AbstractComplementary to hydrophobic five membered ring β-amino acids (e.g. ACPC), β-sugar amino acids (β-SAAs) have found increasing application as hydrophilic building blocks of foldamers and α/β chimeric peptides. Fmoc-protected β-SAAs [e.g. Fmoc-RibAFU(ip)-OH] are indeed useful Lego elements, ready to use for SPPS. The removal of 1,2-OH isopropylidene protecting group increasing the hydrophilicity of such SAA is presented here. We first used N3-RibAFU(ip)-OH model compound to optimize mild deprotection conditions. The formation of the 1,2-OH free product N3-RibAFU-OH and its methyl glycoside methyl ester, N3-RibAFU(Me)-OMe were monitored by RP-HPLC and found that either 50% TFA or 8 eqv. Amberlite IR-120 H+ resin in MeOH are optimal reagents for the effective deprotection. These conditions were then successfully applied for the synthesis of chimeric oligopeptide: -GG-X-GG- [X=RibAFU(ip)]. We found the established conditions to be effective and—at the same time—sufficiently mild to remove 1,2-O-isopropylidene protection and thus, it is proposed to be used in the synthesis of oligo- and polypeptides of complex sequence combination.
The reaction of 7-chloro-1-cyclopropyl-6-fluoro-8-nitro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (7) with each of sarcosine and (±)-pipecolinic acid afforded the corresponding N-(4- oxoquinolin-7-yl)-α-amino acids 8 and 9. Reductive lactamization of the latter with sodium dithionite gave hexahydropyrido[2,3- f ]quinoxaline (10) and octahydrodipyrido[1,2-a : 2,3- f ]quinoxaline (11) derivatives, respectively. Compounds 8 - 11 and their homologs 1 - 6, accessible from (S)-proline, (2S, 4R)-4-hydroxyproline and (S)-tetrahydroisoquinoline-3-carboxylic acid exhibit good to excellent antibacterial activities against E. coli and S. aureus.
The synthesis of the tetrapeptide, N-t-butoxycarbonyl-ε-N-carbobenzoxy-L-lysylglycyl-ε-N-carbobenzoxy-L-lysylglycine 4-(methylthio)phenyl ester is described. The utility of this protective ester is shown by its easy conversion to the protected tetrapeptide 4-(methylsulfonyl)phenyl activated ester without decomposition. Removal of the N-butoxycarbonyl protecting group afforded the polymerizing unit, ε-N-carbobenzoxy-L-lysylglycyl-ε-N-carbobenzoxy-L-lysylglycine 4-(methylsulfonyl)phenyl ester. Polymerization of this material on the partially blocked monomer glycine-1-C14 ethyl ester hydrochloride, at a relatively high dilution, gave poly-(ε-N-carbobenzoxyl-L-lysylglycyl)glycine-1-C14 ethyl ester. The carbobenzoxy protective groups were removed to give the title compound.
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