is a plant sterol, with only a small difference from cholesterol - an extra ethyl group
is a plant stanol, with only one small difference from sitosterol - a single bond rather than a double bond
on one of the rings.
As their names suggest, these compounds are alcohols, possessing an - OH group
which can react with acids to form esters.
Shown below is an ester of sitostanol - sitostanyl oleate.