New cytotoxic pregnane glycosides from Caralluma sinaica growing in Saudi Arabia

Certain species of genus Caralluma (Asclepiadaceae) are edible and form part of the traditional medicine system of many countries. Caralluma sinaica A.Berger, growing wild in the western region of Saudi Arabia, is used by locals as a remedy to treat diabetes [1]. Pregnane glycosides, the key phytochemical ingredients in Caralluma, are drawing much attention in recent years because of their antitumor and anticancer activities [2]. Thirteen pregnane glycosides, including six new (Fig.1), were isolated from the cytotoxic chloroform extract of the titled plant using repeated normal and reversed phase chromatographic techniques. The structures of the isolated compounds were characterized using extensive spectroscopic techniques including 1D and 2D microflowNMR methods for compounds available in restricted amount. A detailed profiling of the constituents was obtained by UHPLC-ESI-TOF/MS data [3]. Some isolated compounds were evaluated for their in vitro cytotoxic activity, and quinone reductase induction was also assessed.

Abbreviations: Benzoyl: Bz, Tigloyl: Tig, Acetate: Ac, Thevetose: Thev, Cymarose: Cym, Glucose: Glc, Digitalose: Dig.

Figure 1: Main structure of pregnane glycoside

List of new compounds

	R	R1	R2
1	Thev-(1→4)-cym-(1→4)-cym	Bz	Ac
2	Glc-(1→4)-cym	Tig	Ac
3	Glc-(1→4)- dig-(1→4)-cym-(1→4)-cym	Bz	Ac
4	Glc-(1→4)- thev-(1→4)-cym-(1→4)- cym	Bz	Ac
5	Glc-(1→4)-cym	Bz	Tig
6	Glc-(1→4)-cym-(1→4)-cym	Bz	Bz

Keywords: Caralluma sinaica, Asclepiadaceae, Pregnane glycosides, Cytotoxic

Acknowledgement: Acknowledgments: the authors thank Philippe Eugster and Dr. Laurence Marcourt for their help in the recording of the LC-MS profiles and NMR spectra respectively.

References: 1. Habibuddin M et al. (2008)J Ethnopharmacol 117: 215–220.

2.Abdel-Sattar A et al. (2009) Phytomedicine 16: 659–664.

3.Eugster P et al. (2011)J AOAC Int 94: 51–70.