Colin J. Suckling

Mechanistic exploration of the palladium-catalyzed process for the synthesis of benzoxazoles and benzothiazoles.

A convenient one-pot palladium-catalyzed cascade process for the preparation of both benzoxazoles and benzothiazoles has been developed. While these reactions proceed to give similar compounds the mechanisms governing the processes are different as are the experimental conditions employed.

Selective functionalisatlon: Part 10. The nitration of phenols by pyridine derivatives carrying a transferable nitro group

Abstract Pyridinium salts bearing carboxylate side chains and pyridones are shown to react with nitronium tetrafluoroborate or nitrogen dioxide to yield activated intermediates capable of selectively nitrating phenol ortho to the hydroxyl group with virtually complete selectivity and in quantitative yield in aprotic solvents. Although the nitration of phenol itself is exceptionally selective, the nitration of some substituted phenols lead to mixtures of mononitrated products and in especially reactive cases such as 4-methoxyphenol and naphthols, to dinitrated products also. The reactions can be most conveniently carried out on a polymeric support. Spectroscopic evidence is presented to show that intermolecular association between pyridinium salts and the phenols takes place under conditions similar to the reaction conditions and that hydrogen bonding between the phenolic hydroxyl group and acceptor groups on the pyridine ring can also occur. It is suggested that the combination of these two effects leads to the observed selectivity. Attempts to extend the scope of the reaction to other electrophiles and substrates are outlined.

Diversity oriented syntheses of fused pyrimidines designed as potential antifolates

Diversity oriented syntheses of some furo[2,3-d]pyrimidines and pyrrolo[2,3-d]pyrimidines related to folate, guanine, and diaminopyrimidine-containing drugs have been developed for the preparation of potential anti-infective and anticancer compounds. Amide couplings and Suzuki couplings on the basic heterocyclic templates were used, in the latter case yields being especially high using aromatic trifluoroborates as the coupling partner. A new ring synthesis of 6-aryl-substituted deazaguanines bearing 2-alkylthio groups has been developed using Michael addition of substituted nitrostyrenes. Diversity at C-2 has been introduced by oxidation and substitution with a range of amino nucleophiles. The chemical reactivity of these pyrrolopyrimidines with respect to both electrophilic substitution in ring synthesis and nucleophilic substitution for diversity is discussed. Several compounds were found to inhibit pteridine reductases from the protozoan parasites Trypanosoma brucei and Leishmania major at the micromolar level and to inhibit the growth of Trypanosma brucei brucei in cell culture at higher concentrations. From these results, significant structural features required for inhibition of this important drug target enzyme have been identified.

GABA analogues: conformational analysis of effects on [3H]GABA binding to postsynaptic receptors in human cerebellum.

I N ORDER that an analogue of a neurotransmitter substance can bind to the appropriate receptor, the compound must possess the ability to present charged or polarised groups to the receptor in the same relative positions as those in the natural transmitter. Early structure-activity relationship studies of post-synaptic GABA rcceptors in mammalian CNS and in invertebrates showed that a positively charged and a negatively charged or polarised group about 6 A apart on a molecule that possesses some conformational flexibility are requirements for GABA binding.

Measurement of pH changes in an inaccessible aqueous phase during biocatalysis in organic media

SummaryThe pH of the aqueous phase trapped within biocatalyst particles in organic media may be measured using very hydrophobic esters of fluorescein. These remain completely in a pentan-3-one phase, but they ionise there in response to the pH of an equilibrated aqueous phase. They show that the catalyst pH may be significantly shifted from the pre-adjusted value by partitioning of an acidic reactant (N-formyl-tyrosine during chymotrypsin-catalysed esterification) or product (acetic acid during lipase-catalysed ester hydrolysis).

The Synthesis of Fluorine-Containing Pterins

The introduction of fluorine into molecules has been well demonstrated to modify the biological properties significantly1. In heterocyclic compounds this effect is clearly demonstrated through the action of 5-fluorouracil and its nucleosides as inhibitors of thymidylate synthetase. In folic acid derivatives, fluorine has been introduced into the glutamate side chain2 and into the aminobenzoic acid ring to promote nmr observations of interactions with dihydrofolate reductase3. Some side-chain fluorinated pteridinones have been prepared previously4 but analogues of natural products appear to be novel. It would be of interest to investigate the properties of pterins with fluorine as a substituent of the pyrazine ring and also at C-9 of the methylene group. To approach this study we have examined the reactions of 2,4,5-triaminopteridin-6(lH)-one (1) with a number of readily available di-and trifluoromethyl carbonyl compounds. We have also examined the electrostatic potentials of the molecules associated with the introduction of fluorine into the pyrazine ring and its substituents.

Prophylactic and therapeutic treatment with a synthetic analogue of a parasitic worm product prevents experimental arthritis and inhibits IL-1β production via NRF2-mediated counter-regulation of the inflammasome

Rheumatoid arthritis (RA) remains a debilitating autoimmune condition as many patients are refractory to existing conventional and biologic therapies, and hence successful development of novel treatments remains a critical requirement. Towards this, we now describe a synthetic drug-like small molecule analogue, SMA-12b, of an immunomodulatory parasitic worm product, ES-62, which acts both prophylactically and therapeutically against collagen-induced arthritis (CIA) in mice. Mechanistic analysis revealed that SMA-12b modifies the expression of a number of inflammatory response genes, particularly those associated with the inflammasome in mouse bone marrow-derived macrophages and indeed IL-1β was the most down-regulated gene. Consistent with this, IL-1β was significantly reduced in the joints of mice with CIA treated with SMA-12b. SMA-12b also increased the expression of a number of genes associated with anti-oxidant responses that are controlled by the transcription factor NRF2 and critically, was unable to inhibit expression of IL-1β by macrophages derived from the bone marrow of NRF2−/− mice. Collectively, these data suggest that SMA-12b could provide the basis of an entirely novel approach to fulfilling the urgent need for new treatments for RA.

A prototype solid phase synthesis of pteridines and related heterocyclic compounds

The development of a versatile solid phase synthesis of bicyclic polyaza heterocycles including pteridines, purines, and deazapurines is described. The strategy comprises the linking of a pre-formed pyrimidine through a thioether at the 2 or 4 position to a polystyrene resin, the cyclisation of the second ring, and the direct or oxidative cleavage of the product from the resin by nucleophilic substitution. This provides not only for substituent variation in the second ring, but also for variation at the site of cleavage. Limitations in the scope of the methodology are set by the intrinsic reactivity of pyrimidinyl 2- or 4-thioethers which, whilst undergoing ready nitration at C5, are surprisingly difficult to alkylate and acylate.

Carbon-carbon bond formation mediated by papain chemically modified by thiazolium salts

Abstract Alkylation of the active site cysteine with 2-bromomethyl- N-methyl- or 2-bromomethyl-N-benzylthiazolium bromide afforded a protein with no detectable protease activity but the ability to mediate carbon-carbon bond formation with or 6-oxoheptanal as substrate.

Enzyme inhibition by electrophilic cyclopropane derivatives

Abstract Electrophilic cyclopropane-containing compounds have been found in our previous studies to be latent, irreversible inhibitors of horse liver alcohol dehydrogenase, lactate dehydrogenase, and carboxypeptidase A. In addition, cyclopropyl methanols have provided information concerning the mechanism of hydrogen transfer by nicotinamide coenzymes and dehydrogenases. These results are evaluated with the aid of molecular graphics and frontier orbital considerations in the light of the established stereochemical courses of reactions involving cyclopropane ring opening. It is concluded that mechanisms for nucleophilic inhibition consistent with chemical theory and precedent are available at each enzymes active site. Potential enzymic nucleophiles are identifed.