Makoto Sunagawa

Stability of meropenem and effect of 1 beta-methyl substitution on its stability in the presence of renal dehydropeptidase I.

The stability of meropenem in the presence of renal dehydropeptidase I (DHP-I) varied extremely with the animal source of the enzyme. Meropenem, compared with imipenem, was rather easily hydrolyzed by DHP-Is from mice, rabbits, and monkeys, while it showed a higher resistance to guinea pig and beagle dog DHP-Is. In addition, meropenem was four times more resistant than imipenem to human DHP-I. The 1 beta-methyl substituent on carbapenems, i.e., meropenem and 1 beta-methyl imipenem, made them considerably more resistant to mouse and swine DHP-Is than the 1-unsubstituted derivatives are.

A novel and efficient synthesis of the key intermediate of 1β-methylcarbapenem antibiotics from (s)-methyl 3-hydroxy-2-methylpropionate

Abstract A highly efficient synthesis of the key intermediate 2 of 1β-methylcarbapenems was accomplished in 10 steps and 30% overall yield starting from commercially available ( S )-methyl 3-hydroxy-2-methylpropionate. The explored synthetic scheme features the addition reaction of diketene with a chiral imine as a key diastereoselective step.

In Vitro and In Vivo Activities of Novel 2-(Thiazol-2-ylthio)-1β-Methylcarbapenems with Potent Activities against Multiresistant Gram-Positive Bacteria

ABSTRACT SM-197436, SM-232721, and SM-232724 are new 1β-methylcarbapenems with a unique 4-substituted thiazol-2-ylthio moiety at the C-2 side chain. In agar dilution susceptibility testing these novel carbapenems were active against methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE) with a MIC90 of ≤4 μg/ml. Furthermore, SM-232724 showed strong bactericidal activity against MRSA, in contrast to linezolid, which was bacteriostatic up to four times the MIC. SM-232724 showed good therapeutic efficacy comparable to those of vancomycin and linezolid against systemic infections of MRSA in cyclophosphamide-treated mice. The MICs of SM-197436, SM-232721, and SM-232724 for streptococci, including penicillin-intermediate and penicillin-resistant Streptococcus pneumoniae strains, ranged from ≤0.063 to 0.5 μg/ml. These drugs were the most active β-lactams tested against Enterococcus faecium, and the MIC90 s for ampicillin-resistant E. faecium ranged between 8 and 16 μg/ml, which were slightly higher than the value for linezolid. However, time-kill assays revealed the superior bactericidal activity of SM-232724 compared to those of quinupristin-dalfopristin and linezolid against an E. faecium strain with a 4-log reduction in CFU at four times the MIC after 24 h of exposure to antibiotics. In addition, SM-232724 significantly reduced the numbers of bacteria in a murine abscess model with the E. faecium strain: its efficacy was superior to that of linezolid, although the MICs (2 μg/ml) of these two agents are the same. Among gram-negative bacteria, these three carbapenems were highly active against Haemophilus influenzae (including ampicillin-resistant strains), Moraxella catarrhalis, and Bacteroides fragilis, and showed antibacterial activity equivalent to that of imipenem for Escherichia coli, Klebsiella pneumoniae, and Proteus spp. Thus, these new carbapenems are promising candidates for agents to treat nosocomial bacterial infections by gram-positive and gram-negative bacteria, especially multiresistant gram-positive cocci, including MRSA and vancomycin-resistant enterococci.

Synthesis and biological properties of a new series of anti-MRSA β-lactams; 2-(thiazol-2-ylthio)carbapenems

A series of 1 beta-methylcarbapenems containing variously C-2 substituted thiazol-2-ylthio groups were synthesized, and their in vitro anti-MRSA activity was examined. Among them, 1 beta-methyl-2-(4-arylthiazol-2-ylthio)carbapenems exhibited superior anti-MRSA activity. Introduction of a cationic moiety in the C-2 side chain not only reduced the binding to HSA but also increased the stability against DHP-I, without affecting the anti-MRSA activity. It was also found that the distance between the cationic moiety and the carbapenem skeleton was related to the strength of HSA binding and the stability against DHP-I.

Highly stereocontrolled synthesis of the 1β-methylcarbapenem key intermediate by the reformatsky reaction of 3-(2-bromopropionyl)-2-oxazolidone derivatives with a 4-acetoxy-2-azetidinone

Abstract The key synthetic intermediate ( 4 ) of 1β-methylcarbapenems (1–3) was efficiently synthesized by employing highly stereocontrolled Reformatsky reaction (C 4 -alkylation) of 3-(2-bromopropionyl)-2-oxazolidone derivatives ( 6 ) with (3R,4R)-4-acetoxy-3-[(R)-1-(t-butyldimethylsilyloxy)ethylJ-2-azetidinone (5) in the presence of zinc dust followed by removal of 2-oxazolidone moieties. The best diastereoselectivity (β:α=95:5) could be realized by uses of sterically crowded achiral 2-oxazolidone derivatives such as 4,4-dimethyl-, 4,4,5,5-tetramethyl, and 4,4-dibutyl-5,5-pentamethylene-2-oxazolidone and higher reaction temperatures (refluxing tetrahydrofuran). The remarkable diastereoselectivities observed for the Reformatsky reactions could be explained by means of the weakly chelating transition state models.

Synthesis and biological properties of a new series of anti-MRSA β-lactams; 2-(thiazol-2′-ylthio)carbapenems

Abstract Synthesis and biological properties of a new series of 1β-methyl carbapenems that have been variously substituted thiazol-2′-ylthio side chain on C-2 are described. Amongst synthesized compounds, 4′-arylthiazole derivatives showed potent anti-MRSA activity and the introduction of a quaternary cation was effective to reduce binding to human serum albumin without affecting the anti-MRSA activity.

The Mode of Action of 2-(Thiazol-2-ylthio)-1β-methylcarbapenems against Pseudomonas aeruginosa : The Impact of Outer Membrane Permeability and the Contribution of MexAB-OprM Efflux System

The mode of action of a series of 2-(4-dihydropyrrolylthiazol-2-ylthio) and 2-(4-tetrahydropyridinylthiazol-2-ylthio)-1β-methylcarbapenem analogues against Pseudomonas aeruginosa was investigated with regard to contributions of the affinity for penicillin binding proteins (PBPs), the outer membrane permeability, and the effect of the MexAB-OprM efflux system. In this series of carbapenems, the introduction of a substituent in C-2 side chain with a change in physicochemical properties affected the antipseudomonal activity depending on the molecular weight. However, these structural modifications did not affect the affinity for pseudomonal PBPs significantly. It was confirmed that the affinity for PBPs was not an important determinant of the antipseudomonal activity of this series of carbapenems. OprD porin-deficiency did not affect antipseudomonal activity either. On the other hand, the MIC of these carbapenems against P. aeruginosa significantly decreased in the presence of outer membrane permeabilizer. This result strongly suggests that the cause of the relatively low antipseudomonal activity of these carbapanems is their low permeability through the outer membrane of P. aeruginosa. And also, in the presence of outer membrane permeabilizer, the MICs against MexAB-OprM deficient mutants remarkably decreased and were very close to the value of the IC50 for pseudomonal PBPs. From this result, it was clear that the effect of the MexAB-OprM efflux system was also an important determinant of antipseudomonal activity of these carbapenems. In conclusion, the major determinants of the antipseudomonal activity of the 2-(thiazol-2-ylthio)-1β-methylcarbapenems are the outer membrane permeability and the effect of the MexAB-OprM efflux system, not the affinity for pseudomonal PBPs.

Conformational analysis of meropenem and desmethyl meropenem: the effect of 1β-methyl group on carbapenem antibiotics☆

Abstract The conformations of meropenem and desmethyl meropenem have been studied using MM calculations and 1H NMR experiments. It was found that the preferred conformation of meropenem was relatively linear compared with desmethyl meropenem in aqueous solution.

Structural comparison of 1 β -Methylcarbapenem, Carbapenem and Penem: NMR studies and theoretical calculations

Structural comparisons of meropenem (1), desmethyl meropenem (2) and the penem analogue (3) which contain the same side chains at both C-2 and C-6 were performed using 1H NMR measurements together with 3-21G* level of ab initio MO and molecular mechanics calculations. The ab initio MO calculations reproduced the skeletons of these strained beta-lactam rings in good agreement with the crystallographic data. 1H NMR measurements in aqueous solution together with molecular modeling studies indicated that there were conformational differences of the C-2 and C-6 side chains in this series of compounds. These observations suggested that the conformational differences could affect their biological activities.

STRUCTURAL ANALYSIS BY NMR OF ANTITUMOR DRUG-DNA COMPLEXES : 9-AMINOANTHRACYCLINE (SM-5887)

Abstract SM-5887 is an anthracycline antibiotic with a potent antitumor activity and low toxicity. The structure of the 2:1 SM-5887 -d(CGTACG) complex has been studied in solution by 2D NMR spectroscopy. These data revealed that SM-5887 intercalated between the cytosine and guanine residues and the sugar moiety lay in the minor groove. The intercalation geometry of SM-5887 was a hybrid between those of adriamycin and nogalamycin.