Isolation of Cardenolide glycosides from Pergularia tomentosa.L and their Antioxidant activities

Abstract

Continuing our investigations on plants belonging to the Asclepiadaceae family, five known cardenolide glycosides (1-5), have been isolated from the aerial parts of P. tomentosa.L. The structures of these isolated compounds were identified by spectroscopic data as Uscharidin 1 which is isolated for the first time from Pergularia tomentosa.L, Calactin 2, 12 β-hydroxycalotropin 3, 6’-hydroxycalactin 4, and Galakinoside 5. The structures were elucidated by chemical and spectroscopic methods (2D-NMR, IR, and MS) and by comparison with the authentic samples (literature data). In addition, antioxidant activities of three cardenolide, the highest scavenging activity of DPPH, was observed in 2 (IC50= 1953 µg/ ml), followed by 4 (IC50= 3384 µg/ ml), and 3 (IC50= 3410 µg/ ml).

The family Asclepiadaceae is a very rich source of the cardenolide cardiac glycosides [1]. Pergularia tomentosa L. known locally as Ghalaka [2], a climbing to semierect perennial herb, belongs to the milkweed family [3]. Our previous work was concerned mainly with the isolation and characterization of new triterpene from the ethanolic extract [4]. Since cardenolides are active against a large range of cancer cell types [5, 6]. Previous studies reported the presence of the cardenolide glycosides ghalakinoside, calactin, uzarigenin, and pergularoside in the roots of Pergularia tomentosa L and desglucouzarin, coroglaucigenin, and uzarigenin along with a β-sitosterol glucoside in the leaves [1, 5], ghalakinoside was identified as a cytotoxic cardiac glycoside [2] and a potential antitumor agent [6, 7]. In our ongoing research for new compounds from medicinal plants from Algerian flora [8], we have investigated the ethanolic extract of the aerial parts of P. tomentosa.L. Here we report the occurrence of five known cardenolide glycosides uscharidin 1 [9], Calactin 2, 12β- hydroxycalotropin 3, 6’-hydroxycalactin 4, and Galakinoside 5. In this paper, we describe the antioxidant activities of three cardenolide 2- 4. The antioxidant capacity was evaluated by DPPH· radical.