SynopsisA conformational analysis of protected glutamate homo-oligopeptides 2-[Glu(OEt)],-OEt (n = 2-7) was carried out in chloroform solution using high-resolution 'H-nmr spectroscopy.At dilute peptide concentrations, the backbone NH and a-CH resonances are well resolved and can be assigned by combining extensive homonuclear decoupling experiments with data for co-oligopeptide derivatives. The structure of these peptides in solution was then assessed using information from chemical shifts, coupling constants, temperature coefficients, and titration of each oligomer with trifluoroacetic acid (TFA). The di-and tripeptides are found to be in disordered forms in deuterochloroform (CDC13) and CDCls/TFA mixtures. The tetrapeptide exhibits a folded structure with intramolecular hydrogen bonding at Glu2 in CDC13 and undergoes a transition to increasingly disordered forms as TFA is added. The pentamer to heptamer show a folded structure with a strong intramolecular hydrogen bond a t Glu2 and a weaker hydrogen bond at Glu3, which are disrupted as these peptides go to random coils a t high TFA/CDC13 ratios. In addition, the N-terminal portions of these glutamate peptides appear to be involved in side chain-main chain interactions. The results support the hypothesis that protected linear homo-oligopeptides may possess two or more segments of conformation with intramolecular folding preferred near the N-terminal portion.
SynopsisSeveral N-protected peptide amides, containing two aromatic residues spaced by one glycyl residue, have been enzymatically synthesized starting from P-Ar-OH and H-Gly-Ar-NH:! (P is the protecting group and Ar is the aromatic residue) and using wchymotrypsin as the catalyst for the coupling step. Reactions have been carried out in water solution, at room temperature, and afford yields ranging between 20 and 75% ca. This coupling reaction occurs in a much more restricted set of conditions than the hydrolysis reaction, e.g., only within a small pH range (ca. 6.5-7.5) and with particular buffering agents. The advantages and limitations of this type of reaction, compared with conventional coupling procedures, are discussed.
SynopsisThe syntheses of three series of glutamate oligopeptides attached to a macromolecular solubilizing polyoxyethylene (POE) group Boc-[Glu(OMe)],-OPOE, Ac-[Glu(OMe)],-OPOE, pGlu-[Gl~(0Me)]~~,-0POE ( n = 1-7) and their various analogs specifically deuterated a t individual a-CH positions using the liquid-phase method of peptide synthesis are described. It was shown that stepwise synthesis using the symmetrical anhydride gave homo-oligopeptides that are analytically pure. Fragment condensation methods using DCC-HOBt yield POE-peptides with POE-HOBt impurities but the peptide synthesis may be carried stoichiometrically with smaller quantities of amino acid derivatives. 360 MHz H-nmr conformational studies of these homo-oligopeptides in DMSO-4 are presented. The adeuterated peptides are shown to allow unequivocal homoligopeptide backbone NH assignments.
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