A novel synthesis of K-13

Targeting Melanocortin Receptors Using SNAr-Type Macrocyclization: A Doubly Orthogonal Route to Cyclic Peptide Conjugates

While a range of strategies exist to accomplish peptide macrocyclization, they are frequently limited by the need for orthogonal protection or provide little opportunity for structural diversification. We have evaluated an efficient macrocyclization method that employs nucleophilic aromatic substitution (S_NAr) to create thioether macrocycles. This versatile macrocyclization, orthogonal to conventional peptide synthesis, can be performed in solution on unprotected peptidomimetics or on resin-bound peptides with side-chain protection in place. We show that the electron-withdrawing groups present in the products can be further utilized in subsequent orthogonal reactions to alter the peptide properties or to add prosthetic groups. The macrocyclization strategy was applied to the design of melanocortin ligands, generating a library of potent melanocortin agonists that exhibit distinct subtype selectivity.

Modifications of amino acids using arenediazonium salts

Aryl transfer reactions from arenediazonium salts have started to make their impact in chemical biology with initial forays in the arena of arylative modifications and bio-conjugations of amino acids, peptides and proteins.

Asymmetric synthesis of 3-azide-4-fluoro-l-phenylalanine

The asymmetric synthesis of N-Fmoc-protected 3-azide-4-fluoro-l-phenylalanine as a photoactive phenylalanine analog has been achieved by Schöllkopf's alkylation.

Exploiting the divergent reactivity of α-isocyanoacetate: multicomponent synthesis of 5-alkoxyoxazoles and related heterocycles

A novel multicomponent synthesis of 5-alkoxyoxazoles, based on a new reactivity profile of α-isocyanoacetates, is described. Thus, simply heating a solution of amine, aldehyde, and α-(EWG-phenyl)-α-isocyanoacetate or α-(4-pyridyl)-α-isocyanoacetate (EWG=electron-withdrawing group) in toluene provided 5-alkoxyoxazoles in good to excellent yields. Reaction of the 5-alkoxyoxazoles with various α,β-unsaturated acyl chlorides led to the formation of epoxytetrahydropyrrolo[3,4-b]pyridin-5-ones by a domino N-acylation/Diels-Alder cycloaddition sequence. Subsequent fragmentation under basic conditions provided 6,7-dihydro-5H-pyrrolo[3,4-b]pyridin-5-ones. A four-component synthesis of the pyridin-5-one compounds, without isolation of the 5-alkoxyoxazole, was subsequently developed.

On-resin macrocyclization of peptides via intramolecular SnAr reactions

On-resin macrocyclization via an SNAr reaction is employed in the synthesis of tocinoic acid analogs. Specifically, an N-terminal nitrofluorobenzene is attacked by a nucleophilic C-terminal sidechain. The remaining nitro group can be reduced and acylated. NMR is used to compare the conformation of the new macrocyclic peptides to tocinoic acid.