-20, showed a slight cytotoxicity against all tested cell lines in 40-70 µM, range while the others the were inactive at 100 µM, suggesting that the presence of the tigloyl moiety influenced the cytotoxic activity of the compounds in this type. In addition, the α-glucosidase inhibitory activity of all compounds was also tested. However, only aglycone of gymnemogriffithoside A and G showed moderate α-glucosidase inhibitory activity. The pods of H. curtisii provided 2 new tritepenoids identified as 3β-hydroxy-11α-hydroperoxyursan-12-en-28-oic acid and 3β-hydroxy-11α-hydroperoxyolean-12-en-28-oic acid along with 12 know compounds, squalene, α-amyrin acetate, β-amyrin acetate, lupeol acetate, lupeol, cycloeucalenol, 24-methylenpollinastanol, lanosta-7,24-dien-3β-Ol, ursolic acid, oleanolic acid, ( - )-catechin and ( - )-gallocatechin. All compounds, except squalene, were evaluated for their α-glucosidase inhibitory activity. Among of them, ursolic acid, oleanolic acid, 3β-hydroxy-11-α-hydroperoxyursan-12-en-28-oic acid and 3β-hydroxy-11-α-hydroperoxyursan-12-en-28-oic acid, processed with pentacyclic triterpenoid acid skeleton showed significant α-glucosidase inhibitory activity in the range of 10-80 µM comparable to standard control acarbose (IC₅₀ = 884.6 µM).