Manojit Pal

Medicinal chemistry approaches to the inhibition of dipeptidyl peptidase-4 for the treatment of type 2 diabetes

Emerging as an epidemic of the 21st century type 2 diabetes has become a major health problem throughout the globe. The number of deaths attributable to diabetes reflects the insufficient glycemic control achieved with the treatments used in recent past. DPP-4 inhibitors have been investigated as a new therapy with novel mechanisms of action and improved tolerability. DPP-4, a protease that specifically cleaves dipeptides from proteins and oligopeptides after a penultimate N-terminal proline or alanine, is involved in the degradation of a number of neuropeptides, peptide hormones and cytokines, including the incretins GLP-1 and GIP. As soon as released from the gut in response to food intake, GLP-1 and GIP exert a potent glucose-dependent insulinotropic action, thereby playing a key role in the maintenance of post-meal glycemic control. Consequently, inhibiting DPP-4 prolongs the action of GLP-1 and GIP, which in turn improves glucose homeostasis with a low risk of hypoglycemia and potential for disease modification. Indeed, clinical trials involving diabetic patients have shown improved glucose control by administering DPP-4 inhibitors, thus demonstrating the benefit of this promising new class of antidiabetics. Intense research activities in this area have resulted in the launch of sitagliptin and vildagliptin (in Europe only) and the advancement of a few others into preregistration/phase 3, for example, saxagliptin, alogliptin and ABT-279. Achieving desired selectivity for DPP-4 over other related peptidases such as DPP-8 and DPP-9 (inhibition of which was linked to toxicity in animal studies) and long-acting potential for maximal efficacy (particularly in more severe diabetic patients) were the major challenges. Whether these goals are achieved with the present series of inhibitors in the advanced stages of clinical development is yet to be confirmed. Nevertheless, treatment of this metabolic disorder especially in the early stages of the disease via DPP-4 inhibition has been recognized as a validated principle and a large number of inhibitors are presently in various stage of pre-clinical/clinical development. Sitagliptin is a new weapon in the arsenal of oral antihyperglycemic agents. This review will focus on the journey of drug discovery of DPP-4 inhibitors for oral delivery covering a brief scientific background and medicinal chemistry approaches along with the status of advanced clinical candidates.

Isocoumarin and Its Derivatives: An Overview on their Synthesis and Applications

The prevalence of isocoumarins in numerous natural products that exhibit a wide range of biological activities has generated a continued and enormous interest among synthetic and medicinal chemists. The isocoumarin framework represents one of the privileged structures for the development of natural product-inspired compounds of potential biological interest. Considerable efforts have been de- voted towards the synthesis of isocoumarins via either traditional or transition-metal catalyzed reactions. Among the metal catalyzed re- actions, the use of Cu, Pd, Ag, Ru, Rh or Ir salts/complexes for the construction of isocoumarin ring are noteworthy. Among the other methodologies, halo-lactonization emerged as a practical process. Apart from preparing a variety of isocoumarins and thienopyranones, synthesis of naturally occurring and bioactive isocoumarins have been carried out by using cutting edge technologies. This review article will briefly cover all these aspects along with the synthetic utility of isocoumarins, highlighting recent developments.

Emerging drug candidates of dipeptidyl peptidase IV (DPP IV) inhibitor class for the treatment of Type 2 Diabetes.

Dipeptidyl peptidase IV (DPP IV) is a key regulator of insulin-stimulating hormones, glucagon-like peptide (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), thus it is a promising target for the treatment of Type 2 Diabetes mellitus (T2DM). Inhibition of plasma DPP IV enzyme leads to enhanced endogenous GLP-1 and GIP activity, which ultimately results in the potentiation of insulin secretion by pancreatic beta-cells and subsequent lowering of blood glucose levels, HbA[1(c)], glucagon secretion and liver glucose production. Various classes of structurally different DPP IV inhibitors are currently being explored and few of them such as Sitagliptin and Vildagliptin were successfully launched. These drugs have been approved as a once-daily oral monotherapy or as a combination therapy with current anti-diabetic agents like pioglitazone, glibenclamide, metformin etc. for the treatment of T2DM. Several other novel DPP IV inhibitors are in pipeline. The present review summarizes the latest preclinical and clinical trial data of different DPP IV inhibitors with a special emphasis on their DPP8/9 fold selectivity and therapeutic advantages over GLP-1 based approach.

Recent advances in glucokinase activators for the treatment of type 2 diabetes

Glucokinase is a member of the hexokinase family of enzymes that are responsible for the phosphorylation of glucose to glucose-6-phosphate for further utilization in cells. The enzyme plays a key role in glucose homeostasis. Phosphorylation of glucose by glucokinase in the liver promotes glycogen synthesis, while in the beta-cell it results in insulin release. Activators of glucokinase increase the sensitivity of the enzyme to glucose, leading to increased insulin secretion and liver glycogen synthesis and a decrease in liver glucose output. Thus, small molecule glucokinase activators have been demonstrated to be effective glucose-lowering agents in animal models of type 2 diabetes and have advanced into clinical studies.

Catalysis by molecular iodine: a rapid synthesis of 1,8-dioxo-octahydroxanthenes and their evaluation as potential anticancer agents.

Molecular iodine facilitated the reaction of 5,5-dimethyl-1,3-cyclohexanedione with aromatic aldehydes in iso-propanol affording a variety of 1,8-dioxo-octahydroxanthenes in high yields. Most of the compounds synthesized showed good anti-proliferative properties in vitro against three cancer cell lines and 9-(2-hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione possessing a 2-hydroxy phenyl group at C-9 position was found to be promising. Further structure elaboration of the same compound and the crystal structure analysis and hydrogen bonding patterns of another compound that is, 9-(4-methoxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione prepared by using this methodology is presented.

Pd-mediated new synthesis of pyrroles: their evaluation as potential inhibitors of phosphodiesterase 4

A sequential Pd-mediated multi-component reaction followed by Suzuki or Heck or Sonogashira coupling in a single pot has been developed for the synthesis of functionalized pyrroles as potential inhibitors of PDE4.

Iodine catalyzed four-component reaction: a straightforward one-pot synthesis of functionalized pyrroles under metal-free conditions

An iodine-catalyzed four-component reaction of 1,3-dicarbonyl compounds, amines, aldehydes and nitroalkanes afforded polysubstituted pyrroles under a metal free condition. Simplicity, low cost and good yields are the key features of this methodology. The mechanism of this four component process is discussed and structural elaboration of one of the compounds synthesized using Suzuki and Sonogashira coupling is presented.

Synthesis and evaluation of 3-amino/guanidine substituted phenyl oxazoles as a novel class of LSD1 inhibitors with anti-proliferative properties

A series of functionalized phenyl oxazole derivatives was designed, synthesized and screened in vitro for their activities against LSD1 and for effects on viability of cervical and breast cancer cells, and in vivo for effects using zebrafish embryos. These compounds are likely to act via multiple epigenetic mechanisms specific to cancer cells including LSD1 inhibition.

Quinolines: a new hope against inflammation.

Although a number of anti-inflammatory drugs have been discovered and developed to treat diseases associated with acute and chronic inflammation, many anti-inflammatories cause adverse side effects. The quinoline framework has emerged as a new template for the design and identification of novel anti-inflammatory agents. These agents are classified based on the number of substituents present on the quinoline ring or compounds containing a quinoline ring fused to other heterocycles. This review focuses on the discovery of various quinoline derivatives as inhibitors of cyclooxygenase (COX), phosphodiesterase 4 (PDE4) and tumour necrosis factor-α converting enzyme (TACE), along with transient receptor potential vanilloid 1 (TRPV1) antagonists.

Novel N-indolylmethyl substituted olanzapine derivatives: their design, synthesis and evaluation as PDE4B inhibitors

A new strategy for converting antipsychotic drug olanzapine into PDE4 inhibitors is described via the design and Pd/C mediated synthesis of novel N-indolylmethyl olanzapine derivatives. One compound showed good inhibition (IC50 1.1 μM) and >10 fold selectivity towards PDE4B over D that was supported by docking studies. This compound also showed significant inhibition of TNF-α and no major toxicities in cell lines and a zebrafish embryo model except the teratogenic effects to be re-assessed in rodents.