Triterpene saponins of Maesa lanceolata leaves

Abstract

Chemical investigation of Maesa lanceolata leaves aqueous MeOH extract has led to the isolation of eight new triterpene glycosides identified as 16-oxo-28-hydroxyolean-12-ene 3- O - β -glucopyranosyl-(1'' → 6')- β -glucopyranoside 1 , 16 α , 28-dihydroxyolean-12-ene 3 - O - β -[(6''- O -galloylglucopyranosyl-(1'' → 2')][ β -glucopyranosyl-(1''' → 6')]- β -glucopyranoside 2, 16 α , 22 α , 28-trihydroxyolean-12-ene 3- O -[ β -glucopyranosyl-(1'' → 2')] [ α -rhamnopyranosyl- (1''' → 6']- β -glucopyranoside 3 , 22 α -acetyl-16 α -hydroxyolean-12-en-28-al 3- O -[ α -rhamnopyranosyl- (1''''  6''')- β -glucopyranosyl-(1'''  3')] [ β -glucopyranosyl-(1''  2')]- β -arabinopyranoside 4 , 22 α -acetyl-16 α ,21 β -dihydroxyoleanane-13 β :28-olide 3- O -[ β -glucopyranosyl-(1''' → 6')] [6''- O -coumaroylglucopyranosyl-(1'' → 2')]- β -glucopyranoside 5 , 16 α ,22 α -diacetyl-21 β - angeloyloleanane-13 β :28-olide 3 β - O -[ β -glucopyranosyl-(1'' → 2')][ β -glucopyranosyl- (1''' → 4')]- β -glucopyranoside 6 , 16 α , 22 α , 28-trihydroxy -21 β -angeloyloleanan-12-ene 3 β - O -[ α -rhamnopyranosyl-(1''' → 6'')][ β -glucopyranosyl -(1'' → 2')]- β -xylopyranoside 7 , 16 α , 28-dihydroxy-22 α -acetyl-21 β -angeloylolean-12-ene 3- O -[ β -galactopyranosyl-(1''  2')] [ α -rhamnopyranosyl-(1'''  4')]- α -arabinopyranoside 8 . Together with these were known compounds quercetin, myricetin, quercetin 3- O -rhamnopyranoside, myricetin 3- O - β -glucopyranoside, gallic acid, sistosterol 3- O - β -glucopyranoside, rutin, myricetin 3- O - α -rhamnopyranosyl-(1''  3')- β -glucopyranoside and quercetin 3,7- O - β -diglucopyranoside. Their structures were determined using spectros copic methods as well as comparison with data from known compounds. The in vitro antibacterial activity of aque ous MeOH extract of the leaves of M. lanceolata was also investigated and zone s of inhibition ranging from 28  0.1 to 10  0.2 mm were observed. The minimum inhibi tory concentration (MIC) for the extract ranged between 100 to 1000 μg/ml with the highest activity being observed with Vibro cholerae . Among the pure isolates, compound 6 was the most active and its highest recorded MIC value was 62.5 μg/ml