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Alpha-amino-beta-hydroxy-gamma-lactam 1 is a peptide mimic in which the Ser/Thr residue omega-, psi-, and chi-dihedral angle geometry all are constrained by the 5-membered lactam ring. Lactams 1 were made by employing N-(Fmoc)oxiranylglycine 3 as a bis-electrophile in TFE with cat. BzOH to sequentially alkylate and acylate a variety of amino acid derivatives in one pot. Solid-phase synthesis of beta-hydroxy-gamma-lactam 8, an analogue of the IL-1 modulator 101.10, was achieved using this method for studying Ser/Thr geometry.

The insertion of lactams into peptide analogs can enhance potency and improve receptor selectivity. The synthesis of lactam-bridged peptide sequences has been accomplished by a solid-phase approach on SynPhase lanterns using cyclic (R)- and (S)-oxathiazinane ester (2) to annulate the amino lactam residue onto the peptide chain. Parallel synthesis of alpha-amino gamma-lactam analogs of the allosteric modulator of IL-1 receptor 101.10 (D-Arg-D-Tyr-D-Thr-D-Val-D-Glu-D-Leu-D-Ala: rytvela) was performed by split-mix chemistry on the lanterns. In particular, the double insertion of alpha-amino gamma-lactams in the same peptide sequence has been accomplished by this effective method for the solid-supported combinatorial synthesis of lactam-bridged peptides. Peptides bearing an Agl residue exhibited curve shapes indicative of turn conformations in their circular dichroism spectra.

Incorporation of amino lactams into biologically active peptides restricts conformational mobility and may enhance selectivity and increase potency. alpha- and beta-amino gamma-lactams (Agl and Bgl), in both S and R configurations, were introduced into the growth hormone secretagogue GHRP-6 using a Fmoc-compatible solid-phase protocol relying on N-alkylation with five- and six-membered cyclic sulfamidates, followed by lactam annulation under microwave heating. Using this protocol in conjunction with IRORI Kan techniques furnished eleven new GHRP-6 analogs, and their binding affinity IC50 values on both the growth hormone secretagogue receptor 1a (GHS-R1a) and CD36 receptors are herein reported. The results indicate that selectivity towards one receptor or the other can be modulated by lactam substitution, typically at the Ala3 and the D-Phe5 positions.

Incorporation of amino lactams into biologically active peptides has been commonly used to restrict conformational mobility, enhance selectivity, and increase potency. A solid-phase method using a Fmoc-protection strategy has been developed for the systematic synthesis of peptides containing configurationally defined alpha- and beta-amino gamma-lactams. N-Alkylation of N-silyl peptides with five- and six-member cyclic sulfamidates 9 and 8 minimized bis-alkylation and provided N-alkyl peptides, which underwent lactam annulation under microwave heating. Employing this solid-phase protocol on the growth hormone secretagogue GHRP-6, as well as on the allosteric modulator of the IL-1 receptor 101.10, has furnished 16 lactam derivatives and validated the effectiveness of this approach on peptides bearing aliphatic, aromatic, branched, charged, and heteroatomic side chains. The binding affinity IC(50) values of the GHRP-6 lactam analogues on both the GHS-R1a and CD36 receptors are reported as well as inhibition of thymocyte proliferation measurements for the 101.10 lactam analogues. In these cases, lactam analogues were prepared exhibiting similar or improved properties compared with the parent peptide. Considering the potential for amino lactams to induce peptide turn conformations, the effective method described herein for their supported construction on growing peptides, and for the systematical amino lactam scan of peptides, has proven useful for the rapid identification of the secondary structure necessary for peptide biological activity.