Monocyclic ß-Lactam: A Review on Synthesis and Potential Biological Activities of a Multitarget Core.

A monocyclic ring in their structure characterizes monobactams, a subclass of ß-lactam antibiotics. Many of these compounds have a bactericidal mechanism of action and acts as penicillin and cephalosporins, interfering with bacterial cell wall biosynthesis. The synthesis of novel ß-lactams is an emerging area of organic synthesis research due to the problem of increasing bacterial resistance to existing ß -lactam antibiotics, and, in this way, new compounds have been presented with several structural modifications, aiming to improve biological activities. Among the biological activities studied, the most outstanding are antibacterial, antitubercular, anticholesterolemic, anticancer, antiinflammatory, antiviral, and anti-enzymatic, among others. This review explores the vast number of works related to monocyclic ß-lactams, compounds of great importance in scientific research.

Synthesis, Biological Activity, and Mechanism of Action of 2-Pyrazyl and Pyridylhydrazone Derivatives, New Classes of Antileishmanial Agents.

In this work, we report the antileishmanial activity of 23 compounds based on 2-pyrazyl and 2-pyridylhydrazone derivatives. The compounds were tested against the promastigotes of Leishmania amazonensis and L. braziliensis, murine macrophages, and intracellular L. amazonensis amastigotes. The most potent antileishmanial compound was selected for investigation into its mechanism of action. Among the evaluated compounds, five derivatives [(E)-3-((2-(pyridin-2-yl)hydrazono)methyl)benzene-1,2-diol (2 b), (E)-4-((2-(pyridin-2-yl)hydrazono)methyl)benzene-1,3-diol (2 c), (E)-4-nitro-2-((2-(pyrazin-2-yl)hydrazono)methyl)phenol (2 s), (E)-2-(2-(pyridin-2-ylmethylene)hydrazinyl)pyrazine (2 u), and (E)-2-(2-((5-nitrofuran-2-yl)methylene)hydrazinyl)pyrazine (2 v)] exhibited significant activity against L. amazonensis amastigote forms, with IC50 values below 20 µm. The majority of the compounds did not show any toxic effect on murine macrophages. Preliminary studies on the mode of action of members of this hydrazine-derived series indicate that the accumulation of reactive oxygen species (ROS) and disruption of parasite mitochondrial function are important for the pharmacological effect on L. amazonensis promastigotes.

Quinoxaline Nucleus: A Promising Scaffold in Anti-cancer Drug Discovery.

Heterocyclic compounds are a class of substances, which play a critical role in modern drug discovery being incorporated in the structure of a large variety of drugs used in many different types of diseases. Quinoxaline is an important heterocyclic nucleus with a wide spectrum of biological activities, and recently much attention has been found on anticancer drug discovery based on this class. Owing to the importance of this system, the aim of this review is to provide an update on the synthesis and anticancer activity of quinoxaline derivatives covering articles published between 2010 and 2015.

Different hydrogen-bonded chains in the crystal structures of three alkyl N-[(E)-1-(2-benzyl-idene-1-methyl-hydrazin-yl)-3-hy-droxy-1-oxopropan-2-yl]carbamates.

The crystal structures of three methyl-ated hydrazine carbamate derivatives prepared by multi-step syntheses from l-serine are presented, namely benzyl N-{(E)-1-[2-(4-cyanobenzylidene)-1-methylhydrazinyl]-3-hydroxy-1-oxopro-pan-2-yl}carbamate, C20H20N4O4, tert-butyl N-{(E)-1-[2-(4-cyanobenzylidene)-1-methylhydrazinyl]-3-hydroxy-1-oxopropan-2-yl}carbamate, C17H22N4O4, and tert-butyl N-[(E)-1-(2-benzylidene-1-methylhydrazinyl)-3-hydroxy-1-oxopro-pan-2-yl]carbamate, C16H23N3O4. One of them shows that an unexpected racemization has occurred during the mild-condition methyl-ation reaction. In each crystal structure, the mol-ecules are linked into chains by O-H⋯O hydrogen bonds, but with significant differences between them.

Weak C-H···O and C-H···π hydrogen bonds and π-π stacking interactions in a series of four N'-[(E)-(aryl)methylidene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazides.

Oxazolidin-2-ones are widely used as protective groups for 1,2-amino alcohols and chiral derivatives are employed as chiral auxiliaries. The crystal structures of four differently substituted oxazolidinecarbohydrazides, namely N'-[(E)-benzylidene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C12H12N3O3, (I), N'-[(E)-2-chlorobenzylidene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C12H12ClN3O3, (II), (4S)-N'-[(E)-4-chlorobenzylidene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C12H12ClN3O3, (III), and (4S)-N'-[(E)-2,6-dichlorobenzylidene]-N,3-dimethyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C13H13Cl2N3O3, (IV), show that an unexpected mild-condition racemization from the chiral starting materials has occurred in (I) and (II). In the extended structures, the centrosymmetric phases, which each crystallize with two molecules (A and B) in the asymmetric unit, form A+B dimers linked by pairs of N-H···O hydrogen bonds, albeit with different O-atom acceptors. One dimer is composed of one molecule with an S configuration for its stereogenic centre and the other with an R configuration, and possesses approximate local inversion symmetry. The other dimer consists of either R,R or S,S pairs and possesses approximate local twofold symmetry. In the chiral structure, N-H···O hydrogen bonds link the molecules into C(5) chains, with adjacent molecules related by a 21 screw axis. A wide variety of weak interactions, including C-H···O, C-H···Cl, C-H···π and π-π stacking interactions, occur in these structures, but there is little conformity between them.

Biological evaluation of isoniazid derivatives as an anticancer class.

A series of thirty-two isoniazid derivatives have been evaluated for their activity against four human cancer cell lines with potent cytotoxicity (IC50 ranging from 0.61 to 3.36 µg/mL). The structure-activity relationship (SAR) analysis indicated the number, the positions, and the types of substituents attached to the aromatic ring as being critical factors for the biological activity. Briefly, we observed that the presence of a hydroxyl group on the benzene ring plays an important role in the anticancer activity of this series, especially when it is located in ortho-position. Among the thirty-two compounds, three displayed good cytotoxic activity when compared to the reference drug doxorubicin and are thus being considered leading compounds of this new class.

Design, synthesis and biological evaluation of (E)-2-(2-arylhydrazinyl)quinoxalines, a promising and potent new class of anticancer agents.

A series of forty-seven quinoxaline derivatives, 2-(XYZC6H2CHN-NH)-quinoxalines, 1, have been synthesized and evaluated for their activity against four cancer cell lines: potent cytotoxicities were found (IC50 ranging from 0.316 to 15.749 µM). The structure-activity relationship (SAR) analysis indicated that the number, the positions and the type of substituents attached to the aromatic ring are critical for biological activity. The activities do not depend on the electronic effects of the substituents nor on the lypophilicities of the molecules. A common feature of active compounds is an ortho-hydroxy group in the phenyl ring. A potential role of these ortho-hydroxy derivatives is as N,N,O-tridentate ligands complexing with a vital metal, such as iron, and thereby preventing proliferation of cells. The most active compound was (1: X,Y=2,3-(OH)2, Z=H), which displayed a potent cytotoxicity comparable to that of the reference drug doxorubicin.

Comparison of the structure of (E)-2-(2-benzylidenehydrazinylidene)quinoxaline with those of its chloro- and bromobenzylidene analogues.

(E)-2-(2-Benzylidenehydrazinylidene)quinoxaline, C15H12N4, crystallized with two molecules in the asymmetric unit. The structures of six halogen derivatives of this compound were also investigated: (E)-2-[2-(2-chlorobenzylidene)hydrazinylidene]quinoxaline, C15H11ClN4; (E)-2-[2-(3-chlorobenzylidene)hydrazinylidene]quinoxaline, C15H11ClN4; (E)-2-[2-(4-chlorobenzylidene)hydrazinylidene]quinoxaline, C15H11ClN4; (E)-2-[2-(2-bromobenzylidene)hydrazinylidene]quinoxaline, C15H11BrN4; (E)-2-[2-(3-bromobenzylidene)hydrazinylidene]quinoxaline, C15H11BrN4; (E)-2-[2-(4-bromobenzylidene)hydrazinylidene]quinoxaline, C15H11BrN4. The 3-Cl and 3-Br compounds are isomorphous, as are the 4-Cl and 4-Br compounds. In all of these compounds, it was found that the supramolecular structures are governed by similar predominant patterns, viz. strong intermolecular N-H...N(pyrazine) hydrogen bonds supplemented by weak C-H∙∙∙N(pyrazine) hydrogen-bond interactions in the 2- and 3-halo compounds and by C-H∙∙∙Cl/Br interactions in the 4-halo compounds. In all compounds, there are π-π stacking interactions.

The relevance of new drug combinations for modern tuberculosis treatment--a patent perspective.

Drug combinations (DCs) have been successfully used in different kinds of diseases such as cancer, AIDS, malaria, infectious diseases, asthma, diarrhea, hypertension, neurological disorders, among others. In this context, an important concept in drug discovery relates to the fixed-dose combinations (FDC), which can be defined as a formulation of two or more biologically active substances, combined in a single drug, and available at certain fixed doses. FDC presents several advantages, such as reduced risks of emergence of drug resistant strains, improvement of patient compliance, reduced costs of treatment and a simplified drug supply management, shipping and distribution. Due to the importance of DCs in drug discovery, the purpose of this review is to highlight the importance of this strategy for tuberculosis treatment and also for studies of new promising drug combinations to be used against this disease, specially focused on resistant bacterial strains. Relevant patents concerning combined treatment of tuberculosis are analyzed.

Three 2-(methysulfanyl)nicotinamides.

The molecular conformations of three N-alkyl-2-(methylsulfanyl)nicotinamide derivatives, namely N-cyclohexyl-2-(methylsulfanyl)nicotinamide, C13H18N2OS, (I), N-isopropyl-2-(methylsulfanyl)nicotinamide, C10H14N2OS, (II), in which there are two molecules in the asymmetric unit which were chosen to form a hydrogen-bonded pair, and N-(2-hydroxyethyl)-2-(methylsulfanyl)nicotinamide dihydrate, C9H12N2O2S·2H2O, (III), are compared with those of four unsubstituted N-alkylnicotinamide compounds. The substituted compounds show a higher degree of torsion of the pyridine ring with respect to the amide group than do the unsubstituted compounds, with dihedral angles in the range 40-60° for the former and 20-35° for the latter. In (I) and (II), the supramolecular structure is defined by amide-N to carbonyl-O chains. In (III), the nicotinamide molecules are linked by hydrogen bonds to two water molecules resulting in two linked chains of rings which form the three-dimensional network.

Synthesis and antitubercular activity of novel amino acid derivatives.

In this work, 17 new N-acylhydrazone derivatives of amino acids have been evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H37Rv. The compounds 8b, 8e, 8f, 9a-d, and 10c exhibited an important minimum inhibitory concentration activity between 12.5 and 50 µg/mL, which can be compared with that of the tuberculostatic drug d-cycloserine (20 µg/mL).

tert-Butyl N-((1S)-2-hy-droxy-1-{N'-[(E)-2-hy-droxy-4-meth-oxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate.

The mol-ecule of the title compound, C(16)H(23)N(3)O(6), is twisted about the chiral C atom with the dihedral angle formed between the amide residues being 76.9 (3)°. Overall, the mol-ecule is curved with the terminal organic groups lying to the same side. The conformation about the imine bond [1.291 (5) Å] is E and an intra-molecular O-H⋯N hydrogen bond generates an S(6) ring. In the crystal, O-H⋯O and N-H⋯O hydrogen bonds involving the hy-droxy, amine and carbonyl groups lead to the formation of supra-molecular layers, which stack along the c-axis direction.

Benzyl N-(1-{N'-[(E)-2,3-dihy-droxy-benzyl-idene]hydrazinecarbon-yl}-2-hy-droxy-eth-yl)carbamate dihydrate.

The organic mol-ecule in the title dihydrate, C(18)H(19)N(3)O(6)·2H(2)O, adopts a twisted U-shape with the major twists evident about the chiral C atom [the C-N-C-C torsion angle is -88.2 (4) °] and about the oxygen-benzyl bond [C-O-C-C = 74.2 (4) °]. The conformation about the imine bond [1.290 (4) Å] is E and an intra-molecular O-H⋯N hydrogen bond helps to establish the near coplanarity of the hy-droxy-benzene and hydrazine groups. The crystal packing features O-H⋯O and N-H⋯O hydrogen bonds, leading to two-dimensional supra-molecular arrays in the ab plane with weak C-H⋯π connections between the arrays.

1,3-Dicyclo-hexyl-3-[(pyridin-2-yl)carbon-yl]urea monohydrate from synchrotron radiation.

The title urea derivative crystallizes as a monohydrate, C(19)H(27)N(3)O(2)·H(2)O. The central C(3)N grouping is almost planar (r.m.s. deviation = 0.0092 Å), and the amide and pyridine groups are substanti-ally twisted out this plane [dihedral angles = 62.80 (12) and 34.98 (10)°, respectively]. Supra-molecular double chains propagating along the b-axis direction feature in the crystal packing whereby linear chains sustained by N-H⋯O hydrogen bonds formed between the amide groups are linked by helical chains of water mol-ecules (linked by O-H⋯O hydrogen bonds). The H atom that participates in these water chains is disordered over two positions of equal occupancy. The double chains are connected into a two-dimensional array by C-H⋯O contacts and the layers stack along the a axis.

Synthesis, cytotoxicity, and in vitro antileishmanial activity of mono-t-butyloxycarbonyl-protected diamines.

Leishmania amazonensis is the etiologic agent of the cutaneous and diffuse leishmaniasis. This species is often associated with drug resistance, and the conventional treatments exhibit high toxicity for patients. Therefore, the search for new antileishmanial compounds is urgently needed since there is no vaccine available. In this study, using the in vitro traditional drug screening test, we have analyzed the effects of a series of diaminoalkanes monoprotected with t-butyloxycarbonyl (BOC) against L. amazonensis. Among the 18 tested compounds, 6 exhibited antileishmanial activity (2, 7-9, 17, and 18). Best IC(50) values (10.39 ± 0.27 and 3.8 ± 0.42 µg/mL) were observed for compounds 17 and 18 (H(2)N(CH(2))nNHBoc, n = 10 and 12), respectively. Although those compounds had higher lipophilicity as indicated by their cLog P values, compound 17 was very toxic. Determination of the selective indexes indicated that 50% of the active compounds were very toxic for HepG2 cells. However, compounds 2, 8, and 18 had good lipophilicity and were less toxic among all polyamine derivatives tested. The chemical properties of antileishmanial diamine derivatives, such as lipophilicity and cytotoxicity, are relevant factors for the design of new drugs. A higher lipophilicity is likely to improve the chances of reaching this intracellular parasite.

tert-Butyl N-((1S)-2-hy-droxy-1-{N'-[(1E)-4-meth-oxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate.

The mol-ecule of the title compound, C(16)H(23)N(3)O(5), is twisted about the chiral C atom, the dihedral angle formed between the amide residues being 79.6 (3)°. The conformation about the imine bond [1.278 (5) Å] is E. In the crystal, O-H⋯O and N-H⋯O hydrogen bonding between the hy-droxy, amine and carbonyl groups leads to the formation of supra-molecular layers, which stack along the c-axis direction.

Benzyl N-(2-hy-droxy-1-{N'-[(1E)-2-hy-droxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate.

The mol-ecule of the title compound, C(18)H(19)N(3)O(5), adopts a curved arrangement with the terminal benzene rings lying to the same side. The hydroxyl-benzene ring is close to coplanar with the adjacent hydrazine residue [dihedral angle = 11.14 (12)°], an observation which correlates with the presence of an intra-molecular O-H⋯N hydrogen bond. The benzyl ring forms a dihedral angle of 50.84 (13)° with the adjacent carbamate group. A twist in the mol-ecule, at the chiral C atom, is reflected in the dihedral angle of 80.21 (12)° formed between the amide residues. In the crystal, two-dimensional arrays in the ac plane are mediated by O-H⋯O and N-H⋯O hydrogen bonds.

Benzyl N-(1-{N'-[(E)-2-chloro-benzyl-idene]hydrazinecarbon-yl}-2-hy-droxy-eth-yl)carbamate.

The mol-ecule of the title compound, C(18)H(18)ClN(3)O(4), is twisted about the chiral C atom with the dihedral angle between the two amide residues being 87.8 (5)°, but, overall, it can be described as curved, with the benzene rings lying on the same side of the mol-ecule [dihedral angle = 62.8 (4)°]. The conformation about the imine bond [1.294 (7) Å] is E. In the crystal, a two-dimensional array in the ab plane is mediated by O-H⋯O and N-H⋯O hydrogen bonds as well as C-H⋯Cl inter-actions. The layers stack along the c-axis direction, being connected by C-H⋯.π contacts.

tert-Butyl N-{(1S)-1-[(2,4-dihy-droxy-benzyl-idene)hydrazinecarbon-yl]-2-hy-droxy-eth-yl}carbamate ethanol monosolvate.

The mol-ecule of the title ethanol solvate, C(15)H(21)N(3)O(6)·C(2)H(6)O, adopts a curved shape; the conformation about the imine bond [N=N = 1.287 (3) Å] is E. The amide residues occupy positions almost orthogonal to each other [dihedral angle = 85.7 (2)°]. In the crystal, a network of O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds leads to the formation of supra-molecular arrays in the ab plane with the ethanol mol-ecules lying to the periphery on either side. Disorder in the solvent ethanol mol-ecule was evident with two positions being resolved for the C atoms [site occupancy of the major component = 0.612 (10)].

Benzyl N-((S)-2-hydr-oxy-1-{N'-[(E)-2-methoxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate from synchrotron data.

A U-shaped conformation is found in the title compound, C(19)H(21)N(3)O(5), with the benzene rings lying to the same side of the mol-ecule; the dihedral angle between them is 10.83 (16)°. The dihedral angle formed between the hydrazinecarbonyl and carbamate residues is 68.42 (13)°. The carbonyl groups lie approximately at right angles to each other [O-C⋯C-O pseudo torsion angle of 107.7 (3)°], and the conformation about the C12=N3 bond [1.279 (4) Å] is E. An intra-molecular N(cb)-H⋯O(hy) (cb = carbmate and hy = hydr-oxy) hydrogen bond occurs, generating an S(6) loop. In the crystal, inter-molecular O(h)-H⋯O(ca) (ca = carbon-yl) and N(hz)-H⋯O(ca) (hz = hydrazine) hydrogen bonds lead to the formation of a supra-molecular chain, two mol-ecules thick, which propagates along the a axis; these are connected by C-H⋯O(ca) contacts.