Borinic acid catalysed peptide synthesis

Abstract

2-Chlorophenylborinic acid is reported to catalyze dipeptide synthesis in the presence of molecular sieves with no racemization.

Electron‐Deficient Borinic Acid Polymers: Synthesis, Supramolecular Assembly, and Examination as Catalysts in Amide Bond Formation

“…In the presence of molecular sieves (4 Å activated powder) and 10 mol % of catalyst 4 the amide 6 was obtained in moderate ( 4 a , 30 %) to high yield ( 4 b , 85 %) over two days in toluene at 65 °C. However, compared to the report by Blanchet the reaction required significantly higher temperature to achieve high yields. Next, we carried out the coupling reaction under the optimized conditions with the corresponding borinic acid polymers 3 as catalysts.…”

“…In addition, after an acid and base wash similar to that performed by Blanchet et al. in the workup of their reactions using the molecular borinic acid B (Figure ), the recovered polymers did no longer bear the borinic acid groups according to 1 H and 11 B NMR spectral analyses (Figures S66 and S67, Supporting Information). No 11 B NMR signal could be detected and in the 1 H NMR, the broad low‐field signals at 7.46, 7.30 ppm ( 3 a ) and 7.62, 7.52 ppm ( 3 b ) disappeared.…”

“…Electron‐deficient ortho ‐substituted boronic acids in particular have been found to be highly effective catalysts . More recently, Blanchet and co‐workers described the use of (molecular) borinic acids such as bis(2‐chlorophenyl) borinic acid ( B , Figure ) in the catalytic synthesis of peptides under mild conditions . Encouraged by their results, we envisioned that borinic acid‐supported polymers 3 may also show such catalytic properties.…”

“…Nevertheless, the estimated ratio (9:1) of styrene and 4‐trimethylstannyl styrene in 3‐Sn , as determined by integration of the signal of the methyl group at 0.32 ppm (9 n ) relative to the overlapping aromatic protons at 7.12–6.49 ppm (4 n +5 m ), was consistent with the monomer feed used in the reaction (9:1). The required aryldibromoboranes 2 were obtained by initially reacting commercially available arylboronic acids with trimethylorthoformate by using trifluoroacetic anhydride (TFA) as a catalyst, to form the corresponding arylborates 1 . Subsequent reaction with boron tribromide resulted in the formation of the respective aryldibromoboranes 2 , which were used directly after removal of volatiles under high vacuum .…”

“…The increased Lewis and Brønsted acid strength is anticipated to favor the formation of supramolecular aggregates via hydrogen bonding or Lewis acid‐base interactions as seen in the assembly properties of A . Inspired by the recently reported use of borinic acids, such as B , as catalysts for amide bond formation and various other chemical transformations, we also set out to explore the potential of highly electron‐deficient borinic acid polymers as supported catalysts.…”