Synthesis of chimera oligopeptide including furanoid β-sugar amino acid derivatives with free OHs: mild but successful removal of the 1,2-O-isopropylidene from the building block

Acetyl group for proper protection of β-sugar-amino acids used in SPPS

The synthesis of D-glucosamine-1-carboxylic acid based β-sugar amino acids (β-SAAs) is typically performed in nine consecutive steps via an inefficient OAc → Br → CN conversion protocol with low overall yield. Here, we present the improved and more efficient synthesis of both Fmoc-GlcAPC-OH and Fmoc-GlcAPC(Ac)-OH, β-SAAs consisting of only 4-5 synthetic steps. Their active ester and amide bond formation with glycine methyl ester (H-Gly-OMe) was completed and monitored by 1H NMR. The stability of the pyranoid OHs protecting the acetyl groups was investigated under three different Fmoc cleavage conditions and was found to be satisfactory even at high piperidine concentration (e.g. 40%). We designed a SPPS protocol using Fmoc-GlcAPC(Ac)-OH to produce model peptides Gly-β-SAA-Gly as well as Gly-β-SAA-β-SAA-Gly with high coupling efficiency. The products were deacetylated using the Zemplén method, which allows the hydrophilicity of a building block and/or chimera to be fine-tuned, even after the polypeptide chain has already been synthesized.

Advancement of the Cleavage Methods of Carbohydrate-derived Isopropylidene and Cyclohexylidene Ketals

Abstract:

Carbohydrates, amino acids, and nucleosides, the fundamental building blocks of complex biomolecules in nature, are essential starting materials for the fabrication of natural and unnatural structural entities, which necessitate the masking and demasking of various functional groups with the utmost chemoselectivity, mildness, and efficiency to avoid unintended bond breaking and formation, as well as associated reactions. Ketals, benzylidene, methoxymethyl, p-methoxybenzyl, silyl ethers, trityl, tert-butyl carbamate, and other functional groups are widely used in modern organic synthesis. In carbohydrate chemistry, the commonly used protecting functionality of isopropylidene and cyclohexylidene ketals necessitates effective methods for selective cleavage. This review summarises different methods for deblocking isopropylidene and cyclohexylidene ketals using inorganic acids, Lewis acid, silica-supported inorganic acids, Amberlite-120 (H+) resin, phosphotungstic acid, Nafion-H, NaBArF4.2H2O, montmorillonite clay, Dowex 50W-X8, camphorsulphonic acid (CSA), ceric ammonium nitrate, molecular iodine, ionic liquids, zeolites and so on.

Enantioseparation of ß2-amino acids by liquid chromatography using core-shell chiral stationary phases based on teicoplanin and teicoplanin aglycone

Enantioseparation of nineteen ß²-amino acids has been performed by liquid chromatography on chiral stationary phases based on native teicoplanin and teicoplanin aglycone covalently bonded to 2.7 µm superficially porous silica particles. Separations were carried out in unbuffered (water/methanol), buffered [aqueous triethylammonium acetate (TEAA)/methanol] reversed-phase (RP) mode, and in polar-ionic (TEAA containing acetonitrile/methanol) mobile phases. Effects of pH in the RP mode, acid and salt additives, as well as counter-ion concentrations on chromatographic parameters have been studied. The structure of selectands (ß²-amino acids possessing aliphatic or aromatic side chains) and selectors (native teicoplanin or teicoplanin aglycone) was found to have a considerable influence on separation performance. Analysis of van Deemter plots and determination of thermodynamic parameters were performed to further explore details of the separation performance.