Lewis acid mediated highly regioselective intramolecular cyclization for the synthesis of β-lapachone

Beta-lapachone: Natural occurrence, physicochemical properties, biological activities, toxicity and synthesis

β-Lapachone is an ortho-naphthoquinone originally isolated from the heartwood of Handroanthus impetiginosus and can be obtained through synthesis from lapachol, naphthoquinones, and other aromatic compounds. β-Lapachone is well known to inhibit topoisomerase I and to induce NAD(P)H: quinone oxidoreductase 1. Currently, phase II clinical trials are being conducted for the treatment of pancreatic cancer. In view of ever-increasing scientific interest in this naphthoquinone, herein, the authors present a review of the synthesis, physicochemical properties, biological activities, and toxicity of β-lapachone. This natural compound has shown activity against several types of malignant tumors, such as lung and pancreatic cancers and melanoma. Furthermore, this ortho-naphthoquinone has antifungal and antibacterial activities, underscoring its action against resistant microorganisms and providing anti-inflammatory, antiobesity, antioxidant, neuroprotective, nephroprotective, and wound-healing properties. β-Lapachone presents low toxicity, with no signs of toxicity against alveolar macrophages, dermal fibroblast cells, hepatocytes, or kidney cells.

α- and β-Lapachone Isomerization in Acidic Media: Insights from Experimental and Implicit/Explicit Solvation Approaches

Combined experimental and mixed implicit/explicit solvation approaches were employed to gain insights into the origin of switchable regioselectivity of acid-catalyzed lapachol cyclization and α-/β-lapachone isomerization. It was found that solvating species under distinct experimental conditions stabilized α- and β-lapachone differently, thus altering the identity of the thermodynamic product. The energy profile for lapachol cyclization revealed that this process can occur with low free-energy barriers (lower than 8.0 kcal mol^-1 ). For α/β isomerization in a dilute medium, the computed enthalpic barriers are 15.1 kcal mol^-1 (α→β) and 14.2 kcal mol^-1 (β→α). These barriers are lowered in concentrated medium to 11.5 and 12.6 kcal mol^-1 , respectively. Experimental determination of isomers ratio was quantified by HPLC and NMR measurements. These findings provide insights into the chemical behavior of lapachol and lapachone derivatives in more complex environments.

An efficient cyclization of lapachol to new benzo[h]chromene hybrid compounds: a stepwisevs.one-pot esterification-click (CuAAC) study

Comparison of one-potvs.stepwise esterification of lapachol to obtain highly diversified heterocycles. Whereas the one-pot esterification leads to mono esterified lapachol, the tandem approach generated benzo[h]chromene.

Niobium-Catalyzed Intramolecular Addition of O-H and N-H Bonds to Alkenes: A Tool for Hydrofunctionalization

A convenient, versatile, and easy to handle intramolecular hydrofunctionalization of alkenes (C-O and C-N bonds formation) is reported using a novel niobium-based catalytic system. This atom economic and eco-friendly methodology provides an additional synthetic tool for the straightforward formation of valuable building blocks enabling molecular complexity. Various pyran, furan, pyrrolidine, piperidine, lactone, and lactam derivatives as well as spirocyclic compounds are produced in high yields and selectivities.

Novel naphthoquinone derivatives and evaluation of their trypanocidal and leishmanicidal activities

Novel naphthoquinone derivatives were synthesized and tested for trypanocidal and leishmanicidal activities. Compound 11a was the most active against T. cruzi.