New antimicrobial agents acting on bacterial cell walls.

摘要

Two approaches were undertaken to study potential inhibitors of peptidoglycan biosynthesis. Three types of compounds were designed as potential inhibitors of glycosyltransferase, a key enzyme for the formation of bacterial cell wall. Syntheses of α-C-glycosides and disaccharide analogs of lipid II were unsuccessful. Target O-(dimethyl ( Z)-2-oxymethyl-3-octylbutenedioate) 2-acetamido-3,4,6-tri- O-acetyl-2-deoxy-β-D-glucopyranoside ( 81) was prepared by coupling dimethyl (Z)-2-hydroxymethyl-3-octylbutenedioate (73) and phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-tetrachlorophthalimido-1-thio-β- D-glucopyranoside (52) (4 steps, 36% overall yield). (Z)-2-(2-Acetamido-2-deoxy-α-D-glucopyranosyl)oxymethyl-3-tetradecylbutenedioic acid dilithium salt (98) was synthesized from 3,4,6-tri- O-acetyl-2-azido-2-deoxy-α-D-glucopyranosyltrichloroacetimidate (85) and dimethyl (Z)-2-hydroxymethyl-3-tetradecylbutenedioate (74) (7 steps, 22% overall yield). Chaetomellic acid A dilithium salt (13), (Z)-2-geranyl-3-methylbutenedioic acid dilithium salt (14), (Z)-2-farnesyl-3-methylbutenedioic acid dilithium salt (15) and ( Z)-2-nerolyl-3-methylbutenedioic acid dilithium salt (16) were prepared by conjugate addition to dimethyl acetylenediacarboxylate followed by ester hydrolysis (72–81% overall yield). Compounds 13–16 were tested as inhibitors for rubber transferases from Hevea brasiliensis and Parthenium argentatum. No inhibition was observed for compounds 14 and 16. Compound 13 is a competitive inhibitor of H. brasiliensis and P. argentatum ( K_i = 42 μM and 8.8 μM, respectively). Compound 15 is a competitive inhibitor of P. argentatum ( K_i = 25 μM) and a non-competitive inhibitor of H. brasiliensis (K_i = 140 μM).; Bacteriocins were also studied as potential inhibitor of peptidoglycan biosynthesis. Piscicolin 126, carnobacteriocins B1 and BM1, and a new bacteriocin were isolated from Carnobacterium piscicola 307 and 682, characterized by mass spectrometry and amino acid sequencing. Brochothrix campestris ATCC 43754 produces a two-component bacteriocin, brochocin C (BrcC). An improved purification method was developed for BrcC using n-butanol and chloroform extraction. Mass spectral characterization of the two components, BrcA and BrcB, showed that both are excreted into the medium by B. campestris as mature peptides (59 and 43 amino acids, respectively). Separate expression clones of both peptides had been constructed in C. piscicola LV17C, but the products had not been chemically characterized. Purification by the new protocol showed that BrcA is expressed as the mature peptide, but that BrcB is produced by C. piscicola as a fragment, BrcB(10–43), which has been cleaved at an internal Gly-Gly site. In combination with BrcA, this fragment displays the full activity of the BrcC complex. Circular dichroism measurements revealed a high β-sheet content in the secondary structure of both peptides, as well as in a 1:1/BrcA:BrcB(10–43) mixture. Separate expression clones of BrcA and BrcB were constructed in E. coli, but these produced multiple fragments of the desired peptides with little or no activity. Various culture media (pep