Naphtho[1,8-de][1,2]Oxazin-4-ol: Precursor to 1,2,8-Trisubstituted Naphthalenes and 1-Unsubstituted Naphtho[1,2-d]isoxazole 2-Oxide: A Novel Isomerization of the N-Oxide to Nitrile Oxide en Route to Isoxazol(in)es.

Naphtho[1,8-de][1,2]oxazin-4-ol and its acyl or benzyl derivatives ring open to various 2,8-dihydroxy-1-naphthonitriles, which, through (de)protection protocols and reduction, afford the target (E)-2-hydroxy-8-methoxy-1-naphthaldehyde. This was converted to its corresponding oxime, which was oxidatively o-cyclized with phenyliodine(III) diacetate (PIDA) to 9-methoxynaphtho[1,2-d]isoxazole 2-oxide. The latter, in deuterated DMSO at room temperature, was rearranged to its isomer 2-hydroxy-8-methoxy(naphthalen-1-yl)nitrile oxide. The isomerization was detected by time-course plot 1H NMR spectroscopy and further identified from its 13C NMR and HRMS spectra. The nitrile oxide was stable in (non)deuterated DMSO for at least 18 h. A 3,4-bis(2-hydroxy-8-methoxynaphthalen-1-yl)-1,2,5-oxadiazole 2-oxide, as a dimerization product or an isocyanate as a rearrangement isomer, was ruled out, the former by its HRMS spectrum and the latter by its 1,3-dipolar cycloaddition reactions to substituted isoxazoles.

Novel stable analogues of the neurotensin C-terminal hexapeptide containing unnatural amino acids.

Neurotensin (NT) (pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu) exerts a dual function as a neurotransmitter/neuromodulator in the central nervous system and as a hormone/cellular mediator in periphery. This dual function of NT establishes a connection between brain and peripheral tissues that renders this peptide a central player in energy homeostasis. Many biological actions of NT are mediated through its interaction with three types of NT receptors (NTS receptors). Despite its role in energy homeostasis, NT has a short half-life that hampers further determination of the biological actions of this peptide and its receptors in brain and periphery. The short half-life of NT is due to the proteolytic degradation of its C-terminal side by several endopeptidases. Therefore, it is important to synthesize NT analogues with resistant bonds against metabolic deactivation. Based on these findings, we herein report the synthesis of ten linear, two cyclic and two dimeric analogues of NT with modifications in its structure that improve their metabolic stability, while retaining the ability to bind to NTS receptors. Modifications at position 11 (introduction of D-Tyrosine (OEthyl) [D-Tyr(Et)] or D-1-naphtylalanine [D-1-Nal] were combined with introduction of a L-Lysine or a D-Arginine at positions 8 or 9, and 1-[2-(aminophenyl)-2-oxoethyl]-1H-pyrrole-2-carboxylic acid (AOPC) at positions 7 or 8, resulting in compounds NT4-NT21. AOPC is an unnatural amino acid with promise in applications as a building block for the synthesis of peptidomimetic compounds. To biologically evaluate these analogues, we determined their plasma stability and their binding affinities to type 1 NT receptor (NTS1), endogenously expressed in HT-29 cells, Among the fourteen NT analogues, compounds, NT5, NT6, and NT8, which have D-Tyr(Et) at position 11, bound to NTS1 in a dose-response manner and with relatively high affinity but still lower than that of the natural peptide. Despite their lower binding affinities compared to NT, the NT5, NT6, and NT8 exhibited a remarkably higher stability, as a result of their chemistry, which provides protection from enzymatic activity. These results will set the basis for the rational design of novel NT molecules with improved pharmacological properties and enhanced enzymatic stability.

An Update on the Synthesis of Pyrrolo[1,4]benzodiazepines.

Pyrrolo[1,4]benzodiazepines are tricyclic compounds that are considered "privileged structures" since they possess a wide range of biological activities. The first encounter with these molecules was the isolation of anthramycin from cultures of Streptomyces, followed by determination of the X-ray crystal structure of the molecule and a study of its interaction with DNA. This opened up an intensive synthetic and biological study of the pyrrolo[2,1-c][1,4]benzodiazepines that has culminated in the development of the dimer SJG-136, at present in Phase II clinical trials. The synthetic efforts have brought to light some new synthetic methodology, while the contemporary work is focused on building trimeric pyrrolo[2,1-c][1,4]benzodiazepines linked together by various heterocyclic and aliphatic chains. It is the broad spectrum of biological activities of pyrrolo[1,2-a][1,4]benzodiazepines that has maintained the interest of researchers to date whereas several derivatives of the even less studied pyrrolo[1,2-d][1,4]benzodiazepines were found to be potent non-nucleoside HIV-1 reverse transcriptase inhibitors. The present review is an update on the synthesis of pyrrolo[2,1-c][1,4]benzodiazepines since the last major review of 2011, while the overview of the synthesis of the other two tricyclic isomers is comprehensive.

Self Cycloaddition of o-Naphthoquinone Nitrosomethide to (±) Spiro{naphthalene(naphthopyranofurazan)}-one Oxide: An Insight into its Formation.

2-Hydroxy-1-naphthaldehyde oxime was oxidized by AgO (or Ag2 O), in presence of N-methyl morpholine N-oxide (NMMO), to the title spiro adduct-dimer (±)-Spiro{naphthalene-1(2H),4'-(naphtho[2',1':2,3]pyrano[4,5-c]furazan)}-2-one-11'-oxide by a Diels-Alder(D-A) type self-cycloaddition, through the agency of an o-naphthoquinone nitrosomethide (o-NQM). Moreover, 2-hydroxy-8-methoxy-1-naphthaldehyde oxime was prepared and subjected to the same oxidation conditions. Its sterically guided result, 9-methoxynaphtho[1,2-d]isoxazole, was isolated, instead of the expected spiro adduct. The peri intramolecular H bonding in the oxime is considered to have a key contribution to the outcome. Geometry and energy features of the oxidant- and stereo-guided selectivity of both oxidation outcomes have been explored by DFT, perturbation theory and coupled cluster calculations. The reaction free energy of the D-A intermolecular cycloaddition is calculated at -82.0 kcal/mol, indicating its predominance over the intramolecular cyclization of ca. -37.6 kcal/mol. The cycloaddition is facilitated by NMMO through dipolar interactions and hydrogen bonding with both metal complexes and o-NQM. The 8(peri)-OMe substitution of the reactant oxime sterically impedes formation of the spiro adduct, instead it undergoes a more facile cyclodehydration to the isoxazole structure by ca. 4.9 kcal/mol.

The Isoxazole Ring and Its N-Oxide: A Privileged Core Structure in Neuropsychiatric Therapeutics.

Mental disorders are neuropsychiatric conditions that are marked by unusual or irregular thinking, feelings, or behavior, and lead to distress and/or impaired functions. Major psychiatric conditions are depression, anxiety, and psychoses of various types. Their etiopathogeneses, of a primary or secondary origin, are associated with genetic and environmental factors. They are commonly treated with psychoactive drugs (also known as psychotropics), which target serotonin, dopamine, norepinephrine, glutamate, and nuclear receptors (NRs), including retinoic acid receptor-related orphan receptors (RORs) and other receptors in the central nervous system (CNS). Herein we present a diverse array of isoxazole derivatives, among which are some prominent marketed drugs. Some of the derivatives and forms, including N-oxides, are under either (pre)clinical evaluation or patent protection as new generation of psychotropics, and a few have effective blood-brain barrier (BBB) permeability. Various drug-like isoxazol(in)es and their structural features and efficiency, modified through scaffold hopping, are described and discussed in the context of treating neuropsychiatric conditions.

Novel synthesis of 3-substituted 2,3-dihydrobenzofurans via ortho-quinone methide intermediates generated in situ.

A new method is presented for the regioselective one-pot synthesis of 3-substituted 2,3-dihydrobenzofurans from 2-bromo-1-{2-[(triisopropylsilyl)oxy]phenyl}ethyl nitrate by fluoride-induced desilylation leading to o-quinone methide generation, Michael addition of different C, N, O, and S nucleophiles, and intramolecular 5-exo-tet elimination of a bromide anion. The method has potential synthetic applications in drug discovery.

Mild and rapid method for the generation of ortho-(naphtho)quinone methide intermediates.

A new mild method has been devised for generating o-(naphtho)quinone methides via fluoride-induced desilylation of silyl derivatives of o-hydroxybenzyl(or 1-naphthylmethyl) nitrate. The reactive o-(naphtho)quinone methide intermediates were trapped by C, O, N, and S nucleophiles and underwent "inverse electron-demand" hetero-Diels-Alder reaction with dienophiles to give stable adducts. The method has useful potential application in natural product synthesis and drug research.

Synthesis and study of 2-(pyrrolesulfonylmethyl)-N-arylimines: a new class of inhibitors for human glutathione transferase A1-1.

Overexpression of human GSTA1-1 in tumor cells is part of MDR mechanisms. We report on the synthesis of 11 pyrrole derivatives as hGSTA1-1 inhibitors starting from 1-methyl-2-[(2-nitrobenzylsulfanyl]-1H-pyrrole. Molecular modeling revealed two locations in the enzyme H binding site: the catalytic primary one accommodating shorter and longer derivatives and the secondary one, where shorter derivatives can occupy. Derivative 9, displaying the highest inhibition and bearing a p-nitroarylimino moiety, and derivative 4, lacking this moiety, were studied kinetically. Derivative 9 binds (K(i(9)) = 71 ± 4 µM) at the primary site competitively vs CDNB. Derivative 4 binds (K(i(4)) = 135 ± 27 µM) at the primary and secondary sites, allowing the binding of a second molecule (4 or CDNB) leading to formation of unreactive and reactive complexes, respectively. The arylmethylsulfonylpyrrole core structure is a new pharmacophore for hGSTA1-1, whereas its derivative 9 may serve as a lead structure.

Novel thermal and microwave-assisted facile route to naphthalen-2(1H)-ones via an oxidative alkoxylation-ring-opening protocol.

Several novel 1,1-disubstituted-8-hydroxynaphthalen-2(1H)-ones have been efficiently synthesized via a two-step sequence from 2-hydroxy-1-naphthaldehyde oxime. The methodology involves oxidative ring closure and alkoxylation to 3a-alkoxynaphtho[1,8-de][1,2]oxazin-4(3aH)-ones, followed by thermal ring-opening. Both thermal and microwave irradiation conditions were used. A novel one-pot reaction of oxime to 8-isopropoxynaphthalene-1,7-diol using microwave irradiation is also reported.

Action of a novel pyrrolo[1,2-c][1.3]benzodiazepine on the viability of Jurkat and neuronal/glial cells.

We have designed and synthesized several structural isomers of anthramycin (heterocycles 2, 3, 5, 6, and 8) and found that, in particular, pyrrolobenzodiazepine 8 induces DNA cleavage and formation of small fragments of DNA. The cytotoxic effects of 8 were manifested with both non-transformed primary neuronal/glial cells and transformed Jurkat cells. The other compounds did not change the viability either of transformed or of non-transformed cells, and induced DNA cleavage to a lesser extent.