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13C NMR spectra of cephalosporins. Signal assignments of free acids and esters

✍ Scribed by Kazuo Tori; Junko Nishikawa; Yoshito Takeuchi

Book ID
104241749
Publisher
Elsevier Science
Year
1981
Tongue
French
Weight
319 KB
Volume
22
Category
Article
ISSN
0040-4039

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✦ Synopsis

13C NMR signals were assigned for several cephalosporin free acids and esters as well as cephalosporinate ions using T1 measurements, selective NOE, and pDdependent chemical shifts to investigate the structure-reactivity relationship. Much interest has been shown in the chemistry of cephalosporins in relation to their useful biological activities in recent years. 2 13C and l5 N chemical shifts have been regarded as important indices in investigating the structure-activity relationship, and NMR signals were assigned for many cephalosporins, in particular, for cephalosporin sodium salts (a). 2-6 The polarization of the C-8 carbonyl group has frequently been discussed3 because the chemical reactivity of the B-lactam ring at the C-8-N-5 bond7 was shown to be closely correlated with the antibiotic activity.2'3 However, the chemical shifts (6) of C-8 and N-5 have been reported to be limited within a relatively narrow range. 3-6 Recently, Paschal et a1.4 suggested the importance of the C-3=C-4 double bond polarization to the activity in cephalosporinate ions (a), observing that the chemical shift differences between C-3 and C-4 [A6(4-3>] are large for cephalothin (2) and cephaloridine (9) which have been great commercial successes. The discrimination of the C-3 and C-4 signals had been a controversial problem, 5'8'g which was solved by measuring the dipole-dipole relaxation times (TI) in 3 in D20: 6 (TI) values are 118.8 (1.79 s) and 133.9 (5.13 s) for C-3 and C-4, respectively.5 We have also confirmed this result for cefazolin sodium salt (2) and @.

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