Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references
Betulin (lup-20(29)-ene-3β,28-diol) is an abundant naturally occurring triterpene. It is commonly isolated from the bark of birch trees and forms up to 30% of the dry weight of the extractive [1]. The purpose of the compound in the bark is not known. It can be converted to betulinic acid (the alcohol group replaced by a carboxylic acid group), which is biologically more active than betulin itself.
Betulinic acid and its synthetic analogues exhibit anti-malarial, anti-inflamatory and anti-HIV activity as well as showing cytotoxicity towards a number of tumour cell lines. Even though betulin derivatives are most widely studied for their anticancer activity, also the anti-HIV effect is quite well characterized and it has been demonstrated that betulins can inhibit HIV entry to T cells by binding to the gp41, a HIV protein needed for the invasion of the virus into the cell.
References
^Isolation of Betulin and Rearrangement to Allobetulin A Biomimetic Natural Product Synthesis Brian Green, Michael D. Bentley, Bong Y. Chung, Nicholas G. Lynch, and Bruce L. Jensen Journal of Chemical Education 1985 2007