Antimalarial and cytotoxic activities of pregnene-type steroidal alkaloids from Holarrhena pubescens roots

Abstract

The phytochemical investigation of an alkaloidal extract of Holarrhena pubescens roots led to the isolation and identification of a new pregnene-type alkaloid, mokluangin D (1), together with nine known steroidal alkaloids (2–10). The structure of the new metabolite was determined on the basis of spectroscopic analyses including 1D- and 2D-NMR spectroscopy and mass spectrometry. Compounds 3 and 4 showed potent antimalarial activity against Plasmodium falciparum K1 stain with IC₅₀ values of 1.2 and 2.0 μM, respectively, and showed weak cytotoxic activity against the NCI-H187 cell line with IC₅₀ values of 27.7 and 30.6 μM, respectively. The substituent groups at C-3 and the carbonyl group at C-18 are important for the activity against the P. falciparum K1 stain.

Keywords:

• Holarrhena pubescens
• pregnene-type steroidal alkaloids
• cytotoxicity
• antimalarial activity

Acknowledgements

University of Phayao was also acknowledged for laboratory facilities. We would like to thank Mr. Matin Van de Bult, Doi Tung Development Project, Chiang Rai, Thailand for plant identification and the bioassay laboratory, BIOTEC, NSTDA, Pathumthani, Thailand, for cytotoxic and antimalarial testing. TL thanks the Center of Excellence for Innovation in Chemistry (PERCH-CIC).