11027-17-1 15005-62-6 Bottromycic A2 acid, methyl ester Bottromycin A(2) Bottromycin A2 I 337B cis-3-Methyl-L-prolyl-L-valyl-N1-(carboxymethyl)-3-methylvalinimidoyl-3-methylvalyl-beta-methylphenylalanyl-3-(2-thiazolyl)-beta-alanine 6-methyl ester cyclic (3-1)-peptide stereoisomer