Cephem Sulfones as Inactivators of Human Leukocyte Elastase. 5. 7.alpha.-Methoxy- and 7.alpha.-Chloro-1,1-dioxocephem 4-Ketones

Abstract

Studies on cephem sulfones as inhibitors of human leukocyte elastase (HLE) have been extended to the new class of cephem 4-ketones. tert-Butyl and phenyl ketones were prepared from 4-carboxycephem derivatives, at either the sulfide or sulfone oxidation level, by chemoselective Grignard reaction. Obtained products were functionalized with heterocyclothio and acyloxy substituents at C-3', C-2, or both positions. tert-Butyl ketones of the 7 alpha-chlorocephem series were in general at least as potent as the corresponding esters at inhibiting the enzyme, but improvements in hydrolytic stability were only marginal. On the other hand, tert-butyl ketones of the 7 alpha-methoxycephem series combined potent biochemical activity with acceptable hydrolytic stability, thus overstepping the esters, thiolesters, and amides reported previously. In particular, the tert-butyl ketones possessing a heterocyclothio group at C-3' or C-2 were at least as active as the corresponding tert-butyl esters but 1 order of magnitude more stable in physiologic buffers (pH 7.4, 37 degrees C). Introduction of acyloxy groups at C-2 delivered the most potent HLE inhibitors of the cephem class ever reported, with inhibition parameters often outside the determination limits of our standard protocol (second-order rate constant kon > 2,000,000 M-1 s-1; Ki at steady state < 2 nM). Keto-enol tautomerism was found to depress activity and boost hydrolytic stability. Thus, double substitution with heterocyclic thiols produced compounds with diverging properties, according to the extent of enolate formation at the investigated pH (7.4): the weakly acidic tert-butyl ketones (pKa > or = 5.8) proved to be potent inhibitors (kon over 10(4) M-1 s-1) with reasonable hydrolytic stability (t1/2 = 30-75 h), while the phenyl ketones (pKa < 4) were fair inhibitors (kon over 10(3) M-1 s-1; Ki at steady state approximately 50 nM) with hydrolytic half-lives exceeding 1000 h. Selected compounds efficiently inhibited the degradation of insoluble bovine neck elastin by HLE in a concentration-dependent manner. Intracellular HLE of polymorphonuclear leukocytes was in general unaffected; however, a lipophilic cephem sulfone apparently able to inactivate the enzyme in living cells was identified.

Synthesis, stability, biochemical and pharmacokinetic properties of a new potent and selective 4-oxo-β-lactam inhibitor of human leukocyte elastase

“…half-lives of 3 and 4 in PBS pH 7.4 are about 1 h) [31]. The half-life for the hydrolysis of 4-oxo-β-lactam 3 in human plasma is about 10 times lower than in PBS, indicating that 3 is very susceptible to hydrolysis catalysed by plasma enzymes, such as esterases.…”

Synthesis and cytotoxic properties of 7α-chloro-3-methyl-1,1-dioxoceph-3-ems, substituted with amide or keto group at position 4

“…Conversion of the 7α-chloro-3-methyl-1,1-dioxoceph-3-em-4-carbonyl chloride (3) into the 4-oxosubstituted cephems 8a-d using the Grignard reagents 7a-d was carried out by a published method [3]. In addition to the previously synthesized compounds 8b and 8c, the new cephems 8a and 8d with isopropylcarbonyl and 2-thienylcarbonyl substituents at position 4 were obtained (Scheme).…”

“…1 H NMR spectrum (90 MHz), δ, ppm (J, Hz): 1.98 (3H, s, 3-CH 3 ); 2.37 (3H, s, CH 3 at Py); 3.62 and 4.02 (2H, two d, AB system, 2 J = 18, SO 2 CH 2 ); 4.84 (1H, br. s, H-6); 5.37 (1H, d, 3 …”

“…Yield 46 mg (14%); mp 133°C (dec.). 1 H NMR spectrum (200 MHz), δ, ppm (J, Hz): 2.16 (3H, s, 3-CH 3 ); 3.02 and 3.07 (6H, two s, N(CH 3 ) 2 ); 3.51 and 3.97 (2H, two d, AB system, 2 J = 18, SO 2 CH 2 ); 4.87 (1H, d, 3 J = 1.6, H-6); 5.31 (1H, d,3 J = 1.6, H-7). Found, %: C 41.28, H 4.61, N 9.65.…”

“…1 H NMR spectrum, (90 MHz, CDCl 3 ), δ, ppm (J, Hz): 1.75 (3H, s, 3-CH 3 ); 3.31-4.00 (8H, m, 4CH 2 , morpholine); 3.80 and 4.00 (2H, two d, AB system, 2 J = 18, SO 2 CH 2 ); 4.88 (1H, br. s, H-6); 5.31 (1H, d, 3 Preparation of 4-Acyl-7α-chloro-3-methyl-1,1-dioxoceph-3-ems (8) (General Method). A mixture of oxalyl chloride (98 µl) and DMF (10µl) was added to a stirred suspension of the sulfone of a 7α-chloro-3-methylceph-3-em-4-carboxylic acid (300 mg, 1.13 mmol) in dichloromethane (20 ml) at room temperature.…”