Insulin sensitizers in 2023: lessons learned and new avenues for investigation

INTRODUCTION

'Insulin sensitizers' derived discoveries of the Takeda Company in 1970s. Pioglitazone remains the best in class with beneficial pleiotropic pharmacology, although use is limited by tolerability issues. Various attempts to expand out of this class assumed the primary molecular target was the transcription factor, PPARγ. Findings over the last 10 years have identified new targets of thiazolidinediones (TZDs) that should alter the drug discovery paradigm.

AREAS COVERED

We review structural classes of experimental insulin sensitizer drugs, some of which have attained limited approval in some markets. The TZD pioglitazone, originally approved in 1999 as a secondary treatment for type 2 diabetes, has demonstrated benefit in apparently diverse spectrums of disease from cardiovascular to neurological issues. New TZDs modulate a newly identified mitochondrial target (the mitochondrial pyruvate carrier) to reprogram metabolism and produce insulin sensitizing pharmacology devoid of tolerability issues.

EXPERT OPINION

Greater understanding of the mechanism of action of insulin sensitizing drugs can expand the rationale for the fields of treatment and potential for treatment combinations. This understanding can facilitate the registration and broader use of agents with that impact the pathophysiology that underlies chronic metabolic diseases as well as host responses to environmental insults including pathogens, insulin sensitizer, MPC, mitochondrial target, metabolic reprogramming, chronic and infectious disease.

Oxidative α-Functionalization of 1,2,3,4-Tetrahydroisoquinolines Catalyzed by a Magnetically Recoverable Copper Nanocatalyst. Application in the Aza-Henry Reaction and the Synthesis of 3,4-Dihydroisoquinolones

The oxidative α-functionalization of 2-aryl-1,2,3,4-tetrahydroisoquinolines (THIQs) promoted by a versatile heterogeneous nanocatalyst consisting of copper nanoparticles immobilized on silica-coated maghemite (CuNPs/MagSilica) has been accomplished. The methodology was successfully applied in the cross-dehydrogenative coupling (CDC) reaction of N-aryl THIQs and other tertiary amines with nitromethane as a pro-nucleophile (aza-Henry reaction) and the α-oxidation of THIQs with O₂ as a green oxidant. Phosphite, alkyne, or indole derivatives were also shown to be suitable candidates for their use as pro-nucleophiles in the CDC reaction with THIQs. The catalyst, with very low copper loading (0.4-1.0 mol % Cu), could be easily recovered by means of an external magnet and reused in four cycles without significant loss of activity.

Synthesis and Evaluation of a Novel Series of 2,7-Substituted-6-tetrazolyl-1,2,3,4-tetrahydroisoquinoline Derivatives as Selective Peroxisome Proliferator-Activated Receptor γ Partial Agonists

A novel series of 7-substituted-2-[3-(2-furyl)acryloyl]-6-tetrazolyl-1,2,3,4-tetrahydroisoquinoline derivatives were synthesized to clarify structure-activity relationships for peroxisome proliferator-activated receptor γ (PPARγ) partial agonist activity and identify more efficacious PPARγ partial agonists with minor adverse effects. Among the derivatives synthesized, compound 26v with a 2-(2,5-dihydropyrrol-1-yl)-5-methyloxazol-4-ylmethoxy group at the 7-position of the tetrahydroisoquinoline structure exhibited stronger PPARγ agonist and antagonist activities (EC50 = 6 nM and IC50 = 101 nM) than previously reported values for compound 1 (EC50 = 13 nM and IC50 = 512 nM). Compound 26v had very weak protein tyrosine phosphatase 1B (PTP1B) inhibitory activity and showed higher oral absorption (Cmax = 11.4 µg/mL and area under the curve (AUC) = 134.7 µg·h/mL) than compound 1 (Cmax = 7.0 µg/mL and AUC = 63.9 µg·h/mL) in male Sprague-Dawley (SD) rats. A computational docking calculation revealed that 26v bound to PPARγ in a similar manner to that of compound 1. In male Zucker fatty rats, 26v and pioglitazone at 10 and 30 mg/kg for 4 weeks similarly reduced plasma triglyceride levels, increased plasma adiponectin levels, and attenuated increases in plasma glucose levels in the oral glucose tolerance test, while only pioglitazone decreased hematocrit values. In conclusion, 6-tetrazolyl-1,2,3,4-tetrahydroisoquinoline derivatives provide a novel scaffold for selective PPARγ partial agonists and 26v attenuates insulin resistance possibly by adiponectin enhancements with minor adverse effects.

(S)-1,2,3,4-Tetrahydroisoquinoline Derivatives Substituted with an Acidic Group at the 6-Position as a Selective Peroxisome Proliferator-Activated Receptor γ Partial Agonist

A novel series of 2,6,7-substituted 3-unsubstituted 1,2,3,4-tetrahydroisoquinoline derivatives were synthesized to find a peroxisome proliferator-activated receptor γ (PPARγ) partial agonist. Among the derivatives, (E)-7-[2-(cyclopent-3-eny)-5-methyloxazol-4-ylmethoxy]-2-[3-(2-furyl)acryloyl]-6-(1H-tetrazol-5-yl)-1,2,3,4-tetrahydroisoquinoline (20g) exhibited potent partial agonist activity (EC₅₀ = 13 nM, maximal response 30%) and very weak protein tyrosine phosphatase 1B (PTP1B) inhibition (IC₅₀ = 1100 nM), indicating a selective PPARγ partial agonist. A computational docking calculation revealed that 20g bound to PPARγ in a similar manner to that of known partial agonists. In male and female KK-A^y mice with insulin resistance and hyperglycemia, 20g at 30 mg/kg for 7 d significantly reduced plasma glucose levels, but not triglyceride levels. The effects of 20g were similar to those of pioglitazone at 10 mg/kg. In conclusion, the 2,6,7-substituted 1,2,3,4-tetrahydroisoquinoline with an acidic group at the 6-position provides a novel scaffold for selective PPARγ partial agonists and 20g exerted anti-diabetic effects via the partial activation of PPARγ.

Diversity-oriented synthesis of medicinally important 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) derivatives and higher analogs

1,2,3,4-Tetrahydroisoquinoline-3-carboxylic acid (Tic) is a constrained analog of phenylalanine (Phe). The Tic unit has been identified as a core structural element present in several peptide-based drugs and forms an integral part of various biologically active compounds. This report covers the biological significance of the Tic core and provides a detailed account of various synthetic approaches available for the construction of Tic derivatives. Along with the traditional methods such as the Pictet-Spengler and Bischler-Nepieralski reactions, we cover various recent approaches such as enyne metathesis, [2 + 2 + 2] cycloaddition and the Diels-Alder reaction to generate Tic derivatives. In addition, syntheses of higher analogs of Tic are also discussed.

Chemopreventive effect of Lagenaria siceraria in two stages DMBA plus croton oil induced skin papillomagenesis

Cancer chemoprevention is a dietary or therapeutic strategy to prevent, suppress, or delay carcinogenesis either at initiation or progression level with nontoxic agents. Use of natural dietary compounds has been a major chemopreventive approach to modulate tumorigenic pathways. In the present study, we have evaluated Lagenaria siceraria (bottle gourd), a common vegetable of Indian household for its chemomodulatory potential. The fruit has been used in traditional medicine for a very long time for health benefits and to cure pain, ulcers, fever, cough, asthma, and other bronchial disorders. However, despite its reported beneficial effect the chemo modulatory potential of this plant has not been reported. Therefore chemopreventive effect of bottle gourd juice (BGJ) was studied against 7,12-dimethylbenz(a)anthracene (DMBA) plus croton oil induced skin papillomagenesis in Swiss albino mice. The effect was studied both at antiinitiation and antiinitiation/promotion level followed by histopathological study. A dose of 2.5% and 5% given in drinking water showed significant decrease in papilloma number, papilloma incidence, papilloma multiplicity, papilloma latency, papilloma volume, and papilloma size in different size range. Histopathological study showed chemopreventive effect by minimizing loss of stratification, a decrease in number of epithelial layers, reducing dermal infiltration and protection for various cytoplasmic changes. Higher dose of BGJ was found to be more effective than lower dose and the chemopreventive effect was maximum for antiinitiation/promotion treatment. Altogether, this study reports the chemopreventive effect of Lagenaria siceraria on skin papillomagenesis for the first time and suggests that its consumption may help in suppression of skin cancer.

A novel series of (S)-2,7-substituted-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acids: peroxisome proliferator-activated receptor α/γ dual agonists with protein-tyrosine phosphatase 1B inhibitory activity

Novel 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives were synthesized and (S)-7-(2-{2-[(E)-2-cyclopentylvinyl]-5-methyloxazol-4-yl}ethoxy)-2-[(2E,4E)-hexadienoyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (14c) was identified as a peroxisome proliferator-activated receptor (PPAR) α/γ dual agonist. The transactivation activity of 14c was comparable to that of rosiglitazone in human PPARγ (EC50=0.14 µM) and was much higher than in human PPARα (EC50=0.20 µM). In addition, 14c, but not rosiglitazone, showed human protein-tyrosine phosphatase 1B (PTP-1B) inhibitory activity (IC50=1.85 µM). 14c showed about 10-fold stronger hypoglycemic and hypotriglyceridemic effects than rosiglitazone by repeated application for 14 d in male KK-Ay mice. Furthermore, 14c, but not rosiglitazone, increased hepatic peroxisome acyl CoA oxidase activity at 30 mg/kg/d for 7 d in male Syrian hamsters, probably due to its PPARα agonist activity. 14c did not affect plasma volume at 100 mg/kg/d for 14 d in male ICR mice, while rosiglitazone significantly increased it. In conclusion, 14c is a promising candidate for an efficacious and safe anti-diabetic drug with triple actions as a PPARα/γ dual agonist with PTP-1B inhibitory activity.

Potent direct inhibitors of factor Xa based on the tetrahydroisoquinoline scaffold

Direct inhibition of coagulation factor Xa (FXa) carries significant promise for developing effective and safe anticoagulants. Although a large number of FXa inhibitors have been studied, each can be classified as either possessing a highly flexible or a rigid core scaffold. We reasoned that an intermediate level of flexibility will provide high selectivity for FXa considering that its active site is less constrained in comparison to thrombin and more constrained as compared to trypsin. We studied several core scaffolds including 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid for direct FXa inhibition. Using a genetic algorithm-based docking and scoring approach, a promising candidate 23 was identified, synthesized, and found to inhibit FXa with a K(i) of 28 μM. Optimization of derivative 23 resulted in the design of a potent dicarboxamide 47, which displayed a K(i) of 135 nM. Dicarboxamide 47 displayed at least 1852-fold selectivity for FXa inhibition over other coagulation enzymes and doubled PT and aPTT of human plasma at 17.1 μM and 20.2 μM, respectively, which are comparable to those of clinically relevant agents. Dicarboxamide 47 is expected to serve as an excellent lead for further anticoagulant discovery.

Electronically Rich N-Substituted Tetrahydroisoquinoline 3-Carboxylic Acid Esters: Concise Synthesis and Conformational Studies

Recent work in our laboratory has shown that the highly substituted, electronically rich 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (THIQ3CA) scaffold is a key building block for a novel class of promising anticoagulants (Al-Horani et al. J. Med. Chem.2011, 54, 6125-6138). The synthesis of THIQ3CA analogs, especially containing specific, electronically rich substituents, has been a challenge and essentially no efficient methods have been reported in the literature. We describe three complementary, glycine donor-based strategies for high yielding synthesis of highly substituted, electronically rich THIQ3CA esters. Three glycine donors studied herein include hydantoin 1, (±)-Boc-α-phosphonoglycine trimethyl ester 2 and (±)-Z-α-phosphonoglycine trimethyl ester 3. Although the synthesis of THIQ3CA analogs could be achieved using either of the three, an optimal, high yielding approach for the desired THIQ3CA esters was best achieved using 3 in three mild, efficient steps. Using this approach, a focused library of advanced N-arylacyl, N-arylalkyl, and bis-THIQ3CA analogs was synthesized. Variable temperature and solvent-dependent NMR chemical shift studies indicated the presence of two major conformational rotamers in 3:1 proportion for N-arylacyl-THIQ3CA analogs, which were separated by a high kinetic barrier of ~17 kcal/mol. In contrast, N-arylalkyl and bis-THIQ3CA variants displayed no rotamerism, which implicates restricted rotation around the amide bond as the origin for high-barrier conformational interconversion. This phenomenon is of major significance because structure-based drug design typically utilizes only one conformation. Overall, the work presents fundamental studies on the synthesis and conformational properties of highly substituted, electronically rich THIQ3CA analogs.

Novel (S)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acids: peroxisome proliferator-activated receptor γ selective agonists with protein-tyrosine phosphatase 1B inhibition

A novel series of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives were synthesized and (S)-2-[(2E,4E)-hexadienoyl]-7-(2-{5-methyl-2-[(1E)-5-methylhexen-1-yl]oxazol-4-yl}ethoxy)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (14i) was identified as a potent human peroxisome proliferator-activated receptor γ (PPARγ) selective agonist (EC(50)=0.03 μM) and human protein-tyrosine phosphatase 1B (PTP-1B) inhibitor (IC(50)=1.18 μM). C(max) after oral administration of 14i at 10mg/kg was 2.2 μg/ml (4.5 μM) in male SD rats. Repeated administration of 14i and rosiglitazone for 14 days dose-dependently decreased plasma glucose levels, ED(50)=4.3 and 23 mg/kg/day, respectively, in male KK-A(y) mice. In female SD rats, repeated administration of 14i at 12.5-100mg/kg/day for 28 days had no effect on the hematocrit value (Ht) and red blood cell count (RBC), while rosiglitazone significantly decreased them from 25mg/kg/day. In conclusion, 14i showed about a fivefold stronger hypoglycemic effect and fourfold or more weaker hemodilution effect than rosiglitazone, indicating that 14i is 20-fold or more safer than rosiglitazone. Compound 14i is a promising candidate for an efficacious and safe anti-diabetic drug targeting PPARγ and PTP-1B.