Synthesis of some new 2,3-disubstituted-4(3H)quinazolinone derivatives.

Quinazolinones are interesting materials because of their valuable biological effects. In this study some new 2,3-disubstituted-4(3H)quinqzolinone derivatives were synthesized from anthranilic acid in six steps by introducing a new chiral center to the aliphatic side chain of the quinazolinone. In the last step, a single acylation on the hydrazine moiety afforded final compounds. The structures of compounds were confirmed by IR, (1)HNMR and Mass spectra.

Antibacterial, antifungal and cytotoxic evaluation of some new quinazolinone derivatives.

Quinazolinone ring system is renown because of its wide spectrum of pharmacological activities due to various substitutions on this ring system. In this study, the minimum inhibitory concentration of the synthesized compounds in our laboratory was determined by micro dilution Alamar Blue(®) Assay against six strains of bacteria (three Gram-positive and three Gram-negative) and three strains of fungi. Following a broth micro dilution minimum inhibitory concentration (MIC) test, Minimum Bactericidal Concentration (MBC) and Minimum Fungicidal Concentration (MFC) tests were performed. Cytotoxic effects of the compounds were measured using the MTT colorimetric assay on HeLa cell line. Results of antimicrobial screening showed that compounds had better bacteriostatic activity against Gram-negative bacteria. Results from MBC revealed that these compounds had more significant bacteriostatic than bactericidal activities. Nearly all screened compounds showed good activity against C. albicans and A. niger. Results from MFC indicated that these compounds had better fungistatic rather than fungicidal activities. The synthesized target molecules were found to exhibit different cytotoxicity in the range of 10 to 100 µM on HeLa cell line. Compounds 6 and 7 exhibited acceptable cytotoxicity approximately 50% at 10 µM concentration.

Antibacterial, antifungal and cytotoxic evaluation of some new 2,3-disubstituted 4(3H)-quinazolinone derivatives.

In this study antibacterial, antifungal and cytotoxic effects of some new 2,3-disubstituted 4(3H)-quinazolinone derivatives have been evaluated. The in vitro antibacterial and antifungal tests of new synthesized compounds were performed using MABA method against six strains of bacteria (three Grampositive and three Gram-negative) and three strains of fungi. Also Minimum Bactericidal Concentration (MBC) and Minimum Fungicidal Concentration (MFC) tests were performed. All synthesized compounds indicated mild antibacterial effects especially against Gram-negative bacteria. The most sensitive bacteriumwas E. coli. All strains of tested fungi were sensitive to the synthesized compounds mostly at 32 µg/ml and there was no significant differences in the sensitivity of the tested compounds. MBC and MFC data indicated that tested compounds act as bactriostatic and fungistatic agents. Cytotoxic activity of the compounds was screened at 1, 10 and 100 µM concentrations against HeLa cells using the MTT colorimetric assay. While the synthesized compounds did not show significant cytotoxic activities, compounds 7a(3) and 7a(4) reduced cell viability to about 50% at 100 µM concentration. The present study revealed that most of the new synthesized compounds possess good antifungal effects and they could be considered as valuable candidates for further structural modification to design more potent antifungal agents.

Synthesis of some new tricyclic 4(3H)-quinazolinone derivatives.

Quinazolinones are interesting molecules with a wide range of biological activities. We prepared a number of quinazolinone derivatives by the condensation of 5-bromo- or 5-nitro-substituted anthranilic acids with chloro-acyl chlorides. Anthranilic acid derivatives were treated with either 3-chloro-propionyl chloride or 4-chloro-butyryl chloride to yield the corresponding N-acyl-anthranilic acids. The resultants were reacted with acetic anhydride to afford the benzoxazinone intermediates, which upon condensation with elected amines in either DMF or ethanol gave the corresponding tricyclic 4(3H)-quinazolinone derivatives. It was found that reactions in DMF produced higher yields.

Kinetic and conformational studies of adenosine deaminase upon interaction with oxazepam and lorazepam.

Oxazepam and lorazepam inhibit the adenosine deaminase (ADA) differently. In the case of lorazepam temperature increment causes an increase in the inhibition potency whereas higher temperature reduces the inhibitory effect of oxazepam; which proposes the overall profounder structural changes in the case of lorazepam relative to those caused by oxazepam.

The effects of deferiprone and deferasirox on the structure and function of beta-thalassemia hemoglobin.

Transfusional iron overload is a major cause of morbidity and mortality in thalassemia, sickle-cell disease and other chronic anemias. To overcome these problems, orally bio available iron chelators, deferiprone and deferasirox, were used for the treatment of patients suffering from thalassemia. The interactions between deferiprone and deferasirox with the carrier protein, beta-thalassemia hemoglobin (Hb), were investigated using fluorescence, circular dichroism (CD) and UV-visible measurements at physiological condition. Strong fluorescence quenching on interactions of the above drugs with beta-thalassemia Hb were observed. Fluorescence quenching data of thalassemia Hb in the presence of deferasirox have shown greater affinity of binding. The number of binding sites to Hb for deferasirox was found to be more relative to those of the deferiprone. The effects of these drugs on the oxygen affinity of the thalassemia Hb were studied by spectroscopic methods using sodium dithionite. Results indicated that deferiprone reduces oxygen affinity (increases oxygen releasing ability) of Hb, while in the presence of deferasirox, oxygen affinity of Hb has significantly increased by dose-dependent manner. As such, deferasirox exhibited opposite effect relative to deferiprone on the function of thalassemia Hb. In clinical dose of deferiprone, CD results showed that, the alpha-helical content of thalassemia Hb significantly increased. By use of the clinical dose of deferasirox, however, a decrease in alpha-helical content of protein was observed, which resulted in decreasing stability of thalassemia Hb. Our study showed that reduction in stability of thalassemia Hb in the presence of deferasirox induced higher conformational changes in protein.

Fibril formation of lysozyme upon interaction with sodium dodecyl sulfate at pH 9.2.

Fibril formation seems to be a general property of all proteins. Its occurrence in hen or human lysozyme depends on certain conditions, namely acidic pHs or the presence of some additives. This paper studies the interaction of lysozyme with sodium dodecyl sulfate (SDS) at pH 9.2, using UV-visible spectrophotometry, circular dichroism (CD) spectropolarimetry, electron microscopy (EM) and chemometry. Based on observations such as the strange increase in absorbance at 650nm (pH 9.2) and the presence of intermediates, it is assumed that lysozyme fibrils have been formed at pH 9.2 in the presence of SDS as an anionic surfactant. Thioflavin T emission fluorescence and an EM image confirmed this assumption. beta-cyclodextrin was then used as a turbidity inhibitor to establish its effect on the distribution of intermediates that participate in fibril formation.

Diminishing of aggregation for bovine liver catalase through acidic residues modification.

The tendency of proteins to aggregate is an important problem in biotechnology and the pharmaceutical industry. Because proteins in the aggregated state generally do not have the same biological activity as proteins in the native state. In order to prevent aggregation, it is essential to know the effective parameters in anti-aggregation mechanism. Using a chemical protein modification approach, UV-vis and fluorescence spectroscopies and circular dichroism spectropolarimetry, this study investigates the parameters involved in anti-aggregation mechanism of bovine liver catalase. Our findings clearly indicate that the modified bovine liver catalase provides better protection than the native enzyme against thermal aggregation. It seems that a decrease in hydrophobicity resulting in chemical modification plays an important role in preventing aggregation.

The correlation of RNase A enzymatic activity with the changes in the distance between Nepsilon2-His12 and N delta1-His119 upon addition of stabilizing and destabilizing salts.

The effect of stabilizing and destabilizing salts on the catalytic behavior of ribonuclease A (RNase A) was investigated at pH 7.5 and 25 degrees C, using spectrophotometric, viscometric and molecular dynamic methods. The changes in the distance between N(epsilon2) of His(12) and N(delta1) of His(119) at the catalytic center of RNase A upon the addition of sodium sulfate, sodium hydrogen sulfate and sodium thiocyanate were evaluated by molecular dynamic methods. The compactness and expansion in terms of Stokes radius of RNase A upon the addition of sulfate ions as kosmotropic salts, and thiocyanate ion as a chaotropic salt, were estimated by viscometric measurements. Enzyme activity was measured using cytidine 2', 3'-cyclic monophosphate as a substrate. The results from the measurements of distances between N(epsilon2) of His(12) and N(delta1) of His(119) and Stokes radius suggest (i) that the presence of sulfate ions decreases the distance between the catalytic His residues and increases the globular compactness, and (ii) that there is an expansion of the enzyme surface as well as elongation of the catalytic center in the presence of thiocyanate ion. These findings are in agreement with activity measurements.

Cooperative alpha-helix formation of beta-lactoglobulin induced by sodium n-alkyl sulfates.

It is generally assumed that folding intermediates contain partially formed native-like secondary structures. However, if we consider the fact that the conformational stability of the intermediate state is simpler than that of the native state, it would be expected that the secondary structures in a folding intermediate would not necessarily be similar to those of the native state. beta-Lactoglobulin is a predominantly beta-sheet protein, although it has a markedly high intrinsic preference for alpha-helical structure. The formation of non-native alpha-helical intermediate of beta-lactoglobulin was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS at special condition. The effect of n-alkyl sulfates on the structure of native beta-lactoglobulin at pH 2 was utilized to investigate the contribution of hydrophobic interactions to the stability of non-native alpha-helical intermediate. The addition of various concentrations of n-alkyl sulfates to the native state of beta-lactoglobulin (pH 2) appears to support the stabilized form of non-native alpha-helical intermediate at pH 2. The m values of the intermediate state of beta-lactoglobulin by SOS, SDeS, SDS and STS showed substantial variation. The enhancement of m values as the stability criterion of non-native alpha-helical intermediate state corresponded with increasing chain length of the cited n-alkyl sulfates. The present results suggest that the folding reaction of beta-lactoglobulin follows a non-hierarchical mechanism and hydrophobic interactions play important roles in stabilizing the non-native alpha-helical intermediate state.

A thermodynamic study on the interaction between magnesium ion and human growth hormone.

A thermodynamic study on the interaction between magnesium ion and human growth hormone (hGH) was studied at 27 degrees C in NaCl solution (50 mM) using different techniques. Two techniques of ionmetry using a Mg2+selective membrane electrode and isothermal titration calorimetry were applied to obtain the binding isotherm for hGHMg2+; results obtained by both techniques were found to be in good agreement. There is a set of three identical and noninteracting binding sites for magnesium ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 46 microM and -17.7 kJ/mol, respectively. Temperature scanning UV-visible spectroscopy was applied to elucidate the effect of Mg2+ binding on the protein stability, and circular dichroism (CD) spectroscopy was used to show the structural change of hGH due to the metal ion interaction. Magnesium ion binding increased the protein thermal stability by increasing the alpha-helix content as well as decreasing both beta and random coil structures. However, the secondary structural change of the protein returns to its native form, including a small change in the tertiary structure, in high concentrations of magnesium ion.

QSAR analysis for ADA upon interaction with a series of adenine derivatives as inhibitors.

The kinetic parameters of adenosine deaminase such as Km and Ki were determined in the absence and presence of adenine derivatives (R1-R24) in sodium phosphate buffer (50 mM; pH 7.5) solution at 27 degrees C. These kinetic parameters were used for QSAR analysis. As such, we found some theoretical descriptors to which the binding affinity of adenosine deaminase (ADA) towards several adenine nucleosides as inhibitors is correlated. QSAR analysis has revealed that binding affinity of the adenine nucleosides upon interaction with ADA depends on the molecular volume, dipole moment of the molecule, electric charge around the N1 atom, and the highest of positive charge for the related molecules.

Inhibition study of adenosine deaminase by caffeine using spectroscopy and isothermal titration calorimetry.

Kinetic and thermodynamic studies were made on the effect of caffeine on the activity of adenosine deaminase in 50 mM sodium phosphate buffer, pH 7.5, using UV spectrophotometry and isothermal titration calorimetry (ITC). An uncompetitive inhibition was observed for caffeine. A graphical fitting method was used for determination of binding constant and enthalpy of inhibitor binding by using isothermal titration microcalorimetry data. The dissociation-binding constant is equal to 350 microM by the microcalorimetry method, which agrees well with the value of 342 microM for the inhibition constant that was obtained from the spectroscopy method. Positive dependence of caffeine binding on temperature indicates a hydrophobic interaction.

Formation of the molten globule-like state of cytochrome c induced by n-alkyl sulfates at low concentrations.

The molten globule state of cytochrome c is the major intermediate of protein folding. Elucidation of the thermodynamic mechanism of conformational stability of the molten globule state would enhance our understanding of protein folding. The formation of the molten globule state of cytochrome c was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS, at low concentrations. The refolding states of the protein were monitored by spectroscopic techniques including circular dichroism (CD), visible absorbance and fluorescence. The effect of n-alkyl sulfates on the structure of acid-unfolded horse cytochrome c at pH 2 was utilized to investigate the contribution of hydrophobic interactions to the stability of the molten globule state. The addition of n-alkyl sulfates to the unfolded state of cytochrome c appears to support the stabilized form of the molten globule. The m-values of the refolded state of cytochrome c by SOS, SDeS, SDS, and STS showed substantial variation. The enhancement of m-values as the stability criterion of the molten globule state corresponded with increasing chain length of the cited n-alkyl sulfates. The compaction of the molten globule state induced by SDS, as a prototype for other n-alkyl sulfates, relative to the unfolded state of cytochrome c was confirmed by Stokes radius and thermal transition point (T(m)) measured by microviscometry and differential scanning calorimetry (DSC), respectively. Thus, hydrophobic interactions play an important role in stabilizing the molten globule state.

Thermodynamic analysis of human serum albumin interactions with glucose: insights into the diabetic range of glucose concentration.

The interaction of proteins with glucose results in their non-enzymatic glycation and influences their structural and functional properties. Human serum albumin (HSA) interacts with glucose forming glycated HSA. However, the glucose binding sites and the thermodynamic characteristics of the glycated HSA require further delineation. Here, the binding properties of HSA and glucose were studied utilizing fluorescent techniques. HSA was incubated with glucose in the 0-300mM range at 27 or 37 degrees C. The interaction of HSA with glucose showed two sets of binding sites. The first set consists of two sites with positive cooperativity and the second set consists of nine identical non-cooperative sites. The percentage of glycated HSA (gly%) and the moles of glucose bound to moles of HSA (r) were utilized to obtain binding constants and thermodynamic parameters based on the Wyman binding potential. The enthalpy of binding, obtained by van't Hoff relation, presented exothermicity up to 7mM glucose (126mg/dl, normal range) and endothermic propensity at higher glucose concentrations (>7mM, diabetic range). The start of endothermic propensity was consistent with the diabetic range of glucose concentration and indicates unfolding of HSA. The Gibbs free energy and entropy of binding further supports the unfolding of HSA. Therefore, glucose interacts with multiple sites on HSA affecting its biochemical and biophysical properties. This may interfere with HSA normal function contributing to diabetic complications.

Design, synthesis, and biological evaluation of novel nucleoside and nucleotide analogues as agents against DNA viruses and/or retroviruses.

A novel strategy was developed for the synthesis of N(7)-purine acyclic nucleosides 9 and 14. The key step involved the reaction between [2-(p-methoxyphenyloxy)ethoxy]methyl chloride and N(9)-tritylated nucleobases 6 or 11 followed by concomitant self-detritylation. N(7)-Guanine acyclic nucleoside 9 exhibited antiviral activity, but was phosphorylated by both HSV and Vero cell thymidine kinases. Thus, it showed more potent cellular toxicity than acyclovir (2). N(7)-Adenine acyclic nucleoside 14 was found to be an excellent antiviral agent as well as a good inhibitor of calf mucosal adenosine deaminase. This inhibitory property allows for a greater expression of antiviral activity of antiviral agents, such as N(9)-adenine acyclic nucleoside 1 and ara-A (3). Compound 14 was phosphorylated neither by herpes simplex virus (HSV) thymidine kinase nor by Vero cell thymidine kinase, yet it enhanced the rate constant for the monophosphorylation of acyclovir (2) by HSV thymidine kinase. Consequently, the combination of acyclovir (2) and 14 exhibited greater antiviral activity than acyclovir alone. 7-[2-(Phosphonomethoxy)ethyl]adenine (20) was also synthesized. The key step involved the reaction of 9-(2-cyanoethyl)adenine (15) with methyl iodoacetate in the presence of lithium 2,2,6,6-tetramethylpiperidine in THF. Unlike 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA, 4), the N(7)-isomer 20 was not phosphorylated effectively by 5-phosphoribosyl 1-pyrophosphate synthetase (PRPP synthetase). Thus, it did not exhibit pronounced antiviral activity. Dinucleotide 5'-monophosphate 24 and its butenolide ester 25 were also synthesized. Compound 24 showed substrate activity toward PRPP synthetase and exhibited notable activity against DNA viruses. The antiviral activity of the ester derivative 25 was found to be higher than that of the parent molecule 24. Dinucleotide 5'-monophosphate 24 is susceptible to degradation by snake venom and spleen phosphodiesterases. However, its respective butenolide ester derivative 25 was completely resistant to snake venom and spleen enzymes. Butenolide ester derivatives 28 and 29 were also synthesized and exhibited notable anti-DNA virus and anti-retrovirus activity in vitro. Compounds 2, 4, 9, 14, 20, 24, 25, and 28 were also evaluated for their inhibitory effect on HSV-1-induced mortality in NMRI mice. N(7)-adenine acyclic nucleoside 14 [LD(50) (intraperitoneal, ip) 950 mg/kg], nucleotide-containing butenolide 25 [LD(50) (ip) 675 mg/kg], and butenolide 28 [LD(50) (ip) 710 mg/kg] were found to be potent anti-HSV-1 agents in vivo. In addition, butenolide 28 efficiently decreased tumor formation induced by Moloney murine sarcoma virus (MSV) in NMRI mice while significantly increasing the survival time of MSV-infected mice.

Self-sensitized photooxygenation of 3,4-dialkoxyfurans to vitamin C or its derivatives.

Self-sensitized photooxygenation of 3,4-dialkoxyfurans 3a-d with molecular oxygen and UV- or sunlight at room temperature gave vitamin C derivatives 2a-d in good to excellent yields. Furan 3c, having photodegradable protecting groups, was also photooxygenated to give L-ascorbic acid (1) in a "one-pot" reaction. Furthermore, a novel photolytic transformation was developed for deuteration of furan 3b at the C-2 position with D(2)O to give furan 3d in 95% yield. Toxicity of furans 3a-c and butenolides 2a-c against human embryonic cell, murine embryo fibroblasts, normal fibroblasts, HeLa, and Vero cell lines in the presence of oxygen and indirect solar light was found to be much less than those of the antipsoriasis drugs anthralin and 8-methoxypsoralen.

Design and synthesis of a cephalosporin-retinoic acid prodrug activated by a monoclonal antibody-beta-lactamase conjugate.

Two novel series of all-trans-beta-retinoic acid derivatives were synthesized and found to possess anticancer activity. The first series, cephalosporin 3'-retinoic esters 6 and 7 were, respectively, obtained by the condensation of all-trans-beta-retinoic acid (2) with cephalosporins 4 and 5. The second series, 7-(retinamido)cephalosporins 11 and 12, were synthesized, respectively, by the condensation of 2 with cephalosporins 9 and 10. These four heretofore undescribed compounds 6, 7, 11, and 12 showed inhibitory activity against murine leukemias (L1210 and P388), sarcoma 180, breast carcinoma (MCF7), and human T-lymphocytes (Molt4/C8 and CEM/0). They also inhibited squamous metaplasia and keratinization in tracheal organ cultures derived from vitamin-A-deficient hamsters. Moreover, cephalosporin 3'-retinoic ester 7 exhibited enhanced activity against keratinization with ED(50)=3.91 x 10(-11) M in the presence of a beta-lactamase from Staphylococcus aureus 95. A tumor targeting fusion protein (dsFv3-beta-lactamase) was also used in conjunction with cephem-based retinoid 7 and the potency of 7 toward L1210, P388, and MCF7 was found to approach that of the free retinoic acid (2). In the presence of dsFv3-beta-lactamase, tumor cells were found to be much more susceptible to retinoid 7 than normal human embryonic lung cells. These notions provide a new approach to the use of beta-retinoic acid for antitumor therapy.

Synthesis and biological evaluation of purine-containing butenolides.

6-Chloropurine derivatives of gamma-(Z)-ethylidene-2,3-dimethoxybutenolide 3a, gamma-(Z)-ethylidene-2-methoxy-3-(4-nitro)benzyloxybutenolide 3b, gamma-(Z)-ethylidene-2-(4-nitro)benzyloxy-3-methoxybutenolide 3c, gamma-(Z)-ethylidene-2,3-di(4-nitro)benzyloxybutenolide 3d, and dimethylphosphono-gamma-(Z)-ethylidene-2,3-dimethoxybutenolide 11 as well as the adenine derivative of gamma-(Z)-ethylidene-2,3-dimethoxybutenolide 6 were synthesized. The key steps in the high-yield synthesis of 6 involved hydration/dehydration of the C(4)=C(5) in the precursor 3a. In the presence of NH4OH at elevated temperature, 3a underwent a reverse Michael-type addition with water to produce hydrate 5. At 37 degrees C, 6 was also hydrated in the presence of S-adenosyl-L-homocysteine hydrolase to afford 5. Butenolide 6 exhibited an inhibitory property toward the enzyme. Such type II (enzyme-mediated addition of water across C(4)=C(5)) mechanism is the first example of "enzyme-substrate intermediate" inactivation of S-adenosyl-L-homocysteine hydrolase. In contrast with type I mechanism-based inactivation, reduction of enzyme-bound NADP(+) to NADPH was not observed. Upon treatment with HCl, stereoselective dehydration of 5 occurred to give the target molecule 6. At ambident temperature, 3a was hydrated in the presence of NH4OH or pig liver esterase to produce 6-chloropurine derivative 4. An unambiguous proof of the structures of 3-5 was obtained by X-ray crystallographic analysis. For the synthesis of phosphonate derivative 11, the key step involved chlorination of phosphonate 9 by use of CF3SO2Cl and 1,8-diazabicyclo[5.4.0]undec-7-ene in CH2Cl2. 6-Chloropurine-containing butenolide 3d, 6-chloropurine derivative of 4-hydroxybutenolide 4, and adenine-containing 4-hydroxybutenolide 5 did not show anticancer and antiviral activities. 6-Chloropurine-containing ethylidene-2,3-dialkoxybutenolides 3a-c and phosphonate 11, however, exhibited inhibitory activity against murine leukemias (L1210 and P388), breast carcinoma (MCF7), and human T-lymphoblasts (Molt4/C8 and CEM/0) cell lines. They were also notably active toward thymidine kinase-deficient varicella-zoster virus (TK(-)VZV). Adenine-containing ethylidene-2,3-dimethoxybutenolide 6 exhibited marked selectivity in cytostatic activity against the murine leukemia (P388) cell line.

Design, synthesis, and SAR of novel carbapenem antibiotics with high stability to Xanthomonas maltophilia oxyiminocephalosporinase type II.

Racemic cis-6-(phenylacetamido)carbapenem (21), 2-hydroxycarbonyl-cis-6-(phenylacetamido)carbapenem (22), 2-methoxycarbonyl-cis-6-(phenylacetamido)carbapenem (30), 2-methoxycarbomethyl-cis-6-(phenylacetamido)carbapenem (33), 2-hydroxyethyl-cis-6-(phenylacetamido)carbapenem (34), and 2-acetoxyethyl-cis-6-(phenylacetamido)carbapenem (35) were synthesized. Formation of the carbapenem nuclei in 21, 22, and 30 involved dehydrophosphonation of the corresponding 2-diphenylphosphono-6-(phenylacetamido)carbapenam precursors 14, 15, and 28 using trimethylsilyl triflate and 1,8-diazabicyclo[5.4.0]undec-7-ene in THF. Syntheses of carbapenems 33-35 involved a Wittig reaction of carbapenam 14 with methyl glyoxylate in the presence of lithium 2,2,6,6-tetramethylpiperidine in THF. For the antibacterial activities against Staphylococcus aureus FDA 209P, S. aureus 95, Escherichia coli ATCC 39188, Klebsiellapneumoniae NCTC 418, Pseudomonas aeruginosa 1101-75, and P. aeruginosa 18S-H, carbapenems (+/-)-21, (+/-)-22, (+/-)-30, and (+/-)-33-35 were found comparable with imipenem ((+)-3), yet they were notably more potent than (+)-3 against Xanthomonas maltophilia GN 12873. On the other hand, unlike (+)-3, carbapenems (+/-)-21, (+/-)-22, (+/-)-30, and (+/-)-33-35 were stable to X. maltophilia oxyiminocephalosporinase type II. Their beta-lactamase inhibitory properties, however, were found to be more comparable with those of penicillin G ((+)-4) than to those of imipenem ((+)-3). A combination of imipenem ((+)-3) with (+/-)-21, (+/-)-22, (+/-)-30, and (+/-)-33-35 resulted in synergistic antibacterial activity against X. maltophilia GN 12873. Results from the biological tests were correlated with the distribution of the electron density at C(2)=C(3) of carbapenems upon reaction with transpeptidases or beta-lactamases.