[Studies on oxacephems, an artificial type of beta-lactam antibiotics].

A pioneering work in the field of oxacephem antibiotics which had been carried out in our research laboratories is reviewed. Our research of beta-lactam antibiotics was started in 1974 with the policy to make chemical modification at the nuclei but not the side chain of the existing beta-lactam antibiotics, with an expectation to discover a new type of antibiotics. After the success in establishing an efficient synthetic method for 3'-norcephalosporin, we started oxacephem research in 1975. We succeeded in developing three synthetic methods starting from penicillins which efficiently served to prepare numerous oxacephem (1-oxa-1-dethia-cephalosporin) derivatives. It turned out that the oxacephem nucleus was much more distorted with an increased ring strain, resulting in reduction of the beta-lactam amide resonance to a greater extent than the cephalosporin nucleus. This physicochemical properties conferred an increased chemical reactivity on the nucleus as evidenced by an increased hydrolysis rate as compared with the corresponding 1-thia counterpart. This increased chemical reactivity coupled with the reduced hydrophobicity of the oxacephem nucleus as evidenced by the lower distribution constant in a water-octanol system, characterized unique biological properties of oxacephem derivatives. These include (1) 2-16 times increase in antibacterial activity with emphasis against gram-negative bacteria; (2) increased protecting effect in vivo parallel to the increased in vitro activity; (3) reduction of the stability to beta-lactamases leading to decreased antibacterial activity against the beta-lactamase producing strains; (4) 1.6-3.2 times increase in penetrability through the outer membrane of certain gram-negative bacteria, the increase being due to the increased hydrophilicity of the oxacephem nucleus; (5) remarkably reduced binding to human serum albumin improving the efficacy of the oxacephems in the blood; (6) a remarkable change in the excretion pattern, i.e. recovery in the bile reduced and that in the urine increased. These biological characteristics are generally favorable for antibacterial agents against pathogenic diseases except for the reduced stability to beta-lactamases. This unfavorable property of the oxacephem nucleus was the only barrier for developing a new agent of the oxacephem nucleus. However, this problem was relatively easily solved by introduction of (1) the methoxy group at 7 alpha and (2) appropriately alpha-substituted acyl amide chain at 7 beta; the former and the latter substituent effectively stabilized the oxacephems to various kinds of penicillinases and cephalosporinases, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Computer-aided molecular modeling of a thromboxane receptor antagonist S-145 and its related compounds.

Conformational analyses on thromboxane A2 (TxA2), its receptor agonist, U-46619, and its receptor antagonist, sulotroban, were carried out by molecular mechanics (MMFF) or molecular orbital (MNDO) methods. Two kinds of putative active conformations of TxA2 and the agonist were proposed on the basis of these results by referring to the hairpin conformation hypothesis. From the superposition of stable conformers of sulotroban on those conformers, the molecular structural requirements for potent TxA2 receptor antagonism were elucidated. S-145 in which these requirements are satisfied was a very potent TxA2 antagonist.

Synthesis and in vitro activity of stereoisomers of a novel thromboxane receptor antagonist, (+-)-(5Z)-7-[3-endo-[(phenylsulfonyl)amino]bicyclo [2.2.1]hept-2-exo-yl]heptenoic acid.

Three stereoisomers of S-145 (1) with variations at the side-chain junctions were synthesized. Endo-cis isomer 10 and N-exo-trans isomer 18 were obtained via the common intermediate 5 having an endo-fused ring structure. Exo-cis isomer 28 was prepared via exo-fused azetidino compound 21. Inhibitory concentrations (IC50) of the sodium salts newly obtained for platelet aggregation were measured using washed rat platelets (WP) and human platelet-rich plasma (PRP). The IC50 values of these compounds for contraction of the rat aorta were also measured. Compound 1 of N-endo-trans structure and N-exo-trans isomer 18 exhibited more potent inhibitory activity than cis-isomers 10 and 28 against responses induced by TXA2-related substances for rat WP and rat thoracic aorta. However, these compounds exhibited almost comparable inhibitory activity for human PRP.

An efficient, stereoselective synthesis of 4-E- and 4-Z-D-erythro-sphingenine and related compounds from 2-amino-2-deoxy-D-glucose.

Efficient, stereoselective synthesis of 4-E- and 4-Z-D-erythro-sphingenines having C16, C18, and C20 carbon-chains was achieved in 13 steps, starting from allyl 2-benzyloxycarbonylamino-2-deoxy-alpha-D-glucopyranoside. 2-Amino-1,6-di-O-tert- butyldiphenylsilyl-2-N,3-O-carbonyl-2-deoxy-D -allitol was used as the key intermediate.

Synthesis and in vitro activity of various derivatives of a novel thromboxane receptor antagonist, (+/-)-(5Z)-7-[3-endo-[(phenylsulfonyl)amino]bicyclo[2.2.1] hept-2-exo-yl]heptenoic acid.

Several sulfonyl derivatives (13a-t) of (+/-)-(5Z)-7-(3-endo-aminobicyclo[2.2.1]hept-2-exo-yl)heptenoic acid (VI) were synthesized via its methyl ester 10. Sulfonylation of 10 with 11a-t followed by saponification yielded 13a-t. Inhibitory concentrations (IC50) of the corresponding sodium salts 14a-t for platelet aggregation were measured with rat washed platelets (WP) and rabbit platelet-rich plasma (PRP). IC50 values of some derivatives for contraction of the rat aorta were also measured. The IC50 values for rat WP increased from 2.9 to 26 nM in the order of 14a, 14c, 14d, and 14b for derivatives with an arylsulfonyl residue, depending on the number of of intervening methylene groups. Methyl derivative 14e exhibited a higher IC50 value than n-hexyl derivative 14f. Substitution with a p-methyl, p-fluoro-, or p-chloro group in 14a retained or slightly reduced its IC50 value, while a p-n-pentyl or p-oxycarbonyl group augmented it significantly. The representative 14a suppressed (15S)-15-hydroxy-11,9-(epoxymethano)prosta-5(Z),13(E)-dienoic acid (U-46619) induced aggregation of human WP with an IC50 value of 7.7 nM, which corresponds well to the IC50 value of 3 nM obtained for each displacement by 14a of [3H]-U-46619 or (5Z,15 xi)-9 alpha, 11 alpha-(dimethylmethano)-15-hydroxy-16-(3-[125I]iodo- 4-hydroxyphenyl)-17,18,19,20-tetranor-13-aza-11a-carbathrombo-5-en oic acid [( 125I]-PTA-OH) bound to human WP. Synthesis of thromboxane A2 (TxA2) in human WP stimulated by thrombin was not inhibited by 14a at a concentration up to 10 microM. From these observations, the corresponding acid 13a (S-145) was concluded to be a potent TxA2 receptor antagonist.

Synthesis and 3'-substituent effects of some 7 alpha-methoxy-1-oxacephems on antibacterial activity and alkaline hydrolysis rates.

Relationships between intrinsic antibacterial activity and beta-lactam chemical reactivity of 7 beta-(phenylacetamido)-7 alpha-methoxy-1-oxacephems with various 3'-substituents were studied in order to clarify the effect of the 3'-substituent on the antibacterial activity. The chemical reactivity of the beta-lactam ring estimated by pseudo-first-order rate constants log kobsdNMR of alkaline hydrolysis at pD 10.4 and 35.0 degrees C correlates well linearly with 13C NMR chemical shift differences (delta delta(4-3], infrared stretching frequencies of the beta-lactam carbonyl (vC = O), and sigma I values. Values of log (1/CN), averaged for the MIC values for Escherichia coli, E. coli NIH JC-2, E. coli EC-14, and Klebsiella pneumoniae SRC-1, were taken as an estimation of the intrinsic antibacterial activity. The log (1/CN) values of the compounds without good leaving groups correlated fairly well with log kobsdNMR values. The comparatively high antibacterial activity of compounds with good leaving groups may be attributable to the different course of decomposition of these compounds.

1H NMR study of degradation mechanisms of oxacephem derivatives with various 3'-substituents in alkaline solution.

The degradation process of oxacephems with various 3'-substituents in alkaline solution was examined by 1H NMR spectroscopy, and the structures of two types of degradation products were determined: the hydrolysis products having the cleaved beta-lactam ring and the remaining 3'-substituents, and the exo-methylene compounds having the cleaved beta-lactam ring and the expelled 3'-substituents. The oxacephems were found to decompose, giving the former compounds that subsequently decomposed to the latter compound. Although the ratios of the formation of the exo-methylene compound 15 relative to the other degradation products depended on the leavability of the 3'-substituents, there was little correlation between the relative yields and the beta-lactam reactivity. Thus, the expulsion of the leaving group at the 3'-position was concluded to be not involved in the nucleophilic attack on the beta-lactam carbonyl.

Synthesis of several new carbapenem antibiotics.

A synthesis of several carbapenem antibiotics including 9-methoxythienamycin is described. The final deprotection of C-3 esters was accomplished by a novel procedure using aluminum trichloride under a very mild condition. The antibacterial activity against Gram-positive and Gram-negative bacteria is shown.

Synthesis and antibacterial activity of 6315-S, a new member of the oxacephem antibiotic.

The synthesis and in vitro activity of 7 beta-difluoromethylthioacetamido-7 alpha-methoxy-3-[[1-(hydroxyethyl)-1H- tetrazol-5-yl]thiomethyl]-1-oxa-3-cephem-4-carboxylic acid sodium salt, 6315-S, are described. 6315-S shows good antibacterial activity against Gram-positive and Gram-negative bacteria, being especially highly active against clinical isolates of Staphylococcus aureus resistant to either ampicillin or methicillin. The structure-activity relationship of related 1-oxa and 1-thia cephems is also presented.

Synthesis and substituent effects on antibacterial activity, alkaline hydrolysis rates, and infrared absorption frequencies of some cephem analogues related to latamoxef (moxalactam).

Relationships between intrinsic antibacterial activity and beta-lactam reactivity of 7 beta-[(4-hydroxyphenyl)acetyl]amino- and 7 beta-[(4-hydroxyphenyl)malonyl]amino derivatives of 1-oxa- and 1-thiacephems, with or without the 7 alpha-methoxy group (1-8), were investigated in order to clarify the enhanced antibacterial activity of latamoxef disodium (1). Substituent effects of a carbon atom at the 1- and 7 alpha-positions were also investigated by using racemic 1-carbacephem 9 and 7 alpha-methyl-1-oxacephem 10. Syntheses of 2-8 and 10 are also described. Acid chlorides derived from the O-benzyloxycarbonyl derivative of (4-hydroxyphenyl)acetic acid and the p-methoxybenzyl derivative of (4-hydroxyphenyl)malonic acid smoothly effected the introduction of these side chains. Conjugate addition of lithium dimethylcuprate to the quinoid system in 16 proceeded stereospecifically, furnishing the 7 alpha-methyl group for the synthesis of 10. Values of log (1/C) averaged for the sensitive Gram-negative strains (Escherichia coli NIHJ JC-2 and Klebsiella pneumoniae SRL-1) were taken as an estimation of the intrinsic antibacterial activity. The chemical reactivity of the beta-lactam ring was estimated either by pseudo-first-order rate constants (k) of alkaline hydrolysis measured at pH 9.20 and 35.0 degrees C or by infrared stretching frequencies of the beta-lactam carbonyl measured in dimethyl sulfoxide. Substitution of an oxygen atom at the 1-position increases both the hydrolysis rates and the antibacterial activity by a factor of approximately 6.3, while substitution of a 7 alpha-methoxy group increases the antibacterial activity by a factor of approximately 3.2 without significant change in the hydrolysis rates. The effect of the 7 alpha-methoxy group on the transition state in alkaline hydrolysis is discussed. Substitutions at the 1-position with a methylene group and, especially, at the 7 alpha-position with a methyl group greatly diminished the antibacterial activity, whereas the hydrolysis rate remained high with the substitution of a methylene group. Substitution of an oxygen atom for the sulfur atom at the 1-position of 1-thiacephems increased the beta-lactam carbonyl frequencies by approximately 6 cm-1, whereas introduction of a 7 alpha-methoxy group in 1-thia- and 1-oxacephems reduced the frequencies by approximately 5 cm-1.

Synthesis and antibacterial activity of 1-oxacephem derivatives.

A number of new optically active 1-oxacephem compounds were synthesized and tested for antibacterial activity. Various 7 alpha-unsubstituted 1-oxacephem nuclei 2a approximately 3 and a 7 alpha-methoxy-1-oxacephem nucleus 3, reported previously, were converted into the corresponding phenylacetylamino-, 2-thienylacetylamino-, D-mandelylamino-, D-phenylglycylamino-, and arylmalonylamino-1-oxacephem carboxylic acids. All the compounds except for the phenylglycylamine derivatives exhibited four-to sixteen-fold enhanced antibacterial activity compared with that of the corresponding cephalosporins. A combination of the 7 alpha-methoxy-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-1-oxacephem nucleus and a 7 beta-arylmalonylamino side chain, as represented by compound 1 (disodium salt of 33), produced the highest efficacy among them: high antibacterial activity with a widely expanded spectrum against Gram-negative bacteria including resistant strains and Pseudomonas aeruginosa was observed.