Concise Syntheses of the Novel 1H-Pyrrolo[3,2-g]quinazoline Ring System and its [2,3-f] Angular Isomer

A base-mediated synthesis of N-hydroxy- and N-alkoxyindoles from 2-nitrostyrenes

Sequential treatment of alkyl 2-(2-nitroaryl)-2-butenoates with potassium tert-butoxide and an electrophile, such as methyl iodide, benzyl bromide and allyl bromide, afforded N-alkoxyindoles. In related reactions, using sodium tert-pentoxide as the base with or without in situ addition of an electrophile afforded N-alkoxy- and N-hydroxyindoles, respectively. Electrophiles such as dimethylsulfate, p-tosyl chloride, and acetic anhydride afforded moderate yields of the respective N-methoxy-, N-tosyloxy, and N-acetoxyindoles, while methyl iodide, benzyl bromide, and 1-bromohexane failed to form alkylated products using sodium tert-pentoxide as the base.

Synthesis and evaluation of platelet aggregation inhibitory activity of some 3-phenyl-pyrroloquinazolinones

A series of 3-phenyl-2,7-dihydro-1H-pyrrolo[3,2-f]quinazolin-1-one derivatives (3-PPyQZ) was synthesized starting from 5-amino-indoles, via condensation with N-ethoxycarbonylthiobenzamides followed by thermal cyclization. On the basis of their structural analogy with reported anti-thrombin pyrroloquinazolines, the derivatives were first tested for their capacity to inhibit platelet aggregation. Some of them had in vitro inhibitory effects on collagen and thrombin-induced aggregation in the micromolar range, and much higher inhibition than that shown by some phenyl-pyrroloquinolinones. Experiments to determine the mechanism of action of the most potent inhibitor (compound 18) indicated that it acts in at least two sites: one preceding the agonist-induced increase of cytosolic [Ca(2+)], and one following this step of the platelet activation cascade. The compound also inhibited thrombin-evoked protein-Tyr-phosphorylation. Although it is premature to draw definitive conclusions, the present results indicate that 3-PPyQZ structure, with the quite potent inhibitor of platelet aggregation compound 18, might constitute a starting point for the synthesis of potential anti-thrombosis agents.

The reaction of o-alkynylarene and heteroarene carboxaldehyde derivatives with iodonium ions and nucleophiles: a versatile and regioselective synthesis of 1H-isochromene, naphthalene, indole, benzofuran, and benzothiophene compounds

The reaction of o-alkynylbenzaldehydes 1 with different alcohols, silylated nucleophiles 5, electron-rich arenes 10, and heteroarenes 12 in the presence of the reagent IPy(2)BF(4), at room temperature, gave functionalized 4-iodo-1H-isochromenes 2, 6, 11, and 13 in a regioselective manner. When alkynes 16 and alkenes 19 and 20 were used as nucleophiles, a regioselective benzannulation reaction took place to form 1-iodonaphthalenes 17 and 1-naphthyl ketones 18, respectively. Moreover, the latter process has been adapted to accomplish the synthesis of indole, benzofuran, and benzothiophene derivatives (23, 27, and 28, respectively). The three patterns of reactivity observed for the o-alkynylbenzaldehyde derivatives with IPy(2)BF(4) stem from a common iodinated isobenzopyrylium ion intermediate, A, that evolves in a different way depending on the nucleophile present in the reaction medium. A mechanism is proposed and the different reaction pathways observed as a function of the type of nucleophile are discussed. Furthermore, the reaction of the o-hexynylbenzaldehyde 1 b with styrene was monitored by NMR spectroscopy. Compound III, a resting state for the common intermediate in the absence of acid, has been isolated. Its evolution in acid media has been also tested, thereby providing support to the proposed mechanism.

Generation of inhibitor-sensitive protein tyrosine phosphatases via active-site mutations

Protein tyrosine phosphatases (PTPs) catalyze the dephosphorylation of phosphotyrosine, a central control element in mammalian signal transduction. Small-molecule inhibitors that are specific for each cellular PTP would be valuable tools in dissecting phosphorylation networks and for validating PTPs as therapeutic targets. However, the common architecture of PTP active sites impedes the discovery of selective PTP inhibitors. Our laboratory has recently used enzyme/inhibitor-interface engineering to generate selective PTP inhibitors. The crux of the strategy resides in the design of "inhibitor-sensitized" PTPs through protein engineering of a novel binding pocket in the target PTP. "Allele-specific" inhibitors that selectively target the sensitized PTP can be synthesized by modifying broad-specificity inhibitors with bulky chemical groups that are incompatible with wild-type PTP active sites; alternatively, specific inhibitors that serendipitously recognize the sensitized PTP's non-natural pocket may be discovered from panels of "non-rationally" designed compounds. In this review, we describe the current state of the PTP-sensitization strategy, with emphases on the methodology of identifying PTP-sensitizing mutations and synthesizing the compounds that have been found to target PTPs in an allele-specific manner. Moreover, we discuss the scope of PTP sensitization in regard to the potential application of the approach across the family of classical PTPs.

Engineering non-natural inhibitor sensitivity in protein tyrosine phosphatase H1

Protein tyrosine phosphatase H1, a member of the ubiquitous protein tyrosine phosphatase (PTP) superfamily of enzymes, is an important signaling molecule, mutant forms of which have been found in human colorectal cancers. Selective PTPH1 inhibitors would be valuable tools for investigating PTPH1's roles in cellular regulation. However, no PTPH1-specific inhibitors are known. To identify target-selective inhibitors of human PTPH1, we have redesigned a PTPH1/inhibitor interface. Structure-based protein design was used to identify two amino-acid residues, isoleucine 846 and methionine 883, that control PTPH1's sensitivity to oxalylaminoindole PTP inhibitors. Mutation of residues 846 and 883 to alanine and glycine, respectively, conferred novel inhibitor sensitivity onto PTPH1. From a small panel of putative inhibitors, compounds that potently and selectively target the inhibitor-sensitized PTPH1 mutants were identified.

Synthesis of novel paclitaxel prodrugs designed for bioreductive activation in hypoxic tumour tissue

The syntheses and preliminary evaluation of the first potential bioreductive paclitaxel prodrugs are described. These prodrugs were designed as potential candidates in more selective chemotherapy by targeting hypoxic tumour tissue. Aromatic nitro and azide groups were used as the bioreductive trigger. Generation of paclitaxel occurs after reduction and subsequent 1,6-elimination or 1,8-elimination. All prodrugs are stable in buffer and indeed give paclitaxel after chemical reduction of the aromatic nitro or azide functionality. In aerobic cytotoxicity assays several prodrugs exhibit diminished cytotoxicity. These compounds are interesting candidates for further biological evaluation.

2-(oxalylamino)-benzoic acid is a general, competitive inhibitor of protein-tyrosine phosphatases

Protein-tyrosine phosphatases (PTPs) are critically involved in regulation of signal transduction processes. Members of this class of enzymes are considered attractive therapeutic targets in several disease states, e.g. diabetes, cancer, and inflammation. However, most reported PTP inhibitors have been phosphorus-containing compounds, tight binding inhibitors, and/or inhibitors that covalently modify the enzymes. We therefore embarked on identifying a general, reversible, competitive PTP inhibitor that could be used as a common scaffold for lead optimization for specific PTPs. We here report the identification of 2-(oxalylamino)-benzoic acid (OBA) as a classical competitive inhibitor of several PTPs. X-ray crystallography of PTP1B complexed with OBA and related non-phosphate low molecular weight derivatives reveals that the binding mode of these molecules to a large extent mimics that of the natural substrate including hydrogen bonding to the PTP signature motif. In addition, binding of OBA to the active site of PTP1B creates a unique arrangement involving Asp(181), Lys(120), and Tyr(46). PTP inhibitors are essential tools in elucidating the biological function of specific PTPs and they may eventually be developed into selective drug candidates. The unique enzyme kinetic features and the low molecular weight of OBA makes it an ideal starting point for further optimization.