Selektive enzymatische Schutzgruppenabspaltungen: Der n-Heptylester als Carboxylschutzgruppe in der Peptidsynthese

Enzymatic Removal of Carboxyl Protecting Groups. 1. Cleavage of thetert-Butyl Moiety

[reaction: see text] A recent discovery that a certain amino acid motif (GGG(A)X-motif) in lipases and esterases determines their activity toward tertiary alcohols prompted us to investigate the use of these biocatalysts in the mild and selective removal of tert-butyl protecting groups in amino acid derivatives and related compounds. An esterase from Bacillus subtilis (BsubpNBE) and lipase A from Candida antarctica (CAL-A) were identified as the most active enzymes, which hydrolyzed a range of tert-butyl esters of protected amino acids (e.g., Boc-Tyr-O(t)Bu, Z-GABA-O(t)Bu, Fmoc-GABA-O(t)Bu) in good to high yields and left Boc, Z, and Fmoc-protecting groups intact.

Effects of glycosylation on fragments of tumour associated human epithelial mucin MUC1

The glycodecapeptide AcPAPGS(alpha GalNAc)T(alpha GalNAc)APPA and the C-terminal glycohexapeptide AcS(alpha GalNAc)T(alpha GalNAc)APPA have been synthesized by applying the N-terminal Fmoc group in combination with the heptyl ester cleavable by lipase-catalyzed hydrolysis at pH 7. The solution conformation of these MUC1-related synthetic glycopeptides and the control, non-glycosylated decapeptide AcPAPGSTAPPA have been investigated using NMR spectroscopy. The structural studies indicate that the glycohexapeptide has a folded structure in solution. For this molecule, unrestrained molecular dynamics has been used to confirm the presence of the observed solution through-space connections. The results indicate that the non-globular nature of MUC1 is due to both protein core sequence and the effect of carbohydrate.

Synthesis of characteristic lipopeptides of the human N-Ras protein and their evaluation as possible inhibitors of protein farnesyl transferase

Lipopeptides carrying a farnesyl thioether or a palmitic acid thioester and a farnesyl thioether were prepared from S-farnesyl cysteine methyl ester by N-terminal extension of the peptide chain employing the base labile Fmoc blocking group of the palladium(0) sensitive Aloc urethane. By means of this technique a lipohexapeptide representing the completely functionalized, i.e. palmitoylated and farnesylated C-terminus of the human N-Ras protein, was prepared. If acid labile blocking functions like the Boc group were used, upon deprotection an undesired addition of the acid to the double bonds of the farnesyl residue occurred. Therefore, acid labile blocking groups should not be employed in the synthesis of farnesylated lipopeptides. The lipopeptide methyl esters which carry only a farnesyl group do not inhibit protein farnesyl transferase, whereas palmitoylated peptides are weak inhibitors of this enzyme.

Synthesis, characterization and preliminary crystallographic data of N6-(6-carbamoylhexyl)-FAD-D-amino-acid oxidase from pig kidney, a semi-synthetic oxidase

The FAD analogue, N6-(6-carboxyhexyl)-FAD, carrying a hexanoic acid residue at the N6 position of the adenine moiety was synthesized. A new semi-synthetic oxidase, N6-(6-carbamoylhexyl)-FAD-D-amino acid oxidase, was prepared by reacting the succinimido ester of N6-(6-carboxyhexyl)-FAD with apo-D-amino-acid oxidase from pig kidney in the presence of benzoate. Reaction conditions and methods have been developed for preparing pure semi-synthetic and fully active N6-(6-carbamoylhexyl)-FAD-D-amino acid oxidase that contains 1 covalently bound FAD analogue/subunit, as verified by redialysis, ultraviolet spectrophotometry, electrospray ionization (ESI)-MS and peptide mapping. Presumably, the N6-(6-carbamoylhexyl)-FAD moiety of this semi-synthetic D-amino-acid oxidase (DAAO), selectively bound to Lys163, has a structurally similar position to that of the non-covalently bound FAD of the native holoenzyme, since both DAAO forms show very similar kinetic properties (semi-synthetic DAAO, Vmax(app) = 17.7 mumol min-1 mg-1; KM(app) = 4.5 mM; native holo-DAAO, Vmax = 12.2 mumol min-1 mg-1; KM = 1.8 mM). Compared with the native holo-D-amino acid oxidase. this new semi-synthetic N6-(6-carbamoylhexyl)-FAD-D-amino acid oxidase is a considerably more stable enzyme that shows meso-thermostability and withstands inactivation on dilution. Probably, the lack of dissociation of FAD and, consequently, the absence of the instable apoenzyme are responsible for these phenomena. Preliminary investigations resulted in finding convenient and reproducible crystallization conditions for N6-(6-carbamoylhexyl)-FAD-D-amino acid oxidase. The single crystals, obtained by the sitting-drop method using ammonium sulfate as precipitant, belong to the tetragonal space group I422 with cell dimensions a = 16.3 nm, c = 13.6 nm. The crystals diffract to 0.3-nm resolution, with two molecules being present in the asymmetric unit, demonstrating the two-subunit quarternary structure of this semi-synthetic D-amino-acid oxidase.

Chemoselective Removal of Protecting Groups from O-Glycosyl Amino Acid and Peptide (Methoxyethoxy)ethyl Esters Using Lipases and Papain

The selective C-terminal deprotection of O-glycopeptide (methoxyethoxy)ethyl esters is achieved under mild conditions (pH 6.6, 37 degrees C) by enzymatic hydrolysis using papain or lipase M from Mucor javanicus to give building blocks useful for chain-extending glycopeptide synthesis. On the other hand, the selective removal of acetyl protecting groups from the saccharide portion of glycopeptides is accomplished by alternative enzymatic hydrolysis with lipase WG from wheat germ to furnish model substrates for enzymatic glycosyl transfer reactions in order to extend the carbohydrate side chain of these conjugates.