Andrew M. Thompson

Synthesis and structure-activity studies of biphenyl analogues of the tuberculosis drug (6S)-2-nitro-6-{[4-(trifluoromethoxy)benzyl]oxy}-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine (PA-824).

A series of biphenyl analogues of the new tuberculosis drug PA-824 was prepared, primarily by coupling the known (6S)-2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazin-6-ol with iodobenzyl halides, followed by Suzuki coupling of these iodides with appropriate arylboronic acids or by assembly of the complete biaryl side chain prior to coupling with the above alcohol. Antitubercular activity was determined under both replicating (MABA) and nonreplicating (LORA) conditions. para-Linked biaryls were the most active, followed by meta-linked and then ortho-linked analogues. A more detailed study of a larger group of para-linked analogues showed a significant correlation between potency (MABA) and both lipophilicity (CLOGP) and the electron-withdrawing properties of terminal ring substituents ( summation operatorsigma). Selected compounds were evaluated for their efficacy in a mouse model of acute Mycobacterium tuberculosis infection. In vivo activity correlated well with the stability of compounds to microsomal metabolism. Three compounds bearing combinations of lipophilic, electron-withdrawing groups achieved >200-fold higher efficacies than the parent drug.

Synthesis, Reduction Potentials, and Antitubercular Activity of Ring A/B Analogues of the Bioreductive Drug (6S)-2-Nitro-6-{[4-(trifluoromethoxy)benzyl]oxy}-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine (PA-824)

The nitroimidazooxazine S-1 (PA-824) is a new class of bioreductive drug for tuberculosis. A series of related bicyclic nitroheterocycles was synthesized, designed to have a wide range of one-electron reduction potentials E(1) (from -570 to -338 mV, compared with -534 mV for S-1). The observed E(1) values closely correlated with the sigma(m) values of the heteroatom at the 4/8-position of the adjacent six-membered ring. Although the compounds spanned a range of E(1) values around that of S-1, only the nitroimidazothiazines showed significant antitubercular activity (at a similar level of potency), suggesting that E(1) is not the main driver of efficacy. Furthermore, there was a correlation between activity and the formation of imidazole ring-reduced products at the two-electron level, pointing to the potential importance of this reduction pathway, which is determined by the nature of the substituent at the 2-position of the 4-nitroimidazole ring.

Synthesis and Structure−activity Relationships of Antitubercular 2-Nitroimidazooxazines Bearing Heterocyclic Side Chains

Recently described biphenyl analogues of the antituberculosis drug PA-824 displayed improved potencies against M. tuberculosis but were poorly soluble. Heterobiaryl analogues of these, in which the first phenyl ring was replaced with various 5-membered ring heterocycles, were prepared with the aim of identifying potent new candidates with improved aqueous solubility. The compounds were constructed by coupling the chiral 2-nitroimidazooxazine alcohol with various halomethyl-substituted arylheterocycles, by cycloadditions to a propargyl ether derivative of this alcohol, or by Suzuki couplings on haloheterocyclic methyl ether derivatives. The arylheterocyclic compounds were all more hydrophilic than their corresponding biphenyl analogues, and several showed solubility improvements. 1-Methylpyrazole, 1,3-linked-pyrazole, 2,4-linked-triazole, and tetrazole analogues had 3- to 7-fold higher MIC potencies against replicating M. tb than predicted by their lipophilicities. Two pyrazole analogues were >10-fold more efficacious than the parent drug in a mouse model of acute M. tb infection, and one displayed a 2-fold higher solubility.

Synthesis and Structure−Activity Relationships of Aza- and Diazabiphenyl Analogues of the Antitubercular Drug (6S)-2-Nitro-6-{[4-(trifluoromethoxy)benzyl]oxy}-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine (PA-824)

New analogues of antitubercular drug PA-824 were synthesized, featuring alternative side chain ether linkers of varying size and flexibility, seeking drug candidates with enhanced metabolic stability and high efficacy. Both α-methyl substitution and removal of the benzylic methylene were broadly tolerated in vitro, with a biaryl example of the latter class exhibiting an 8-fold better efficacy than the parent drug in a mouse model of acute Mycobacterium tuberculosis infection and negligible fragmentation to an alcohol metabolite in liver microsomes. Extended linkers (notably propenyloxy, propynyloxy, and pentynyloxy) provided greater potencies against replicating M. tb (monoaryl analogues), with propynyl ethers being most effective under anaerobic (nonreplicating) conditions (mono/biaryl analogues). For benzyloxybenzyl and biaryl derivatives, aerobic activity was maximal with the original (OCH(2)) linker. One propynyloxy-linked compound displayed an 89-fold higher efficacy than the parent drug in the acute model, and it was slightly superior to antitubercular drug OPC-67683 in a chronic infection model.

Structure-activity relationships for amide-, carbamate-, and urea-linked analogues of the tuberculosis drug (6S)-2-nitro-6-{[4-(trifluoromethoxy)benzyl]oxy}-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine (PA-824).

Analogues of clinical tuberculosis drug (6S)-2-nitro-6-{[4-(trifluoromethoxy)benzyl]oxy}-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine (PA-824), in which the OCH(2) linkage was replaced with amide, carbamate, and urea functionality, were investigated as an alternative approach to address oxidative metabolism, reduce lipophilicity, and improve aqueous solubility. Several soluble monoaryl examples displayed moderately improved (∼2- to 4-fold) potencies against replicating Mycobacterium tuberculosis but were generally inferior inhibitors under anaerobic (nonreplicating) conditions. More lipophilic biaryl derivatives mostly displayed similar or reduced potencies to these in contrast to the parent biaryl series. The leading biaryl carbamate demonstrated exceptional metabolic stability and a 5-fold better efficacy than the parent drug in a mouse model of acute M. tuberculosis infection but was poorly soluble. Bioisosteric replacement of this biaryl moiety by arylpiperazine resulted in a soluble, orally bioavailable carbamate analogue providing identical activity in the acute model, comparable efficacy to OPC-67683 in a chronic infection model, favorable pharmacokinetic profiles across several species, and enhanced safety.

Synthesis and structure-activity relationships of soluble 8-substituted 4-(2-chlorophenyl)-9-hydroxypyrrolo[3,4-c]carbazole-1,3(2H,6H)-diones as inhibitors of the Wee1 and Chk1 checkpoint kinases.

Pyrrolo[3,4-c]carbazoles bearing solubilising basic side chains at the 8-position retain potent Wee1 and Chk1 inhibitory properties in isolated enzyme assays, and evidence of G2/M checkpoint abrogation in several cellular assays. Co-crystal structure studies confirm that the primary binding to the Wee1 enzyme is as described previously, with the C-8 side chains residing in an area of bulk tolerance.

Repositioning Antitubercular 6-Nitro-2,3-dihydroimidazo[2,1-b][1,3]oxazoles for Neglected Tropical Diseases: Structure-Activity Studies on a Preclinical Candidate for Visceral Leishmaniasis.

6-Nitro-2,3-dihydroimidazo[2,1-b][1,3]oxazole derivatives were initially studied for tuberculosis within a backup program for the clinical trial agent pretomanid (PA-824). Phenotypic screening of representative examples against kinetoplastid diseases unexpectedly led to the identification of DNDI-VL-2098 as a potential first-in-class drug candidate for visceral leishmaniasis (VL). Additional work was then conducted to delineate its essential structural features, aiming to improve solubility and safety without compromising activity against VL. While the 4-nitroimidazole portion was specifically required, several modifications to the aryloxy side chain were well-tolerated e.g., exchange of the linking oxygen for nitrogen (or piperazine), biaryl extension, and replacement of phenyl rings by pyridine. Several less lipophilic analogues displayed improved aqueous solubility, particularly at low pH, although stability toward liver microsomes was highly variable. Upon evaluation in a mouse model of acute Leishmania donovani infection, one phenylpyridine derivative (37) stood out, providing efficacy surpassing that of the original preclinical lead.

Tyrosine Kinase Inhibitors. 20. Optimization of Substituted Quinazoline and Pyrido[3,4- d ]pyrimidine Derivatives as Orally Active, Irreversible Inhibitors of the Epidermal Growth Factor Receptor Family

Structure-activity relationships for inhibition of erbB1, erbB2, and erbB4 were determined for a series of quinazoline- and pyrido[3,4-d]pyrimidine-based analogues of the irreversible pan-erbB inhibitor, canertinib. Cyclic amine bearing crotonamides were determined to provide rapid inhibition of cellular erbB1 autophosphorylation and good metabolic stability in liver microsome and hepatocyte assays. The influence of 4-anilino substitution on pan-erbB inhibitory potency was investigated. Several anilines were identified as providing potent, reversible pan-erbB inhibition. Optimum 4- and 6-substituents with known 7-substituents provided preferred irreversible inhibitors for pharmacodynamic testing in vivo. Quinazoline 54 and pyrido[3,4-d]pyrimidine 71 were identified as clearly superior to canertinib. Both compounds possess a piperidinyl crotonamide Michael acceptor and a 3-chloro-4-fluoroaniline, indicating these as optimized 6- and 4-substituents, respectively. Pharmacokinetic comparison of compounds 54 and 71 across three species selected compound 54 as the preferred candidate. Compound 54 (PF-00299804) has been assigned the nomenclature of dacomitinib and is currently under clinical evaluation.

6-Nitro-2,3-dihydroimidazo[2,1-b][1,3]thiazoles: Facile synthesis and comparative appraisal against tuberculosis and neglected tropical diseases

As part of a quest for backups to the antitubercular drug pretomanid (PA-824), we investigated the unexplored 6-nitro-2,3-dihydroimidazo[2,1-b][1,3]-thiazoles and related -oxazoles. The nitroimidazothiazoles were prepared in high yield from 2-bromo-4-nitroimidazole via heating with substituted thiiranes and diisopropylethylamine. Equivalent examples of these two structural classes provided broadly comparable MICs, with 2-methyl substitution and extended aryloxymethyl side chains preferred; albeit, S-oxidised thiazoles were ineffective for tuberculosis. Favourable microsomal stability data for a biaryl thiazole (45) led to its assessment in an acute Mycobacterium tuberculosis mouse model, alongside the corresponding oxazole (48), but the latter proved to be more efficacious. In vitro screening against kinetoplastid diseases revealed that nitroimidazothiazoles were inactive versus leishmaniasis but showed interesting activity, superior to that of the nitroimidazooxazoles, against Chagas disease. Overall, thio-delamanid (49) is regarded as the best lead.

Chemistry of the mycalamides, antiviral and antitumour compounds from a marine sponge. Part 5. Acid-catalysed hydrolysis and acetal exchange, double bond additions and oxidation reactions

The acid-catalysed degradations of the potent antitumour and antiviral sponge metabolite mycalamide A and a triacetyl derivative have been examined. Acetal exchange reactions, catalytic hydrogenation, epoxidation and oxidation reactions have also been performed on mycalamides A and B. The major products derived from these reactions were characterised and tested for in vitro P388 anti-leukaemia activity and structure–activity relationships were deduced from these results.