Utilization of some non coded amino acids as isosters of peptide building blocks

Convergent Synthesis of Thioether Containing Peptides

Thioether containing peptides were obtained following three synthetic routes. In route A, halo acids esterified on 2-chlorotrityl(Cltr) resin were reacted with N-fluorenylmethoxycarbonyl (Fmoc) aminothiols. These were either cleaved from the resin to the corresponding (Fmoc-aminothiol)carboxylic acids, which were used as key building blocks in solid phase peptide synthesis (SPPS), or the N-Fmoc group was deprotected and peptide chains were elongated by standard SPPS. The obtained N-Fmoc protected thioether containing peptides were then condensed either in solution, or on solid support, with the appropriate amino components of peptides. In route B, the thioether containing peptides were obtained by the reaction of N-Fmoc aminothiols with bromoacetylated peptides, which were synthesized on Cltr-resin, followed by removal of the N-Fmoc group and subsequent peptide elongation by standard SPPS. In route C, the thioether containing peptides were obtained by the condensation of a haloacylated peptide synthesized on Cltr-resin and a thiol-peptide synthesized either on 4-methoxytrityl(Mmt) or trityl(Trt) resin.

Synthesis, Bioassay and NMR Study of Methyleneoxy Isosters of Oxytocin and Vasopressin

Syntheses of pseudodipeptides H-Tyrψ[CH2O]Ile-OH and H-Tyrψ[CH2O]Phe-OH were carried out using the intramolecular Williamson reaction of O-benzyltyrosinol with ethyl chloroacetate followed by N-protection and aldol reaction of the corresponding morpholin-3-one in position C2 with butanone or benzaldehyde, elimination of the hydroxy group to give derivatives with a double bond either as the E/Z (1 : 1) diastereomeric mixture in the case of the former derivative or as the Z-isomer only in the case of the latter one. Stereoselective hydrogenation and hydrolysis of both the lactams yielded the corresponding pseudodipeptides lacking the carbonyl group as a hydrogen bond donor. The introduction of the pseudodipeptides into positions 2 and 3 of oxytocin and vasopressin caused total absence of all biological activities in the formed analogues. The results of the bioassay and NMR study confirmed the importance of the H-bond between the backbone carbonyl of the Tyr2 and NH proton of the Asn5 residues for stabilization of the β-turn in the cyclic hexapeptide part of both the hormones and for their biological activity.

A useful route to (R)- and (S)-tert-leucine

Resolution of 1-(2-furyl)-2,2-dimethylpropylamine, an intermediate on a synthetic route to tert-leucine, followed by oxidation of the respective enantiomers, constitutes an interesting and useful strategy to (R)- and (S)-tert-leucine.