Tetramethyl orthosilicate (TMOS) is shown to be an effective reagent for direct amidation of aliphatic and aromatic carboxylic acids with amines and anilines. The amide products are obtained in good to quantitative yields in pure form directly after workup without the need for any further purification. A silyl ester as the putative activated intermediate is observed by NMR methods. Amidations on a 1 mol scale are demonstrated with a favorable process mass intensity.

A library of peptides and glycopeptides containing (4R)-hydroxy-L-proline (Hyp) residues were designed with a view to providing stable polyproline II (PPII) helical molecules with antifreeze activity. A library of dodecapeptides containing contiguous Hyp residues or an Ala-Hyp-Ala tripeptide repeat sequence were synthesized with and without α-O-linked N-acetylgalactosamine and α-O-linked galactose-β-(1→3)-N-acetylgalactosamine appended to the peptide backbone. All (glyco)peptides possessed PPII helical secondary structure with some showing significant thermal stability. The majority of the (glyco)peptides did not exhibit thermal hysteresis (TH) activity and were not capable of modifying the morphology of ice crystals. However, an unglycosylated Ala-Hyp-Ala repeat peptide did show significant TH and ice crystal re-shaping activity suggesting that it was capable of binding to the surface of ice. All (glyco)peptides synthesized displayed some ice recrystallization inhibition (IRI) activity with unglycosylated peptides containing the Ala-Hyp-Ala motif exhibiting the most potent inhibitory activity. Interestingly, although glycosylation is critical to the activity of native antifreeze glycoproteins (AFGPs) that possess an Ala-Thr-Ala tripeptide repeat, this same structural modification is detrimental to the antifreeze activity of the Ala-Hyp-Ala repeat peptides studied here.

The first total syntheses of the marine sponge-derived cyclic depsipeptide natural products Polydiscamides B, C, and D are described. The molecules were constructed through the convergent fusion of cyclic and linear fragments via an unprecedented native chemical ligation-oxidation protocol.

The efficient synthesis of homogeneous MUC1 peptide oligomers using sequential ligation reactions in the N-to-C and C-to-N directions is reported. The bi-directional ligation strategy makes use of thioester formation via N → S acyl shift chemistry in combination with peptide ligation reactions and was used to prepare a library of peptide oligomers ranging in molecular mass from 3.8-9.4 kDa, comprised of between 2 and 5 repeats of the MUC1 variable number tandem repeat sequence.

Efforts toward the total synthesis and stereochemical assignment of the cyclic depsipeptide natural product microspinosamide are described. A single diastereoisomer was targeted corresponding to the predicted structure of the natural product incorporating a (2S, 3R)-β-hydroxy-p-bromophenylalanine residue. Assembly was achieved through the initial synthesis of a cyclic depsipeptide and a linear peptide thioester fragment by solid-phase peptide synthesis, followed by fusion of the two fragments through a native chemical ligation–oxidation protocol. Extensive spectroscopic analysis showed structural differences to the isolated natural product, suggesting that a diastereoisomer of microspinosamide had been synthesised. This work lays the foundation for the future synthesis of the correct diastereoisomer.

We report an improved total synthesis of 4,5dibromo-9,10-dihydrophenanthrene-2,3,6,7-tetraol, (±)-polysiphenol, via intermolecular McMurray dimerization of 5-bromovanillin and subsequent intramolecular oxidative coupling as the key steps. The synthetic route is applicable to 4,5-dichloro-and 4,5-difluorohalologues (as well as a 4,5-dialkyl-analogue). Distinctive AA′BB′ multiplets in their 1 H NMR spectra for the dimethylene bridges of the dibromo and dichloro compounds reveal them to be roomtemperature stable atropisomers, while for the difluoro compound they present as a singlet. X-ray crystal structure determinations of their tetramethylated synthetic precursors show atropisomeric twist angles of 48°, 46°, and 32°, respectively, with the former representing the largest yet observed in any 4,5-disubstituted-9,10dihydrophenanthrene. DFT computational studies reveal an unprecedented two-stage atropisomeric interconversion process involving time-independent asynchronous rotations of the dimethylene bridge and the biaryl axis for halologues containing chlorine or bromine, but a more synchronous rotation for the difluoro analogue.