In chemistry, esters are chemical compounds derived from an acid (organic or inorganic) in which at least one-OH (hydroxyl) group is replaced by an-O- alkyl (alkoxy) group. Usually, esters are derived from a carboxylic acid and an alcohol.Glycerides, which are fatty acid esters of glycerol, are important esters in biology, being one of the main classes of lipids, and making up the bulk of animal fats and vegetable oils.s a class, esters serve as protecting groups for carboxylic acids. Protecting a carboxylic acid is useful in peptide synthesis, to prevent self-reactions of the bifunctional amino acids. Methyl and ethyl esters are commonly available for many amino acids; the t-butyl ester tends to be more expensive.