Pseudo-Ring Methodology to Control the Conformations of Macrocyclic Peptides.

A pseudo-ring is a medium-sized cyclic structure, held together by a strong hydrogen bond, that can act as a mimetic of a covalently linked heterocycle. Molecules that contain pseudo-rings can switch between "open" and "closed" forms. This paper examines the utility of pseudo-ring constructs to control conformations and properties of macrocycles.

The Calcium-Dependent Antibiotics: Structure-Activity Relationships and Determination of Their Lipid Target.

The calcium-dependent antibiotics (CDAs) are a group of seven closely related membrane-active cyclic lipopeptide antibiotics (cLPAs) first isolated in the early 1980s from the fermentation broth of . Their target was unknown, and the mechanism of action is uncertain. Herein, we report new routes for the synthesis of CDA4b and its analogues, explore the structure-activity relationships at its lipid tail and at positions 3, 9, and 11, and determine the CDAs' lipid target.

Nitrilium ion trapping as a strategy to access structurally diverse heterobiaryl-containing peptide macrocycles.

Biaryl and heterobiaryl-containing cyclic peptides represent promising scaffolds for the development of bioactive molecules. The incorporation of heterobiaryl motifs continues to pose synthetic challenges, which is partially due to the difficulties in effecting late-stage metal-catalyzed cross-couplings. We report a new strategy to form heterobiaryls that is based on trapping nitrilium ions.

Solid-Phase Total Synthesis of Dehydrotryptophan-Bearing Cyclic Peptides Tunicyclin B, Sclerotide A, CDA3a, and CDA4a using a Protected β-Hydroxytryptophan Building Block.

A new approach to the synthesis of -dehydrotryptophan (ΔTrp) peptides is described. This approach uses Fmoc-β-HOTrp(Boc)(TBS)-OH as a building block, which is readily prepared in high yield and incorporated into peptides using solid-phase Fmoc chemistry. The -butyldimethylsilyl-protected indolic alcohol is eliminated during global deprotection/resin cleavage to give ΔTrp peptides exclusively as the thermodynamically favored Z isomer.

Synthesis of Fmoc-Protected Amino Alcohols via the Sharpless Asymmetric Aminohydroxylation Reaction Using FmocNHCl as the Nitrogen Source.

The aminohydroxylation of various alkenes using FmocNHCl as a nitrogen source is reported. In general, in the absence of a ligand, the reaction provided racemic Fmoc-protected amino alcohols with excellent regioselectivity but in low to moderate yields. However, in some instances, the yield of an amino alcohol product and the regioselectivity could be altered by the addition of a catalytic amount of triethylamine (TEA).