Introduction DHFR is an important enzyme
DHFR is an important enzyme in both mammals and microorganism including Mycobacterium tuberculosis (Mtb). It catalyzes folic hydrocort conversion to dihydro and tetrahydro folic acid which is a crucial step in folate pathway . Inhibition of folate pathway leads to interruption of thymidine supply resulting cell death. Folate metabolism plays an essential role in the biosynthesis of purines and pyrimidines and therefore in the nucleic acid biosynthesis for all the living organisms and is thus directly or indirectly involved in the processes of cell reproduction . Tuberculosis (TB) is a top infectious disease killer worldwide. In 2016 global statistics showed that 10.4 million suffered with TB and 1.7 million died from the disease. TB is a leading killer of HIV-positive people: in 2016, 1 in 3 HIV deaths was due to TB. Globally in 2016, an estimated 490,000 people developed multidrug-resistant TB (MDR-TB) . New forms of MDR-TB and extensively drug resistant TB (XDR-TB), pose new challenge for medicinal chemist. To address new threat, there is an urgent need to develop new anti-TB drugs on novel targets having minimum cross resistance with existing drugs. Thus, new anti-tuberculosis agents which could act via unique mechanism is need of the hour. DHFR being crucial for survival of microorganism has been explored extensively as drug target for example methotrexate , trimethoprim  and Br-WR99210  an analogue of the antimalarial agent R99210  (Fig. 1) have been found effective clinically against tuberculosis. However, all clinically effective DHFR inhibitors are non-selective, and inhibit both human and pathogenic DHFR more or less to a similar extent.
Mycobacterium (Mtb) and human (h) DHFRs show 26% structure similarity, but their active sites are not identical . Dissimilarities in the enzymatic constitution of the microorganisms and mammals, forms the basis for design of selective inhibitors devoid of toxicity to human cells . Therefore a comparative computational study will help design selective Mtb-DHFR inhibitors. The structural based virtual screening (SBVS) has gained enormous attention and success in pharmaceutical industry over the past few decades for discovering novel drugs . The aim of this study was to develop a novel series of selective Mtb-DHFR inhibitors as antitubercular agents using SBVS and synthetic approach (Fig. 2).
Results and discussion
Conclusion By using in silico approach, the glycerol binding site of Mtb-DHFR binding pocket was exploited successfully to identify and develop novel inhibitors for same. Based on the virtual screeninghit 1 was obtained, and a seriesof molecules was designed, by using different substituents at 3, 5 position of indolemoiety of hit 1.CompoundIND-07was developed as novel selective inhibitors of Mtb-DHFR. It contains a novel central core (1-(1-benzyl-5-hydroxy-2-methyl-1H-indol-3-yl) ethanone), which will significantly expand the chemical space of novel Mtb-DHFRinhibitors. This compound did show selectivity againstMtb-DHFRand can be used as a lead compound for further optimization. Further, the present findings will help in designing novel Mtb-DHFR inhibitors in future to improve the selectivity of compounds againstMtb-DHFR. Software used: (a) Schrödinger Suite 2017 Protein Preparation Wizard; LLC, New York, NY, Glide 7.1 Schrödinger, LLC; New York, NY, 2017, LigPrep, version 4.6, Schrödinger, LLC, New York, NY, 2017. (b) Molinspiron property calculation program.
Cryptosporidiosis is a gastrointestinal illness, which in humans is primarily caused by two parasites, () and (). is capable of surviving without a host for many months and at a wide range of temperatures, and are well known to infect large groups of people when food or water supplies become contaminated., Healthy individuals experience gastrointestinal distress that can last for two or more weeks, while infection rates are higher and more severe in children, the elderly, and especially in immunocompromised individuals., For example, people with HIV/AIDS are more likely to develop severe symptoms, including persistent, debilitating and possibly fatal diarrhea and wasting.In addition, a major impact of cryptosporidiosis is also felt in developing countries, where it is increasingly recognized as a contributor to the morbidity and mortality of children. Currently, nitazoxanide is the only FDA-approved drug for the treatment of cryptosporidiosis. However, the efficacy of nitazoxanide is variable in immunocompetent patients, limited in children, and nonexistent in immunocompromised patients, indicating a pressing need for improved therapies.,