Novel non-classical C9-methyl-5-substituted-2,4-diaminopyrrolo[2,3-d]pyrimidines as potential inhibitors of dihydrofolate reductase and as anti-opportunistic agents

Synthesis of 2,4-Diaminopyrimidine Core-Based Derivatives and Biological Evaluation of Their Anti-Tubercular Activities

Tuberculosis (TB) is a chronic, potentially fatal disease caused by Mycobacterium tuberculosis (Mtb). The dihyrofolate reductase in Mtb (mt-DHFR) is believed to be an important drug target in anti-TB drug development. This enzyme contains a glycerol (GOL) binding site, which is assumed to be a useful site to improve the selectivity towards human dihyrofolate reductase (h-DHFR). There have been previous attempts to design drugs targeting the GOL binding site, but the designed compounds contain a hydrophilic group, which may prevent the compounds from crossing the cell wall of Mtb to function at the whole cell level. In the current study, we designed and synthesized a series of mt-DHFR inhibitors that contain a 2,4-diaminopyrimidine core with side chains to occupy the glycerol binding site with proper hydrophilicity for cell entry, and tested their anti-tubercular activity against Mtb H37Ra. Among them, compound 16l showed a good anti-TB activity (MIC = 6.25 μg/mL) with a significant selectivity against vero cells. In the molecular simulations performed to understand the binding poses of the compounds, it was noticed that only side chains of a certain size can occupy the glycerol binding site. In summary, the novel synthesized compounds with appropriate side chains, hydrophobicity and selectivity could be important lead compounds for future optimization towards the development of future anti-TB drugs that can be used as monotherapy or in combination with other anti-TB drugs or antibiotics. These compounds can also provide much information for further studies on mt-DHFR. However, the enzyme target of the compounds still needs to be confirmed by pure mt-DHFR binding assays.

Dihydrofolate reductase as a therapeutic target for infectious diseases: opportunities and challenges

Infectious diseases caused by parasites continue to take a massive toll on human health in the poor regions of the world. Filling the anti-infective drug-discovery pipeline has never been as challenging as it is now. The organisms responsible for these diseases have interesting biology with many potential biochemical targets. Inhibition of metabolic enzymes has been established as an attractive strategy for anti-infectious drug development. In this field, dihydrofolate reductase (DHFR) is an important enzyme in nucleic and amino acid synthesis and an extensively studied drug target over the past 50 years. The challenges for novel DHFR inhibition-based chemotherapeutics for the treatment of infectious diseases are now focused on overcoming the resistance problem as well as cost–effectiveness. Each year, the large number of literature citations attest the continued popularity of DHFR. It becomes truly the ‘enzyme of choice for all seasons and almost all reasons’. Herein, we summarize the opportunities and challenges in developing novel lead based on this target.

A homogeneous, recyclable polymer support for Rh(I)-catalyzed C-C bond formation

A robust and practical polymer-supported, homogeneous, recyclable biphephos rhodium(I) catalyst has been developed for C-C bond formation reactions. Control of polymer molecular weight allowed tuning of the polymer solubility such that the polymer-supported catalyst is soluble in nonpolar solvents and insoluble in polar solvents. Using the supported rhodium catalysts, addition of aryl and vinylboronic acids to the electrophiles such as enones, aldehydes, N-sulfonyl aldimines, and alkynes occurs smoothly to provide products in high yields. Additions of terminal alkynes to enones and industrially relevant hydroformylation reactions have also been successfully carried out. Studies show that the leaching of Rh from the polymer support is low and catalyst recycle can be achieved by simple precipitation and filtration.

Design, synthesis, biological evaluation and computational investigation of novel inhibitors of dihydrofolate reductase of opportunistic pathogens

The present work deals with design, synthesis and biological evaluation of novel, diverse compounds as potential inhibitors of dihydrofolate reductase (DHFR) from opportunistic microorganisms; Pneumocystis carinii (pc), Toxoplasma gondii (tg) and Mycobacterium avium (ma). A set of 14 structurally diverse compounds were designed with varying key pharmacophoric features of DHFR inhibitors, bulky distal substitutions and different bridges joining the distal part and 2,4-diaminopyrimidine nucleus. The designed compounds were synthesized and evaluated in enzyme assay against pc, tg and ma DHFR. The rat liver (rl) DHFR was used as mammalian standard. As the next logical step of the project, flexible molecular docking studies were carried out to predict the binding modes of these compounds in pcDHFR active site and the obtained docked poses were post processed using MM-GBSA protocol for prediction of relative binding affinity. The predicted binding modes were able to rationalize the experimental results in most cases. Of particular interest, both the docking scores and MM-GBSA predicted Delta G(bind) were able to distinguish between the active and low active compounds. Furthermore, good correlation coefficient of 0.797 was obtained between the IC(50) values and MM-GBSA predicted Delta G(bind). Taken together, the current work provides not only a novel scaffold for further optimization of DHFR inhibitors but also an understanding of the specific interactions of inhibitors with DHFR and structural modifications that improve selectivity.