Pregnane glycosides from Hoodia gordonii
Graphical abstract
Pregnane glycosides (1, 2, 5–9) were isolated from the aerial parts of Hoodia gordonii. These constituents consisted of five pregnane derivatives namely hoodigogenin A, isoramanone, calogenin, and two unprecedented skeletons, hoodistanal and dehydrohoodistanal as the aglycones.
Introduction
Hoodia gordonii (Asclepiadaceae) is a succulent plant, indigenous to the summer rainfall regions of the Kalahari Desert in South Africa, Namibia, and Botswana. There are 13 reported species of the Hoodia genus, which have been a part of African food for centuries (Anonymous, 2007, Muller and Albers, 2002). Various uses of Hoodia have also been reported in African folklore such as for treatment of abdominal cramps, hemorrhoids, tuberculosis, diabetes, and as an aphrodisiac (Folden, 2008, Rubin et al., 2002). However, it has recently been known as an appetite suppressant (Anonymous, 2007, MacLean and Luo, 2004, Van Heerden et al., 1998, Van Heerden et al., 2007).
In our previous phytochemical studies on H. gordonii, we have reported the isolation and characterization of 11 new oxypregnane glycosides (hoodigosides A–K) (Pawar et al., 2007b), and 10 new calogenin glycosides (hoodigosides L–U) (Pawar et al., 2007a). These compounds were used as markers for developing HPLC, and LC–MS based methods for identification, and quality control of H. gordonii plant materials, and dietary supplements (Avula et al., 2006, Avula et al., 2007). Here we report the isolation, and characterization of seven new pregnane glycosides (1, 2, 5–9), along with three known compounds (3, 4, 10) (Schemes 2 and 3). These constituents were identified as the glycosides of hoodigogenin A, isoramanone, calogenin, and two novel chemotypes of aglycones, namely hoodistanal, and dehydrohoodistanal (Scheme 1). The structures of the isolates were identified by extensive spectroscopic and chemical studies.
Section snippets
Results and discussion
The CHCl3 extract of the aerial parts of H. gordonii was fractionated by multistep column chromatography to yield steroidal glycosides 1–10.
Based on the 13C NMR spectrum and HRESIMS m/z 1045.5711 for a sodiated molecular ion, the molecular formula for compound 1 was determined as C54H86O18. The presence of four sugar moieties was evident as its 1H NMR spectrum showed signals for four anomeric protons at δH 4.72 (d, J = 7.2 Hz), 4.94 (d, J = 11.2 Hz), 5.12 (d, J = 9.6 Hz), and 5.26 (d, J = 9.2 Hz), and
Concluding remarks
Previous phytochemical studies have shown that H. gordonii contains an abundance of pregnane glycosides, which comprise of hoodigogenin A, and calogenin as the aglycones (Dall’Acqua and Innocenti, 2007, Pawar et al., 2007a, Pawar et al., 2007b). Hoodigogenin A is an unique pregnane derivative from Hoodia, due to the tigloyl ester substitution at C-12. Although calogenin bisdesmosides have been reported from other plants in Asclepiadaceae family (Al-Yahya et al., 2000, Deepak et al., 1996,
General experimental procedures
NMR spectra were recorded on a Varian AS400 NMR spectroscope at 400 MHz (1H) and 100 MHz (13C). Proton and carbon chemical shift values are relative to internal standard TMS and were acquired in C5D5N and CDCl3. High-resolution mass spectra (positive) were acquired using electro-spray ionization (ESI) source, on an Agilent Series 1100 SL spectrometer. Optical rotations were measured on the Autopol IV polarimeter and specific rotations are expressed as deg.10.g−1.cm2. The ECD spectrum of compound 8
Acknowledgements
Part of the research was funded by “Botanical Dietary Supplements: Science-Base for Authentication” of the US Food and Drug Administration Grant No. FD-U-002071-07. The authors would like to thank Missouri Botanical Garden, USA for authentic plant material and Dr. V. Joshi for plant identification. The authors also thank Dr. B. Avula for assistance in acquiring the mass data. Y.J.S. is thankful to NCNPR for graduate research assistantship.
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2019, Studies in Natural Products ChemistryCitation Excerpt :Asclepiadaceae) is considered a subfamily of the Apocynaceae. Chemotaxonomially, the plant species show similarity too, and both Caralluma adscendens and Hoodia gordonii are rich in pregnane steroids [32,33]. Further chemotaxonomical screening of related species resulted in identification of further appetite suppressing pregnane glycosides in the roots of Cynanchum auriculatum Royle ex Wight [34].