What is "betulin"

Betulin \Bet"u*lin\, n. [L. betula birch tree.] (Chem.) a term originally applied to a substance obtained as a resin or tar by extraction from the outer bark of the common European white birch ( Betula alba); now referring to the chemical compound ( C30H50O2) having a cyclopentanophenanthrene ring system, which is the main constituent of that extract, and which may be obtained crystalline; -- called also birch camphor.
--Watts.

n. (context biochemistry English) A naturally abundant triterpene, commonly isolated from the bark of birch trees, that can be converted to betulinic acid.

Betulin (lup-20(29)-ene-3β,28-diol) is an abundant, naturally occurring triterpene. It is commonly isolated from the bark of birch trees, where it forms up to 30% of the dry weight of the extractive, and is found in birch sap as well. 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.