Triterpene and steroidal glycosides of the genus Melilotus and their genins. VI. Melilotoside A2 and adzukisaponin V from the roots of M. tauricus

Abstract

Two triterpene glycosides of the oleanane series, melilotoside A 2 and previously known adzukisaponin V, were isolated from the roots of Melilotus tauricus (L.) Pall. (Fabaceae). The structures of the glycosides were proved based on chemical transformations. Melilotoside A 2 Keywords: Melilotus tauricus, Fabaceae, adzukisaponin V, triterpene glycoside melilotoside A 2 .We have proved the structures of triterpene glycosides from the roots of Melilotus tauricus growing in Crimea. Chemical structures of a new triterpene glycoside called melilotoside A 2 (1) and the previously known adzukisaponin V (2) that was identified by us were established.An analysis of total acid hydrolysis products of each studied compound using PC and TLC (characterized by comparison of their chromatographic mobilities with authentic standards) showed the presence in each of the aglycon soyasapogenol B (3) (3E,22E,24-trihydroxyolean-12-ene). The aglycon was present in the native form in the CHCl 3 extract of the root extract of this plant.The carbohydrate part of melilotoside A 2 was glucuronic acid. This was confirmed by the presence in the 13 C NMR spectrum of the corresponding resonances (Table 1) [1]; in the IR spectrum, a band at 1740 cm 1 corresponding to a carboxylic C=O [2]. A comparison of the chemical shifts of glucoside C atoms in the unsubstituted portions with the literature showed that the carbohydrate constituent was bonded to C-3 of the aglycon (weak-field shift from 80.2 to 91.3 ppm [3]).Partial acid hydrolysis of 2 and chromatographic separation of the hydrolysis products isolated two progenins (2a and 2b). The TLC chromatographic mobility of progenin 2a coincided with that of 1. Total acid hydrolysis of the progenins and the glycoside showed according to PC the presence of glucuronic acid in 2a and glucuronic acid and glucose in 2b whereas glycoside 2 contained glucuronic acid, glucose, and rhamnose. Thus, the chemical structure of the glycoside sugar component consisted of sequential alternation of glucuronic acid, glucose, and rhamnose. Furthermore, progenin 2a was identical to 1 according to chemical transformations, TLC, and PC.The bond types in 2 were established by GC of the methanolysis products of the glycoside permethylate that was prepared by Hakomori methylation [4] and subsequent identification of methyl-3,4,6-tri-O-methyl-E-D-glucuronopyranoside; methyl-3,4,6-tri-O-methyl-E-D-glucopyranoside; and methyl-2,3,4-tri-O-methyl-D-L-rhamnopyranoside in the ratio 0.98:1.04:1.02.Thus, we propose for melilotoside A 2 the structure soyasapogenol B 3-O-E-D-glucuronopyranoside. Glycoside 2 was identified as adzukisaponin V {soyasapogenol B 3-O-[D-L-rhamnopyranosyl-(12)-E-D-glucopyranosyl-(12)-E-Dglucuronopyranoside]}.

Chemical constituents and cytotoxic activities of the extracts of Melilotus indicus

“…In Egypt, the leaf extract of M. indicus have been utilized as food additives for the prevention of many chronic diseases. The Melilotus species have been found to contain coumarins (Coumarin, dihydrocoumarin and coumarol), acids (o-Hydroxycinnamic, melilotic, coumarinic and o-coumaric), coumarin glycosides, fatty acids (Linoleic acid) and flavonoids (Quercetin and coumestrol), triterpenes (Melilotoside A2 and adzukisaponin V) as well as xylan [8,9]. Some of Melilotus species have been found to possess antioxidant and antibacterial properties [10,11].…”