English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Sir: In the preceding papery, we reported that the differences in 13C NMR chemical shifts, 6, between C-4 and C-3, Jo(4-3), values of cephalosporins may be used as good reactivity indices for C-3 methylene substituent effects in both Nasalts and esters. It is well known that C-7 acylamino substituents have a great influence on antibacterial activities of cephalosporins2'. They are considered to have some effects on the reactivities of the compounds also, although it has been suggested that C-7 acylarnino substituents do not significantly affect the reactivity of the 13lactam ring3,4). As a result of an NMR study, PASCHAL et a1.5' described that the 5(C-8) and 5 (N-5) values are essentially insensitive to the variations in the 7-acylamino moiety. By detailed examinations of 7-acylamino substituent effects on the 13C NMR spectra of cephalosporins, we found that the 6(CONH) values correlate with the rate constants kou for the OH--catalyzed degradations''. We report our results here. The 13C spectral parameters of sodium cephalosporanates (Y-OCOCH3) and deacetoxycephalosporanates (Y =H) having a variety of 7,3acylamino substituents (XCONH) are listed in Table 1, which also includes data reported in the reference'). The 13C signals were assigned according to the methods reported previously-'). First, we plotted each 5(C-8) and X6(4-3) against d(CONH) observed for the deacetoxycephalosporanates (1-9) as shown in Fig. 1; similar plots for the cephalosporanates (10-20) are shown in Fig. 2. Although the 4o(4-3) and the 6(C-8) values changed only slightly with a change in the 7-acylamino substituents, each parameter exhibited a good linear relationship with the 6(CONH) value. In 11C NMR spectra of Nmethylamides, RCONHCH;,, a good linear relationship between the o(CONH) values and the inductive a, constants of R has been foundlo,11' In the cephalosporins examined here, a similar correlation between the 6(CONH) values and the al constants of X appears to exist at least partially (Fig. 3). This suggests that the o(C-8) values should also be correlated with the a, values of X. Compounds having 7-acylamino groups other than RCH,CONH, e.g., HCONH, CH,CONH, p-R-PhCONH, and Ft, appear not quite to fit into the correlations, which might be due to different molecular conformations including the 3cephem-ring geometry. The log ko$ values for the OH--catalyzed degradation of cephalosporins reported by YAMANA and Tsuji') were found to correlate better with the o(CONH) values of both cephalosporanate series

journal of antibiotics

NMR studies of penicillins and cephalosporins. IV. 7-Acylamino substituent effect on structure-reactivity relationship of cephalosporins studied by carbon-13 NMR spectroscopy.