The structure of furanomycin has been established from the X-ray crystal structure analysis of its N-acetyl-derivative, to be (+)-(as, 5S, 2R)-a-amino (2,5dihydro-&methyl) f uran-2-acetic acid.
Structures of interesting acylpeptide antibiotics cepafungins I, II and III were elucidated by NMR spectroscopic studies and some degradation experiments. The antibiotics contain a common peptide part that consists of threonine and two unusual amino acid residues, y-hydroxylysine and 4-amino-2-pentcnoic acid. The unusual amino acid residues compose an interesting 12-membered ring with an exocyclic JV-terminus to which the threonine is connected. Different fatty acyl groups connected to the TV-terminus of the threonine distinguish the three cepafungins. The major component I and minor component III are new substance, but the minor component II has a structure identical with that of the recently reported antibiotic glidobactin A.The present report describes the structure elucidation of cepafungins I, II and III produced by Pseudomonas sp. CB-31}.On the Major Component Cepafungin I Elemental analysis and SI-MS showed the molecular formula ofcepafungin 1(1) to be C28H46N4O6. The *H NMRanalysis in DMSO-d6, including temperature variation, D2O addition, homonuclear chemical shift correlation (HOMCOR)2), and decoupling experiments confirmed the 46 protons of 1 (40 nonexchangeable, 4 amide and 2 hydroxy protons). The 13C NMRanalysis, including single frequency Fig. 1. One-bond C-H HETCOR spectrum of 1 in DMSO-^6 at 25°C.
Relationships between the chemical reactivity of 3-substituted cephalosporins or 3-methylene-substituted cephalosporins and several parameters observed by 13C NMR and IR spectroscopies are described. Among 3-substituted cephalosporins, the values of delta (C-3) and delta (COO) of 13C NMR spectra are correlated with the logarithms of the rate constants for alkaline hydrolysis (log kobsd) when substituents at the 3-position are classified into two groups, i.e., OR substituents and others. Among the 3-methylene-substituted cephalosporins, the difference values of the 13C chemical shifts for C-3 and C-4, delta delta (4-3), are correlated with log kobsd. The beta-lactam vC = O value of the solution IR spectra is a good index for the prediction of a significant change of the beta-lactam reactivity resulting from modification of a 3-substituent or a 3-methylene substituent. From analysis of these observed parameters, both resonance and inductive effects of the substituent at the 3-position were found to affect the chemical reactivity of the beta-lactam ring in cephalosporin, while only the inductive effect of the substituent at the 3'-position was found to affect the beta-lactam reactivity.
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