No abstract

No abstract

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.

No abstract

The chemical structures of three new rnonobactams, PB-5266 A, B and C, were elucidated by their physico-chemical properties and spectrometric studies. In contrast to previously described monobactams, they all possess a dehydroasparagine residue.

concentrated below 30 °C to give the title compound, 0.79 g (70%).Cbz-Aep(OLi)-Gly(OLi) [18, (aa)i = Gly]. An ethanol solution (30 mL) of 11 [(aa)x = Gly, R = Me, 2.0 g, 5.6 mmol) was mixed with 2 N lithium hydroxide (17 mL). After 24 h at room temperature, the reaction mixture was neutralized with 1 N hydrochloric acid and concentrated below 30 °C. Upon mixing the residue with anhydrous ethanol, the title compound was precipitated as a powder, which was purified by reprecipitation using water and ethanol as dissolving and precipitating solvents, respectively, 1.96 g (52%).H-Gly-Aep(OLi)-Gly(OLi) (23). The tripeptide diester 16a (0.24 g, 0.58 mmol) was hydrogenated using Pd/C (10%, 0.12 g) in ethanol (10 mL) at atmospheric pressure and 25 °C for 1 h. After removal of the catalyst with suction filtration, the filtrate was mixed with 2 N lithium hydroxide (1.7 mL) and allowed to stand at room temperature for 20 h. The hydrolysate was then neutralized with 1 N hydrochloric acid and concentrated to afford the residue, which upon triturating with anhydrous ethanol gave amorphous powder, 0.11 g. The 1H NMR spectrum agreed with the assigned structure of the title compound, but also indicated