A Simple Preparative Method fortert-Butyl Protection of Aminocephalosporanic Acid

Progress towards a stable cephalosporin-halogenated phenazine conjugate for antibacterial prodrug applications

Resistant bacteria successfully evade the action of conventional antibiotic therapies during infection, often leading to significant illness and death. Our lab has discovered halogenated phenazine (HP) analogues which demonstrate potent antibacterial activities through a unique iron-starving mechanism. Herein, we describe synthetic efforts towards a stable cephalosporin-HP conjugate prodrug with the aim of translating HPs into useful clinical agents. Cephalosporin-antibiotic conjugates offer multiple advantages for antibacterial design, including the release of active agents through the targeting of intracellular cephalosporinase following selective ring-opening of the beta-lactam warhead. During these studies, carbonate-linked cephalosporin-HP conjugate 16 was synthesized; however, we were unable to successfully remove the ester group required for cephalosporinase processing. Cephalosporin-HP 16 was then utilized as a probe to investigate the stability of the carbonate linker in antibacterial assays and, as predicted, this compound proved to be inactive against Staphylococcus aureus (MIC > 100 µM). The lack of 16's antibacterial activity can be attributed to the carbonate linker remaining intact throughout the MIC assay, thus not liberating the active HP moiety. These efforts have led to a more stable cephalosporin-HP conjugate joined through a carbonate linker compared to a highly unstable ether linked analogue we previously reported.

Stereoselective Preparation of a Cyclopentane-Based NK1 Receptor Antagonist Bearing an Unsymmetrically Substituted Sec−Sec Ether

A highly efficient synthesis of the potent and selective NK-1 receptor antagonist 1 is described. The key transformation involved the etherification reaction between cyclopentanol 12 and chiral imidate 30 which was catalyzed by HBF4 to initially give ether 14 as a 17:1 mixture of diastereomers and in 75% combined yield. The diastereoselectivity was upgraded to 109:1 by crystallization of the triethylamine solvate 44 which was isolated in 54% yield from 12. Mechanistic studies confirmed that the etherification reaction proceeds through an unprecedented S(N)2 reaction pathway under typical S(N)1 reaction conditions.

Relationships between structure, antibacterial activity, serum stability, pharmacokinetics and efficacy in 3-(heteroarylthio)cephems. Discovery of RWJ-333441 (MC-04,546)

SAR studies in a series of related 3-(heteroarylthio)cephems determined that a relatively high chemical reactivity of the beta-lactam ring, modulated by electronic effects of substituents at C-3 and C-7, is necessary to achieve high in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA). Such high reactivity results in lowered hydrolytic stability and concomitantly increases susceptibility to beta-lactam ring opening mediated by serum enzymes. Therefore, optimization of anti-MRSA activity versus stability toward serum-mediated degradation required a fine balance of substituent effects. Serum stability studies (measured as percentage of parent drug degraded after 60 min incubation) revealed up to 80-fold difference in degradation rate in a series of closely related (3-heteroarylthio)cephems. Of the compounds evaluated, RWJ-333441 (MC-04,546) possessed the best balance of serum stability (6% degradation after 60 min incubation) and in vitro activity versus MRSA (S. aureus COL MIC=1 microgram/mL). Accordingly, RWJ-333441 displayed excellent in vivo efficacy versus methicillin-susceptible Staphylococcus aureus (MSSA, ED(50)=0.39 mg/kg in mouse sepsis model with S. aureus Smith) and good pharmacokinetic properties in the rat (Cl(total)=0.39 L/h/kg).

Preparation of tert-Butyl 6-Aminopenicillanate and its 6-Oxo and 6-Diazo Derivatives

A 1:1 1,4-dioxane– tert-butyl acetate mixture and BF3 etherate were used for an effective 6-aminopenicillanic acid conversion into the tert-butyl ester (64 ± 3% yield) which could be easily transformed into tert-butyl 6-oxo- and 6-diazo-penicillanates.

Purification and Characterization of a Lovastatin Esterase from Clonostachys compactiuscula

An esterase from the fungus Clonostachys compactiuscula selectively hydrolyzes lovastatin, a clinically useful antihypercholesterolemic agent. Lovastatin or lovastatin-related compounds were required to induce the activity of the lovastatin 8(prm1)-((alpha)-methylbutyryloxy) esterase. The 46-kDa esterase was purified from mycelial extracts by centrifugation and a single anion-exchange chromatographic separation. Maximal lovastatin esterase activity was found at pH 9.0 to 9.6 and at 25 to 30(deg)C. The addition of 5 to 20% methanol resulted in greater lovastatin hydrolysis, while the addition of other solvents (ethanol, isopropanol, butanol, ethyl acetate, isopropyl acetate, or tetrahydrofuran) decreased hydrolysis. Lovastatin was selectively hydrolyzed even in the presence of an excess of simvastatin, another antihypercholesterolemic agent that is structurally very similar to lovastatin. This lovastatin 8(prm1)-((alpha)-methylbutyryloxy) esterase can be used to prepare a core intermediate for the generation of novel antihypercholesterolemic agents or to purify simvastatin prepared by C methylation of the 2(S)-methylbutyryloxy side chain of lovastatin.