On the use of carboxamidomethyl esters in the protease-catalyzed peptide synthesis

Carboxamidomethyl esters (CAM esters) ofZ- andBoc-protected alanine and phenylalanine were prepared in order to investigate their usefulness as substrates for -chymotrypsin- and papain-catalyzed hydrolysis and peptide synthesis reactions. The easy removal of theCAM-C-protecting group under mild conditions and dependent on the enzyme specificity was demonstrated. Examples are given for the protease-catalyzed synthesis of various peptide derivatives usingCAM esters as C- and N-components in aqueous-organic media. Comparatively short reaction times were observed. Abbreviations: IUPAC-IUB rules for peptides are followed, see Eur. J. Biochem. (1972) 27: 201.Ac = acetyl,Bz = benzoyl,Boc =tert-butyloxycarbonyl,Z = benzyloxycarbonyl, -OBu ^t =tert-butyl ester, -CAM = carboxamidomethyl ester,-OEt = ethyl ester, -OMe = methyl ester, TLC = thin layer chromatography.     

Structure investigations on assembled astaxanthin molecules

The carotenoid r,r-astaxanthin (3R,3′R-dihydroxy-4,4′-diketo-β-carotene) forms different types of aggregates in acetone–water mixtures. H-type aggregates were found in mixtures with a high part of water (e.g. 1:9 acetone–water mixture) whereas two different types of J-aggregates were identified in mixtures with a lower part of water (3:7 acetone–water mixture). These aggregates were characterized by recording UV/vis-absorption spectra, CD-spectra and fluorescence emissions. The sizes of the molecular assemblies were determined by dynamic light scattering experiments. The hydrodynamic diameter of the assemblies amounts 40 nm in 1:9 acetone–water mixtures and exceeds up to 1 μm in 3:7 acetone–water mixtures. Scanning tunneling microscopy monitored astaxanthin aggregates on graphite surfaces. The structure of the H-aggregate was obtained by molecular modeling calculations. The structure was confirmed by calculating the electronic absorption spectrum and the CD-spectrum where the molecular modeling structure was used as input.