Solid Phase Synthesis of β-Peptides via Arndt-Eistert Homologation of Fmoc-Protected Amino Acid Diazoketones

Iterative One-Carbon Homologation of Unmodified Carboxylic Acids

The one-carbon homologation of carboxylic acids is a valuable route to construct families of homologues, which play fundamental roles in chemistry and biology. However, known procedures are based on multistep sequences, use harsh conditions or are limited in scope. Thus, almost a century after the discovery of the original Arndt-Eistert homologation sequence, a general method to directly convert carboxylic acids into their corresponding homologues remains elusive. Exploiting the photoredox reactivity of nitroethylene, we disclose a practical visible-light-induced homologation of unmodified carboxylic acids. Iterations of the procedure reveal an exceptionally tunable strategy for the construction of inert carbon spacers, opening new opportunities in synthesis.

Metal-free photocatalytic cross-electrophile coupling enables C1 homologation and alkylation of carboxylic acids with aldehydes

In contemporary drug discovery, enhancing the sp3-hybridized character of molecular structures is paramount, necessitating innovative synthetic methods. Herein, we introduce a deoxygenative cross-electrophile coupling technique that pairs easily accessible carboxylic acid-derived redox-active esters with aldehyde sulfonyl hydrazones, employing Eosin Y as an organophotocatalyst under visible light irradiation. This approach serves as a versatile, metal-free C(sp3)-C(sp3) cross-coupling platform. We demonstrate its synthetic value as a safer, broadly applicable C1 homologation of carboxylic acids, offering an alternative to the traditional Arndt-Eistert reaction. Additionally, our method provides direct access to cyclic and acyclic β-arylethylamines using diverse aldehyde-derived sulfonyl hydrazones. Notably, the methodology proves to be compatible with the late-stage functionalization of peptides on solid-phase, streamlining the modification of intricate peptides without the need for exhaustive de-novo synthesis.

One-carbon homologation of carboxylic acids via BtCH(2)TMS: a safe alternative to the Arndt--Eistert reaction

Carboxylic acids are converted into the corresponding homologated acids or esters, using easily available 1-(trimethylsilylmethyl)benzotriazole (1) as a one-carbon synthon. The effectiveness of the reaction has been investigated on six aryl and seven alkyl carboxylic acids.

Incorporation of conformationally constrained beta-amino acids into peptides

The use of norbornene units to induce the formation of beta-sheet and beta-turn type structures in peptides is discussed. The norbornene unit is readily prepared by a desymmetrization reaction and is easily incorporated into a peptide chain. Depending upon the exact nature of the norbornene unit, it is possible to form structures which resemble parallel beta-sheets, antiparallel beta-sheets or beta-turns. Similar peptide analogues incorporating a cis-2-amino-cyclopropane carboxylic acid unit can also be prepared. As an illustration of the application of this chemistry, a short, asymmetric synthesis of conformationally constrained metalloprotease inhibitors is presented.