NH2-CH(CH3)-COOH + HO-CH(NH2)-CH2-COOH + HO-CH2-CH(NH2)-COOH → NH2-CH(CH3)-COO-CH(NH2)-CH2-COOH + H2O
NH2-CH(CH3)-COOH + HO-CH(NH2)-CH2-COOH + HO-CH2-CH(NH2)-COOH → NH2-CH(CH3)-COO-CH(NH2)-CH2-COOH + H2O