| Summary: | 碩士 === 國立東華大學 === 化學系 === 90 === This thesis is to probe into enzyme-catalyzed transformation of aspartate, glutamate, asparagine, glutamine and their analogues to peptides or their derivatives. Initially, we found Novozyme 435 catalyzed the esterfication of (±)-benzoylmercaptosuccinic acid with methanol at 60℃. The conversion of (-)-benzoylmercaptosuccinyl -a-methyl ester was 59% within 48 hours. To confirm the steric structure, we synthesized dimethyl (+)-benzoylmercaptosuccinate from malic acid by chemical method to compare with that synthesized from Novozyme 435.
However, enzymatic coupling of benzoylmercaptosuccinic acid with L-phenylalanine methyl ester was unsuccessful. We turned to use (-)-acetylmercaptosuccinic anhydride to synthesized (-)-acetylmercaptosuccinyl-L-phenylalanine methyl ester. Thiolaspartame analogous was thus obtained after the deprotection of the acetyl group using NH3(aq).
We also discovered that the coupling of N-protected amino acids and cystine dimethyl ester were catalyzed by Aspergillus oryzae protease with 3.5 M, pH = 7.5 buffer. Monocoupled cystine-peptides were obtained (~40%) after 48 hours at 45℃. Bacillus licheniformis was able to catalyze the coupling of N-protected amino acid esters with cystine dimethyl ester. The conversion of these monocoupled cystine-peptide was as high as 56 % after 48 hours. Subsequently, Boc group was deprotected using HCl(aq) to obtain the asymmetric cytine-peptides.
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