Ring-substituted quinolines as potential anti-tuberculosis agents

We report in vitro antimycobacterial properties of ring-substituted quinolines (series 1-4) constituting 56 analogues against drug-sensitive and drug-resistant M. tuberculosis H37Rv strains. The most effective compounds 2h (R1 = R2 = c-C6H11, R3 = NO2, series 1) and 13g (R1 = OC7H15, R2 = NO2, series 4) have exhibited an MIC value of 1 microg/mL against drug-sensitive M. tuberculosis H37Rv strain that is comparable to first line anti-tuberculosis drug, isoniazid. Selected analogues (2d, 2g, 2h, 4e, 6b, 13b, 13g, and 14e, MIC: < or = 6.25 microg/mL) upon further evaluation against single-drug-resistant (SDR) strains of M. tuberculosis H37Rv have produced potent efficacy in the range between 6.25 and 50 microg/mL.     

Synthesis, anti-tuberculosis activity, and 3D-QSAR study of ring-substituted-2/4-quinolinecarbaldehyde derivatives

We have previously identified ring-substituted quinolines as a new structural class of anti-tuberculosis agents. In our ongoing efforts at structural optimization of this class, four series of ring-substituted-2/4-quinolinecarbaldehyde derivatives were synthesized. All twenty-four compounds were synthesized using short and convenient one to two high yielding steps. The newly synthesized compounds were tested in vitro against drug-sensitive Mycobacterium tuberculosis H37Hv strain. Several derivatives were found to be promising inhibitors of M. tuberculosis. For example, derivatives 4a-c (Series 2), 7a-d (Series 3), and 8a-b (Series 4) displayed >90% inhibition at 6.25 microg/mL in the primary assay. The most active compounds, N-(2-fluorophenyl)-N'-quinolin-2-ylmethylene-hydrazine (4a), N-(2-adamantan-1-yl-quinolin-4-ylmethylene)-N'-(4-fluorophenyl)hydrazine (7c), and N-(2-cyclohexyl-quinolin-4-ylmethylene)-N'-(2-fluorophenyl)hydrazine (8a), exhibited 99% inhibition at the lowest tested concentration of 3.125 microg/mL against drug-sensitive M. tuberculosis H37Rv strain. The similarity index based on steric and electrostatic features of the molecules was used, in conjunction with principal component analysis and linear discriminant analysis, successively to classify the molecules based on their activity into two classes. This classification method gives us confidence in predicting the activity class of any new unsynthesized molecule belonging to these series.     

3D-QSAR study of ring-substituted quinoline class of anti-tuberculosis agents

A 3D-QSAR analysis of a new class of ring-substituted quinolines with anti-tuberculosis activity has been carried out by three methods-Comparative Molecular Field Analysis (CoMFA), CoMFA with inclusion of a hydropathy field (HINT), and Comparative Molecular Similarity Indices Analysis (CoMSIA). The conformation of the molecules was generated using a simulated annealing protocol and they were superimposed using features common to the set with database alignment (SYBYL) and field fit methods. Several statistically significant CoMFA, CoMFA with HINT, and CoMSIA models were generated. Prediction of the activity of a set of test molecules was the best for the CoMFA model generated with database alignment. Based upon the information contained in the CoMFA model, we have identified some novel features that can be incorporated into the quinoline framework to improve the activity.     

Binding of beta-carbolines at 5-HT(2) serotonin receptors

A series of ring-substituted (i.e., methoxy and bromo) 3,4-dihydro- and 1,2,3,4-tetrahydro-β-carbolines was examined at 5-HT_2A and 5-HT_2C serotonin receptors. Whereas most of the methoxy-substituted derivatives typically displayed affinities similar to their unsubstituted parents, certain (particularly 8-substituted) bromo derivatives displayed enhanced affinity. A binding profile was obtained for selected β-carbolines.     

3-Phenylpropenes as mechanism-based inhibitors of dopamine beta-hydroxylase: evidence for a radical mechanism

A series of ring-substituted 3-phenylpropenes has been examined as mechanism-based inhibitors for the copper protein dopamine beta-hydroxylase. p-HO-, p-CH3O-, m-HO-, m-CH3O-, p-Br-, and p-CN-substituted phenylpropenes all inactivate the enzyme under turnover conditions, requiring ascorbate and oxygen. Replacement of the benzylic hydrogens in 3-(p-hydroxyphenyl)propene with deuterium results in a kinetic isotope effect of 2.0 on kinact/KO2 but in no effect on the partition ratio, Vmax/kinact, consistent with a stepwise mechanism for hydrogen abstraction and oxygen insertion. The partition ratio is unchanged in the pH range from 4.5 to 7.1. Determination of the kinetics of inactivation and the partition ratios for each of these ring-substituted phenylpropenes has allowed determination of the respective V/KO2 values. A linear free energy plot of these values as a function of sigma+ gives a rho value of -1.2, while the partition ratios show only a slight decrease upon going electron-withdrawing groups. The results are consistent with a mechanism for dopamine beta-hydroxylase in which a hydrogen atom is abstracted to form a benzylic radical, which then partitions between hydroxylation and enzyme inactivation.     

Antitubercular nitrofuran isoxazolines with improved pharmacokinetic properties

A series of tetracyclic nitrofuran isoxazoline anti-tuberculosis agents was designed and synthesized to improve the pharmacokinetic properties of an initial lead compound, which had potent anti-tuberculosis activity but suffered from poor solubility, high protein binding and rapid metabolism. In this study, structural modifications were carried on the outer phenyl and piperidine rings to introduce solubilizing and metabolically blocking functional groups. The compounds generated were evaluated for their in vitro antitubercular activity, bacterial spectrum of activity, solubility, permeability, microsomal stability and protein binding. Pharmacokinetic profiles for the most promising candidates were then determined. Compounds with phenyl morpholine and pyridyl morpholine outer rings were found to be the most potent anti-tuberculosis agents in the series. These compounds retained a narrow antibacterial spectrum of activity, with weak anti-Gram positive and no Gram negative activity, as well as good activity against non-replicating Mycobacterium tuberculosis in a low oxygen model. Overall, the addition of solubilizing and metabolically blocked outer rings did improve solubility and decrease protein binding as designed. However, the metabolic stability for compounds in this series was generally lower than desired. The best three compounds selected for in vivo pharmacokinetic testing all showed high oral bioavailability, with one notable compound showing a significantly longer half-life and good tolerability supporting its further advancement.     

Discovery of novel isoxazolines as anti-tuberculosis agents

Nitrofuranyl isoxazolines with increased proteolytic stability over nitrofuranyl amides were designed and synthesized leading to discovery of several compounds with potent in vitro anti-tuberculosis activity. However, their in vivo activity was limited by high protein binding and poor distribution. Consequently, a series of non-nitrofuran containing isoxazolines were prepared to determine if the core had residual anti-tuberculosis activity. This led to the discovery of novel isoxazoline 12 as anti-tuberculosis agent with a MIC(90) value of 1.56microg/mL.     

Binding of beta-carbolines at imidazoline I2 receptors: a structure-affinity investigation

A series of ring-substituted (i.e., methoxy and bromo) 3,4-dihydro- and 1,2,3,4-tetrahydro-beta-carbolines was examined at I(2) imidazoline receptors, as was the effect of ring-opening, ring-expansion, and translocation of the piperidinyl nitrogen atom. Several analogues were identified that bind with K(i) <20 nM at I(2) sites and with reduced affinity at alpha(2)-adrenergic receptors, and 1,2,3,4-tetrahydro-gamma-carbolines were identified as a novel class of I(2) imidazoline receptor ligand.     

Effect of pH on the transient reduction of pig-plasma benzylamine oxidase by benzylamine derivatives.

1. The transient kinetics of reduction of the 470-nm absorption band in benzylamine oxidase by substrate at different pH values between 6 and 10 have been studied by stopped-flow techniques, and substituent effects on kinetic parameters for the reduction process have been examined using a series of ring-substituted benzylamine derivatives as the substrates. 2. Reduction of the enzyme by substrate takes place in two kinetically distinguishable steps, with the intermediate formation of an enzyme-substrate complex in which the substrate appears to be covalently bound through its amino group to the prosthetic group of the enzyme, possibly in the form of an amine-pyridoxal Schiff-base. 3. The apparent stability of the enzyme-substrate complex shows no obvious dependence on the electronic properties of the amine substrates, but is strongly pH-dependent in a way suggesting that substrate-binding involves the non-protonated amines, exclusively, and requires the presence of the acid form of an ionizing group in the enzyme with apparent pKa of 8.8. 4. Reduction of the enzymatic 470-nm chromophore and release of the aldehyde product of the catalytic process are rate-limited by the same monomolecular reaction step involving the enzyme-substrate complex. Rate constants for the rate-limiting reaction exhibit no significant dependence on pH between 6 and 10, but correlate with Hammett sigma-values for the ring-substituted benzylamine derivatives tested, yielding a phi-value of + 0.3.     

Gas-liquid Chromatographic Separation of Amine Enantiomers as N-Trifluoroacetyl-L-prolylamide Derivatives

Separation of asymmetric amines by derivatization to the corresponding amides with N-trifluoroacetyl-L-prolyl chloride was carried out by gas-liquid chromatography, and the structure-separation relationship was studied. For a series of ring-substituted 1-phenyl or naphthylalkylamines, diastereoisomeric amides were better resolved on a relatively polar column than on a nonpolar column with the L(+) forms eluted before the L(?) forms and the separation was poorer as the alkyl group attached to the asymmetric carbon atom was varied from isopropyl to methyl to n-propyl to isobutyl. On the contrary, for another series of ring-substituted 1,2-diphenylethylamines, the isomeric amides were better resolved on a nonpolar column than on a polar column, the L(+) forms being eluted with longer retention than the L(?) forms, and the separation was better when the alkyl group substituted for a hydrogen of the phenyl group at α-position was bulkier. Furthermore, the optical purity of asymmetric amines was determined by measuring gas chromatographic peak areas of diastereoisometic amide components.     

New rifabutin analogs: synthesis and biological activity against Mycobacterium tuberculosis

The synthesis, structure, and biological evaluation of a series of novel rifamycin derivatives, Rifastures (RFA) with potent anti-tuberculosis activity are presented. Some of these derivatives showed higher in vitro activity than rifabutin and rifampicin against not only Mycobacterium tuberculosis strains but also against MAC and Mycobacterium kansasii.     

Modification of the side chain of micromolide, an anti-tuberculosis natural product

This paper describes a series of modifications of the side chain of micromolide, an anti-tuberculosis natural product. Most of the synthesized compounds showed significantly decreased activities, which suggests that the long aliphatic side chain of micromolide and its double bond are essential to its activity.     

Ring-substituted 11-oxo-11H-indeno[1,2-b]quinoline-6-carboxamides with similar patterns of cytotoxicity to the dual topo I/II inhibitor DACA

A series of ring-substituted analogues of the topoisomerase inhibitor 11-oxo-11H-indeno[1,2-b]quinoline-6-carboxamides was prepared and evaluated. The compounds were prepared by Pfitzinger reaction of the appropriate isatin-7-carboxylic acids and 1-indanones, followed by selective thermal decarboxylation of the resulting tetracyclic diacids, subsequent oxidation of the methylene group with alkaline permanganate under carefully controlled conditions, and 1,1'-carbonyldiimidazole-induced amidation. The compounds were evaluated in a panel of cell lines in culture. The largest increases in cytotoxicity (five to tenfold) were shown by 4-substituted analogues, with the 4-Cl derivative having an IC₅₀ of 8 nM against the Lewis lung carcinoma.     

Two groups of thermophilic amino acid aminotransferases exhibiting broad substrate specificities for the synthesis of phenylglycine derivatives

Thirty two thermophilic amino acid aminotransferases (AATs) were expressed in Escherichia coli as soluble and active proteins. Based on their primary structures, the 32 AATs were divided into four phylogenetic groups (classes I, II, IV, and V). The substrate specificities of these AATs were examined, and 12 AATs were found capable of synthesizing ring-substituted phenylglycine derivatives such as hydroxyl-, methoxy-, and fluorophenylglycines. Eleven out of the 12 AATs were enzymes belonging to two phylogenetic groups namely, one subgroup of the class I family and the class IV family. AATs in these two groups may thus be useful for the synthesis of a variety of ring-substituted phenylglycine derivatives.     

Synthesis of new and potent analogues of anti-tuberculosis agent 5-nitro-furan-2-carboxylic acid 4-(4-benzyl-piperazin-1-yl)-benzylamide with improved bioavailability

Previously, the lead compound 5-nitro-furan-2-carboxylic acid 4-(4-benzyl-piperazin-1-yl)-benzylamide was identified in our anti-tuberculosis drug discovery program. Although this compound demonstrated excellent in vitro activity, it did not meet the expected in vivo profiles due to structural features that resulted in rapid metabolic cleavage and poor absorption, which therefore limited its bioavailability. In efforts to increase the bioavailability, a new series of analogues was successfully synthesized using three modification schemes: replacement of the benzyl group on the piperazine C-ring with carbamate and urea functional groups; introduction of a nitrogen atom into the aromatic ring-B; and expansion of the ring-B to a bicyclic tetrahydroisoquinoline moiety. These modifications retained strong activity and in some case gained superior anti-tuberculosis activity, increased absorption, and serum half life.     

Thymidine and thymidine-5'-O-monophosphate analogues as inhibitors of Mycobacterium tuberculosis thymidylate kinase

The affinity of a series of 2', 3'- and 5-modified thymidine analogues for Mycobacterium tuberculosis thymidine monophosphate kinase (TMPKmt) was evaluated. The affinities of several non-phosphorylated analogues are in the same order of magnitude as those of their phosphorylated congeners. In view of drug delivery problems associated with phosphorylated compounds, these 'free' nucleosides seem more promising leads in the search of TMPKmt inhibitors as novel anti-tuberculosis agents.     

Effects of chronic treatment of rats with "designer" amphetamines on brain regional monoamines.

(+)-Amphetamine and two structurally related analogues, 4-methoxyamphetamine and a recent "designer drug," 4-ethoxyamphetamine, were given to rats via subcutaneous osmotic minipumps for 1-14 days. Regional brain levels of the drugs as well as monoamine neurotransmitters and some of their major acidic metabolites were determined. Amphetamine produced depletions of dopamine in the striatum after at least 3 days of treatment but not in the nucleus accumbens of olfactory tubercle, even after 14 days of treatment. In contrast, the two ring-substituted amphetamine analogues increased levels of the monoamines and decreased levels of their acid metabolites. These data indicate that the two ring-substituted amphetamine analogues, at least one of which is a potent hallucinogen, have potent monoamine oxidase inhibition properties that are sustained during chronic treatment. Furthermore, these two compounds do not share amphetamine's regionally selective neurotoxic effects on dopamine-releasing terminals, even though brain and striatal drug levels are the same or higher than those of amphetamine.     

结核病新抗生素靶标和抑制剂研发

随着结核病耐药现象越来越严重,迫切需要开发新型抗结核药物,而大部分的药物开发主要依赖于新型的抗生素靶标的发现。文中综述了2016年以来新出现的具有开发为抗结核药物潜力的新化合物,并重点阐述了这些新化合物所针对的抗生素靶标,将有助于针对这些靶标进一步开发新型抗结核药物。     

儿茶素类化合物的抗结核活性研究进展

近年来,耐多药结核病(multidrug-resistant tuberculosis,MDR-TB)的出现及人类免疫缺陷病毒(human immunodeficiency virus,HIV)与结核分枝杆菌合并感染日益增多,使结核病的防治面临更加严峻的挑战,人们急需开发新型抗结核药物及天然低毒的辅助治疗药物。绿茶中的儿茶素类化合物具有多种生物活性,对多种疾病有一定的辅助疗效。多项研究显示,儿茶素类化合物也具有抗结核活性,其机制包括抑制二氢叶酸还原酶活性、影响分枝菌酸及细胞壁的合成、下调富含色氨酸天冬氨酸的膜蛋白(tryptophan-aspartate containing coat protein,TACO)基因表达以抑制结核分枝杆菌的胞内寄生,降低氧化应激水平,下调结核分枝杆菌85B蛋白和宿主肿瘤坏死因子α(tumor necrosis factor α,TNF-α)表达,从而改善炎症水平。有研究显示,喝绿茶可降低结核分枝杆菌感染风险,儿茶素类化合物可辅助治疗结核病并与抗结核药物有协同治疗作用,但目前对其作用机制的研究还不够深入,需进一步探讨。