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The bacteria-specific membrane component lipid II is essential for bacterial cell wall synthesis. A tricyclic nisin mimic was designed and synthesized in which both thioether moieties were mimicked by an alkane-bridge, as well as the introduction of a third conformational constraint consisting of a macrocyclic lactam-bridge between the N-terminus and the B-ring. The newly designed tricyclic AB-ring mimic was found to bind lipid II since it was able to inhibit nisin-induced membrane leakage in a dose-dependent manner. These results imply that the tricyclic AB-ring mimic may form a novel class of lead structures for the development of nisin-based peptide antibiotics.

Tetrachloroethylene, or perchloroethylene (PCE), has considerable industrial use and is of toxicological interest because of a variety of effects. Most of the existing literature presents PCE oxide as a critical intermediate in the oxidative metabolism of PCE to Cl(3)CCO(2)H, oxalic acid, and products covalently bound to proteins, including trichloroacetyl derivatives of lysine. PCE oxide was synthesized by photochemical oxidation of PCE and characterized. Decomposition at neutral pH (t(1/2) = 7.9 min at 0 degrees C, 5.8 min at 23 degrees C, 2.6 min at 37 degrees C) yielded only trace ( approximately 1%) Cl(3)CCO(2)H; the major products identified were CO (73% yield) and CO(2) (63% yield). In phosphate buffer (0.10 M) a major product was identified as oxalyl phosphate. Oxalyl chloride also reacted to form CO and CO(2) in aqueous solution and to form oxalyl phosphate in neutral phosphate buffer. Oxalyl phosphate decomposed to oxalic acid (t(1/2) = 53 min at 37 degrees C) but did not react with lysine. Reaction of PCE oxide with free lysine yielded the oxalic acid amide derivatives of lysine plus lysine dimers in which cross-linking of the amino groups involved oxalo linkage. The reaction of PCE oxide with albumin yielded mainly N(6)-oxalolysine and some (5%) N(6)-trichloroacetyllysine. We propose a reaction pathway for PCE oxide based on our previous studies with trichloroethylene oxide, in which C-C bond scission is a major product of reaction in aqueous buffer and yields CO and CO(2). Oxalyl species are proposed as intermediates and prominent acylating species formed in the reactions of the epoxide. The formation of Cl(3)CCO(2)H in cytochrome P450 reactions is postulated to result from intramolecular migration within an enzyme intermediate.

An improved general method for automated synthesis of tripeptides was developed, in which methanesulfonic acid (MSA) was used in place of trifluoroacetic acid (TFA), thus making it possible to avoid, 1) corrosion of the apparatus by strong acid vapor, 2) formation of emulsions, and 3) use of the restricted solvent, dichloromethane. As an application of the automated synthesis apparatus, 216 fragment tripeptide derivatives were synthesized systematically using the MSA method, in excellent yield and with increased efficiency.

The picolinoyl group can be used as a convenient protective group for amines in peptide chemistry. Deprotection is performed by electrochemical reduction under mild acidic conditions.

An automated synthesis system, which is suitable for repetitive syntheses using similar reaction procedures, was used to synthesize systematically a library of all possible dipeptides (25) and tripeptides (125) from 5 protected amino acids. The apparatus has also been applied to the automated synthesis of 10 fragment tripeptide derivatives that are constituents of the hormone PACAP-27. The measured molecular optical rotation values of the library of 125 tripeptides were found to correlate well with calculated values obtained by summation of the molecular optical rotation values for the constituent amino acids.

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