Betulin (lup-20(29)-ene-3b,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. 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, an HIV protein needed for the invasion of the virus into the cell.
Recent clinical studies have verified that red alder (Alnus rubra) contains betulin and lupeol, compounds shown to be effective against a variety of tumors. Native Americans used red alder bark to treat poison oak, insect bites, and skin irritations. Blackfeet Indians used an infusion made from the bark of red alder to treat lymphatic disorders and tuberculosis.