Dehydroaminobutyric acid

Methyl ester of M,M-bis(ferf-butoxycarbonyl)-(Z)-dehydroaminobutyric acid,[6] 1.58 g, 5 mmol... 

Figure 23.31 (a) Structures of kahalalides A-J. Bu, n-butanoic acid 2-MeBu, 2-methylbutanoic acid Zdhb, Z-dehydroaminobutyric acid 4-hypro,... 

A, B) The observation that the dehydroamino acids most frequently encountered are dehydroalanine and dehydroaminobutyric acid gives rise to the supposition that these are principally formed from serine, cysteine and threonine units by P-elimination reactions. A large number of P-eliminations have been carried out in vitro on S-methylcysteine, O-tosylserine and 0-phosphorylserine units incorporated in a peptide chain (cf. Section IV.A.2). 

Thermolysis of 3-alkylsulflnyl-a-amino acid derivatives is an alternative reaction which has been applied to the synthesis of dehydroamino acid compounds 325, 326). Esters and peptides with dehydroalanine, dehydroaminobutyric acid, dehydrovaline and dehydrophenylalanine units have in many cases been obtained in excellent yields. The method is especially suitable for peptides with base sensitive groups. The elimination appears to take place with particular facility in compounds in which the amino acid unit bearing the sulfoxide group is present as a tertiary amide 326). Dehydrophenylalanine and dehydroaminobutyric acid derivatives are formed as mixtures of Z- and E-isomers on sulfoxide elimination. 

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