Synthesis and antimycobacterial activities of ring-substituted quinolinecarboxylic acid/ester analogues. Part 1

Structural optimization of recently discovered new chemical entity, 2,8-dicyclopentyl-4-methylquinoline (DCMQ; MIC= 6.25 microg/mL, M. tuberculosis H37Rv) resulted in the synthesis of four new series of ring-substituted quinolinecarboxylic acids/esters constituting 45 analogues. All new derivatives were evaluated for in vitro antimycobacterial activities against M. tuberculosis H37Rv. Certain ring-substituted-2-quinolinecarboxylic acid ester and ring-substituted-2-quinoline acetic acid ester analogues described herein showed moderate to good inhibitory activity. In particular, three analogues methyl 4,5-dicyclopentyl-2-quinolinecarboxylate (3b), methyl 4,8-dicyclopentyl-2-quinolinecarboxylate (3c) and ethyl 2-(2,8-dicyclopentyl-4-quinolyl)acetate (14g) exhibited excellent MIC values of 1.00, 2.00 and 4.00microg/mL, respectively. Results obtained indicate that substitution of the quinoline ring with dicyclopentyl substituent presumably enhances the antimycobacterial activities in the quinoline analogues described herein.     

Conformationally restricted analogs of deoxynegamycin

Deoxynegamycin (1b) is a protein synthesis inhibitor with activity against Gram-negative (GN) bacteria. A series of conformationally restricted analogs were synthesized to probe its bioactive conformation. Indeed, some of the constrained analogs were found to be equal or better than deoxynegamycin in protein synthesis assay (1b, IC(50)=8.2 microM; 44, IC(50)=6.6 microM; 35e(2), IC(50)=1 microM). However, deoxynegamycin had the best in vitro whole cell antibacterial activity (Escherichia coli, MIC=4-16 microg/mL; Klebsiella pneumoniae, MIC=8 microg/mL) suggesting that other factors such as permeation may also be contributing to the overall whole cell activity. A new finding is that deoxynegamycin is efficacious in an E. coli murine septicemia model (ED(50)=4.8 mg/kg), providing further evidence of the favorable in vivo properties of this class of molecules.     

Antibacterial activity of triterpene acids and semi-synthetic derivatives against oral pathogens

Triterpene acids (ursolic, oleanoic, gypsogenic, and sumaresinolic acids) isolated from Miconia species, along with a mixture of ursolic and oleanolic acids and a mixture of maslinic and 2-a-hydroxyursolic acids, as well as ursolic acid derivatives were evaluated against the following microorganisms: Streptococcus mutans, Streptococcus mitis, Streptococcus sanguinis, Streptococcus salivarius, Streptococcus sobrinus, and Enterococcus faecalis, which are potentially responsible for the formation of dental caries in humans. The microdilution method was used for the determination of the minimum inhibitory concentration (MIC) during the evaluation of the antibacterial activity. All the isolated compounds, mixtures, and semi-synthetic derivatives displayed activity against all the tested bacteria, showing that they are promising antiplaque and anticaries agents. Ursolic and oleanolic acids displayed the most intense antibacterial effect, with MIC values ranging from 30 microg/mL to 80 microg/mL. The MIC values of ursolic acid derivatives, as well as those obtained for the mixture of ursolic and oleanolic acids showed that these compounds do not have higher antibacterial activity when compared with the activity observed with either ursolic acid or oleanolic acid alone. With regard to the structure-activity relationship of triterpene acids and derivatives, it is suggested that both hydroxy and carboxy groups present in the triterpenes are important for their antibacterial activity against oral pathogens.     

Isolation, structure, and antibacterial activity of thiazomycin A, a potent thiazolyl peptide antibiotic from Amycolatopsis fastidiosa

Thiazolyl peptides are a class of thiazole-rich macrocyclic potent antibacterial agents. Recently, we described thiazomycin, a new member of thiazolyl peptides, discovered by a thiazolyl peptide specific chemical screening. This method also allowed for the discovery of a new thiazolyl peptide, thiazomycin A, which carries modification in the oxazolidine ring of the amino sugar moiety. Thiazomycin A is a specific inhibitor of protein synthesis (IC(50) 0.7 microg/mL) and a potent Gram-positive antibacterial agent with minimum inhibitory concentration (MIC) ranging 0.002-0.25 microg/mL. The isolation and structure elucidation and biological activities of thiazomycin A are described.     

Design and synthesis of benzenesulfonanilides active against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus

Vancomycin is mainly used as an antibacterial agent of last resort, but recently vancomycin-resistant bacterial strains have been emerging. Although new antimicrobials have been developed in order to overcome drug-resistant bacteria, many are structurally complex beta-lactams or quinolones. In this study, we aimed to create new anti-drug-resistance antibacterials which can be synthesized in a few steps from inexpensive starting materials. Since sulfa drugs function as p-aminobenzoic acid mimics and inhibit dihydropteroate synthase (DHPS) in the folate pathway, we hypothesized that sulfa derivatives would act as folate metabolite-mimics and inhibit bacterial folate metabolism. Screening of our sulfonanilide libraries, including benzenesulfonanilide-type cyclooxygenase-1-selective inhibitors, led us to discover benzenesulfonanilides with potent anti-methicillin-resistant Staphylococcus aureus (MRSA)/vancomycin-resistant Enterococcus (VRE) activity, that is, N-3,5-bis(trifluoromethyl)phenyl-3,5-dichlorobenzenesulfonanilide (16b) [MIC=0.5microg/mL (MRSA), 1.0microg/mL (VRE)], and 3,5-bis(trifluoromethyl)-N-(3,5-dichlorophenyl)benzenesulfonanilide (16c) [MIC=0.5microg/mL (MRSA), 1.0microg/mL (VRE)]. These compounds are more active than vancomycin [MIC=2.0microg/mL (MRSA), 125microg/mL (VRE)], but do not possess an amino group, which is essential for DHPS inhibition by sulfa drugs. These results suggested that the mechanism of antibacterial action of compounds 16b and 16c is different from that of sulfa drugs. We also confirmed the activity of these compounds against clinical isolates of Gram-positive bacteria.     

Identification of a novel agonist of peroxisome proliferator-activated receptors alpha and gamma that may contribute to the anti-diabetic activity of guggulipid in Lep(ob)/Lep(ob) mice

The ethyl acetate extract of the gum of the guggul tree, Commiphora mukul (guggulipid), is marketed for the treatment of dyslipidaemia and obesity. We have found that it protects Lep(ob)/Lep(ob) mice from diabetes and have investigated possible molecular mechanisms for its metabolic effects, in particular those due to a newly identified component, commipheric acid. Both guggulipid (EC(50)=0.82 microg/ml) and commipheric acid (EC(50)=0.26 microg/ml) activated human peroxisome proliferator-activated receptor alpha (PPARalpha) in COS-7 cells transiently transfected with the receptor and a reporter gene construct. Similarly, both guggulipid (EC(50)=2.3 microg/ml) and commipheric acid (EC(50)=0.3 microg/ml) activated PPARgamma and both promoted the differentiation of 3T3 L1 preadipocytes to adipocytes. Guggulipid (EC(50)=0.66 microg/ml), but not commipheric acid, activated liver X receptor alpha (LXRalpha). E- and Z-guggulsterones, which are largely responsible for guggulipid's hypocholesterolaemic effect, had no effects in these assays. Guggulipid (20 g/kg diet) improved glucose tolerance in female Lep(ob)/Lep(ob) mice. Pure commipheric acid, given orally (960 mg/kg body weight, once daily), increased liver weight but did not affect body weight or glucose tolerance. However, the ethyl ester of commipheric acid (150 mg/kg, twice daily) lowered fasting blood glucose and plasma insulin, and plasma triglycerides without affecting food intake or body weight. These results raise the possibility that guggulipid has anti-diabetic activity due partly to commipheric acid's PPARalpha/gamma agonism, but the systemic bioavailability of orally dosed, pure commipheric acid appears poor. Another component may contribute to guggulipid's anti-diabetic and hypocholesterolaemic activity by stimulating LXRalpha.     

Sophorolipid production from different lipid precursors observed with LC-MS

An HPLC-MSⁿ system was used to quantify and identify the structures of individual sophorolipid components produced in Torulopsis bombicola fermentation on glucose with or without hexadecane or soybean oil. With glucose alone, the SL production was minimal and the products were complex mixtures with mainly acidic SLs. The SLs produced with glucose plus soybean oil were also complex, containing both lactonic and acidic SLs with saturated and unsaturated C16 and C18 fatty acid moieties. The glucose plus hexadecane system gave the highest production rate and product selectivity, forming primarily two diacetylated lactonic isomers with palmitate as the fatty acid moiety. A close structure correspondence between the SL’s lipid moiety and the lipid precursor used was observed. The change of the composition of SL mixtures along batch fermentation was further examined. The concentrations of acidic SLs increased very gradually throughout the process. The production of lactonic SLs became appreciable following the addition of hexadecane or soybean oil at 24 h, and increased much more rapidly after the culture reached the stationary phase. The combined percentage of the main lactonic SLs leveled off at 80% for the hexadecane system and 50% for the soybean oil system. The yields of crude SLs were 0.84, 0.20, and 0.03 g per gram of hexadecane, soybean oil, and glucose consumed during the SL production phase. Hexadecane is thus a more efficient second C-source for sophorolipid production.     

Synthesis, absolute stereochemistry and molecular design of the new antifungal and antibacterial antibiotic produced by Streptomyces sp.201

The absolute stereochemistry of the new antifungal and antibacterial antibiotic produced by Streptomyces sp.201 has been established by achieving the total synthesis of the product. A series of analogues have also been synthesized by changing the side chain and their bioactivity assessed against different microbial strains. Among them, 1e (R = C8H17) was found to be the most potent with MIC of 8 microg/mL against Mycobacterium tuberculosis, 12 microg/mL against Escherichia coli and 16 microg/mL against Bacillus subtilis 6 microg/mL against Proteus vulgaris. This was followed by 1b (R = C5H11) with MIC of 10-20 microg/mL range and 1d (R = C7H15) with MIC of 14-24 g/mL, whereas 1a (R = C4H9) and 1f (R = C18H35) were found to be completely inactive. Besides, 1c (R = C6H13) showed certain extent of antibacterial activity in the range of 24-50 microg/mL. Mycobacterium tuberculosis was very sensitive to 1e (R = C8H17) with MIC of 8 microg/mL. Antifungal activity of analogues 1d (R = C7H15) and 1e, (R = C8H17) against Fusarium oxysporum and Rhizoctonia solani were found promising with MFCs in the 15-18 microg/mL range.     

Two novel antibiotics, Sch 419558 and Sch 419559, produced by Pseudomonas fluorescens: effect on activity by overexpression of RpoE

Two new secondary metabolites designated as Sch 419558 (1) and Sch 419559 (2), were isolated from the fermentation broth of Pseudomonas fluorescens. Structure elucidation of 1 and 2 was accomplished by spectroscopic data analyses including MS and NMR experiments. Both compounds were identified as lipopeptides containing valine and threonine linked with 1-amino-1-hydroxy-heptadec-9-en-2-one or 1-amino-1-hydroxy-pentadecan-2-one carbon chains, respectively. Characterization of the amino acids was further confirmed by amino acid analysis. Compounds 1 and 2 exhibited antibacterial activity against a sensitized E. coli strain with minimum inhibitory concentration of 0.3 and 0.6 microg/mL, respectively. Overexpression of RpoE in the E. coli strain increased the MIC over 60-fold for compounds 1 and 2.     

Synthesis and potent antimicrobial activity of some novel methyl or ethyl 1H-benzimidazole-5-carboxylates derivatives carrying amide or amidine groups

A series of benzimidazole-5-carboxylic acid alkyl ester derivatives carrying amide or amidine substituted methyl or phenyl groups at the position C-2 were synthesised and evaluated for antibacterial and antifungal activities against S. aureus, methicillin resistant S. aureus (MRSA), S. faecalis, methicillin resistant S. epidermidis (MRSE), E. coli and C. albicans. The results showed that while all simple acetamides are essentially inactive, aromatic amides and amidines have potent antibacterial activities. Aromatic amidine derivatives 13 f-h exhibited the best inhibitory activity with 1.56-0.39 microg/mL MIC values against MRSA and MRSE.     

Antimycobacterial activities of 5-alkyl (or halo)-3'-substituted pyrimidine nucleoside analogs

Several 5-alkyl (or halo)-3'-azido (amino or halo) analogs of pyrimidine nucleosides have been synthesized and evaluated against Mycobacterium bovis, Mycobacterium tuberculosis and Mycobacterium avium. Among these compounds, 3'-azido-5-ethyl-2',3'-dideoxyuridine (3) was found to have significant antimycobacterial activities against M. bovis (MIC(50)=1μg/mL), M. tuberculosis (MIC(50)=10μg/mL) and M. avium (MIC(50)=10μg/mL).     

Molecular properties and antibacterial activity of the methyl and ethyl ester derivatives of ampicillin

Ampicillin is a beta-lactam antibiotic that is effective against gram-negative bacteria. Ampicillin has a single carboxyl group (-C(O)OH) within its structure which is suitable for forming ester compounds. Diazomethane and diazoethane were utilized to react with ampicillin to form the methyl and ethyl esters, respectively. The ester derivatives of ampicillin were solubilized together (mole ratio 1:1) in LB media and penicillin resistant Escherichia coli added to measure antibacterial activity. Growth inhibition of bacteria was monitored by optical density after a known time period and with known specific concentrations of the ampicillin esters present. Significant growth inhibition of penicillin resistant bacteria occurred at concentrations of the combined methyl and ethyl ampicillin esters from less than 50 microgram/mL to more than 150 microgram/mL. Molecular properties of the ester compounds were determined. The two ester derivatives showed values of Log BB, Log P, polar surface area, intestinal absorption, and solubility suitable for clinical application. The two ester compounds showed zero violations of the Rule of 5 indicating good bioavailability. The two ester derivatives showed greater intestinal absorbance and greater penetration of the blood brain barrier than the parent ampicillin. Favorable druglikeness was determined for both ester derivatives.     

Synthesis and antituberculosis activity of the derivatives of glycoside steviolbioside from the plant Stevia rebaudiana and diterpenoid isosteviol containing hydrazone, hydrazide and pyridinoyl moieties

Conjugates of antitubercular drug Isoniazid (hydrazide of isonicotinic acid), nicotinic and alpha-picolinic acid hydrazides and glycoside steviolbioside from the plant Stevia rebaudiana as well as the product of its acid hydrolysis, diterpenoid isosteviol, were synthesized. Besides, isosteviol hydrazide and hydrazone derivatives as well as conjugates containing two isosteviol moieties connected by dihydrazide linker were also obtained. Both initial compounds and their synthetic derivatives inhibit the growth of Mycobacterium tuberculosis (H37Rv in vitro). The minimum concentration at which the growth of M. tuberculosis was inhibited by 100% (MIC) for stevioside and steviolbioside equals 7.5 and 3.8 microg/mL, respectively. MIC values for conjugates of the hydrazides of pyridine carbonic acids and steviolbioside as well as isosteviol are in the ranges 5-10 and 10-20 microg/mL, respectively. Maximum inhibitory effect against M. tuberculosis showed the conjugates of isosteviol and adipic acid dihydrazide (MIC values ranged from 1.7 to 3.1 microg/mL). Antitubercular activity of the compounds studied is higher than the activity of antitubercular drug Pyrizanamide (MIC = 12.5-20 microg/mL) but lower than the activity of antitubercular drug Isoniazid (MIC = 0.02-0.04 microg/mL).     

The Use of Fatty Acid Esters to Enhance Free Acid Sophorolipid Synthesis

Fatty acid esters were prepared by transesterification of soy oil with methanol (methyl-soyate, Me-Soy), ethanol (ethyl-soyate, Et-Soy) and propanol (propyl-soyate, Pro-Soy) and used with glycerol as fermentation substrates to enhance production of free-acid sophorolipids (SLs). Fed-batch fermentations of Candida bombicola resulted in SL yields of 46 ± 4 g/l, 42 ± 7 g/l and 18 ± 6 g/l from Me-Soy, Et-Soy, and Pro-Soy, respectively. Liquid chromatography with atmospheric pressure ionization mass spectrometry (LC/API-MS) showed that Me-Soy resulted in 71% open-chain SLs with 59% of those molecules remaining esterified at the carboxyl end of the fatty acids. Et-Soy and Pro-Soy resulted in 43% and 80% open-chain free-acid SLs, respectively (containing linoleic acid and oleic acid as the principal fatty acid species linked to the sophorose sugar at the omega-1 position), with no evidence of residual esterification. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Carboxylic acid and phosphate ester derivatives of fluconazole: synthesis and antifungal activities

Two classes of fluconazole derivatives, (a) carboxylic acid esters and (b) fatty alcohol and carbohydrate phosphate esters, were synthesized and evaluated in vitro against Cryptococcus neoformans, Candida albicans, and Aspergillus niger. All carboxylic acid ester derivatives of fluconazole (1a-l), such as O-2-bromooctanoylfluconazole (1g, MIC=111 microg/mL) and O-11-bromoundecanoylfluconazole (1j, MIC=198 microg/mL), exhibited higher antifungal activity than fluconazole (MIC > or = 4444 microg/mL) against C. albicans ATCC 14053 in SDB medium. Several fatty alcohol phosphate triester derivatives of fluconazole, such as 2a, 2b, 2f, 2g, and 2h, exhibited enhanced antifungal activities against C. albicans and/or A. niger compared to fluconazole in SDB medium. For example, 2-cyanoethyl-omega-undecylenyl fluconazole phosphate (2b) with MIC value of 122 microg/mL had at least 36 times greater antifungal activity than fluconazole against C. albicans in SDB medium. Methyl-undecanyl fluconazole phosphate (2f) with a MIC value of 190 microg/mL was at least 3-fold more potent than fluconazole against A. niger ATCC 16404. All compounds had higher estimated lipophilicity and dermal permeability than those for fluconazole. These results demonstrate the potential of these antifungal agents for further development as sustained-release topical antifungal chemotherapeutic agents.     

3-[Benzimidazo- and 3-[benzothiadiazoleimidazo-(1,2-c)quinazolin-5-yl]-2H-chromene-2-ones as potent antimicrobial agents

A series of 3-[benzimidazo(1,2-c)quinazolin-5-yl]-2H-chromene-2-one (6a-6f) and 3-[benzothiadiazole- imidazo(1,2-c)quinazolin-5-yl]-2H-chromene-2-one derivatives (7a-7f) that incorporate a variety of substituents at the 6- and/or 8-positions of the coumarin moieties have been synthesized utilizing cellulose sulfuric acid as an efficient catalyst under both conventional heating and microwave irradiation procedures. These analogs were evaluated for their antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Streptococcus pyogenes (Gram-positive bacteria), Escherichia Coli, Klebsiella pneumonia, Salmonella typhimurium (Gram-negative bacteria), and Aspergillus niger, Candida albicans, and Aspergillus flavus (Fungi). Two analogs, 6c (a 6,8-dichloro analog, MIC([SA]) = 2.5 μg/mL; MIC([ST]) = 2.5 μg/mL) and 7d (a 6,8-dibromo analog, MIC([ST]) = 2.5 μg/mL) were identified as potent antibacterial agents, and two analogs, 6b (a 6-bromo analog, MIC([AF]) = 10 μg/mL) and 6d (a 6,8-dibromo analog, MIC([AF]) = 15 μg/mL; MIC([CA]) = 15μg/mL), were identified as potent antifungal agents. Based on the MIC data, analogs 6b, 6c, 6d, and 7d were identified as the most potent antimicrobial agents in the series.     

Isolation and functional analysis of a 24-residue linear alpha-helical antimicrobial peptide from Korean blackish cicada, Cryptotympana dubia (Homoptera)

A new antimicrobial peptide, cryptonin, was isolated and characterized from the adult Korean blackish cicada, Cryptotympana dubia. It consists of 24 amino acid residues and has a molecular weight of 2,704 Da on mass spectroscopy. The predicted alpha-helical structure analysis and increased helix percent in 40% trifloroethanol of cryptonin suggests that it belongs to the typical linear alpha-helix forming peptide. Binding of the biotin-labeled cryptonin at the surface of E. coli cells and increased influx of propidium iodide in E. coli after cryptonin treatment indicates that it kills microbial cells by binding bacterial cell surfaces and disrupting the cell permeability. Cryptonin showed strong antibacterial (MIC 1.56-25 microg/ml) and antifungal (MIC 3.12-50 microg/ml) activities against tested bacteria and fungi including two antibiotic-resistant bacterial strains; methicilin-resistant S. aureus and vancomycin-resistant Enterococci (MIC 25 microg/ml, each).     

Design and synthesis of diketopiperazine and acyclic analogs related to the caprazamycins and liposidomycins as potential antibacterial agents

A systematic simplification methodology of a class of 6'-N-alkyl-5'-O-aminoribosyl-glycyluridine antibiotics was shown to produce potential antibacterial agents having a novel mechanism of action. Diketopiperazines and acyclic analogs of the caprazamycins (CPZs) and liposidomycins (LPMs) were efficiently synthesized, and their antibacterial activity was evaluated. The diketopiperazine analog 11a and the acyclic analogs 12a and 16a having a palmitoyl group as a lipophilic side chain exhibited moderate antibacterial activities with MICs of 12.5-50 microg/mL. This approach could provide ready access to a range of analogs for the development of potential antibacterial agents.     

Anti-HIV benzylisoquinoline alkaloids and flavonoids from the leaves of Nelumbo nucifera, and structure-activity correlations with related alkaloids

(+)-1(R)-Coclaurine (1) and (-)-1(S)-norcoclaurine (3), together with quercetin 3-O-beta-D-glucuronide (4), were isolated from the leaves of Nelumbo nucifera (Nymphaceae), and identified as anti-HIV principles. Compounds 1 and 3 demonstrated potent anti-HIV activity with EC50 values of 0.8 and <0.8 microg/mL, respectively, and therapeutic index (TI) values of >125 and >25, respectively. Compound 4 was less potent (EC50 2 microg/mL). In a structure-activity relationship study, other benzylisoquinoline, aporphine, and bisbenzylisoquinoline alkaloids, including liensinine (14), negferine (15), and isoliensinine (16), which were previously isolated from the leaves and embryo of Nelumbo nucifera, were evaluated for anti-HIV activity. Compounds 14-16 showed potent anti-HIV activities with EC50 values of <0.8 microg/mL and TI values of >9.9, >8.6, and >6.5, respectively. Nuciferine (12), an aporphine alkaloid, had an EC50 value of 0.8 microg/mL and TI of 36. In addition, synthetic coclaurine analogs were also evaluated. Compounds 1, 3, 12, and 14-16 can serve as new leads for further development of anti-AIDS agents.     

Antimicrobial activity of the extract and isolated compounds from Baccharis dracunculifolia D. C. (Asteraceae)

Baccharis dracunculifolia D.C. (Asteraceae) is the most important plant source of the Brazilian green propolis. Since propolis is known for its antimicrobial activity, the aim of this work was to evaluate the antimicrobial activities of B. dracunculifolia and some of its isolated compounds. The results showed that the leaves extract of B. dracunculifolia (BdE) presents antifungal and antibacterial activities, especially against Candida krusei and Cryptococcus neoformans, for which the BdE showed IC50 values of 65 microg mL(-1) and 40 microg mL(-1), respectively. In comparison to the BdE, it was observed that the green propolis extract (GPE) showed better antimicrobial activity, displaying an IC50 value of 9 microg mL(-1) against C. krusei. Also, a phytochemical study of the BdE was carried out, affording the isolation of ursolic acid (1), 2a-hydroxy-ursolic acid (2), isosakuranetin (3), aromadendrin-4'-methylether (4), baccharin (5), viscidone (6), hautriwaic acid lactone (7), and the clerodane diterpene 8. This is the first time that the presence of compounds 1, 2, and 8 in B. dracunculifolia has been reported. Among the isolated compounds, 1 and 2 showed antibacterial activity against methicillin-resistant Staphylococcus aureus, displaying IC50 values of 5 microg mL(-1) and 3 microg mL(-1), respectively. 3 was active against C. neoformans, showing an IC50 value of 15 microg mL(-1) and a MIC value of 40 microg mL(-1), while compounds 4-8 were inactive against all tested microorganisms. The results showed that the BdE, similar to the GPE, displays antimicrobial activity, which may be related to the effect of several compounds present in the crude extract.