Organocatalytic Enantiospecific Total Synthesis of Butenolides

Two-step, high-yielding total synthesis of antibiotic pyrones

A simple two-step dialkylation protocol was developed to synthesize biologically active antibiotics photopyrones, pseudopyronines, and violapyrones from bio-renewable triacetate lactone in excellent yields. These pyrones are functionally modified into another set of pyrone natural products by a single O-methylation reaction. The high-yielding gram scale synthesis of four natural products [pseudopyronine A, photopyrone A, pseudopyronine B and photopyrone C] demonstrated the viability for industrial applications.

Electron-Poor Butenolides: The Missing Link between Acrylates and Maleic Anhydride in Radical Polymerization

Butenolides are a class of 5-membered lactones that hold great potential as bio-based monomers to replace oil-derived acrylates, of which they are cyclic analogues. Despite this structural resemblance, the reactivity of the unsaturated ester moiety of electron-poor butenolides leans toward that of maleic anhydride, another essential monomer that does not homopolymerize but copolymerizes in a highly alternating fashion with polarized electron-rich comonomers. By studying the reactivity of 5-methoxy and 5-acyloxy butenolides through a combination of kinetics and density functional theory (DFT) experiments, we explain why electron-poor butenolides constitute a missing link between acrylates and maleic anhydride in radical polymerization.

Synthetic drives for useful drug molecules through organocatalytic methods

The treatment of various pathological conditions in human beings involves the use of safe and efficacious drug substances. But there are different complications associated with the treatment of various disease states including drug resistance, adverse drug reactions, toxicity, etc. To minimize these problems, there is an urgent need to develop new therapeutics with suitable pharmacokinetic and pharmacodynamic properties. So, the organocatalytic methods are emerged as a potential synthetic tool to accelerate the design of new drug candidates with improved physicochemical and pharmacological properties, selectivity, and efficiency for the treatment of life-threatening diseases. Organocatalytic reactions refer to the chemical reaction that is accelerated by organic catalysts instead of using organometallic catalysts. Organocatalysts are more advantageous in comparison to metallic catalysts because organocatalysts are cost-effective, stable, efficient, non-toxic, readily available, and easy to handle. In addition to this, the organocatalysis method involves an eco-friendly reaction by minimizing the formation of by-products and reducing the chemical hazards. Organocatalysts are categorized into four classes such as Lewis acids, Lewis bases, Bronsted acids, and Bronsted bases. These catalysts are generally involved in various reactions mechanisms such as Aldol reaction, Diels–Alder reactions, Michael Addition and Knoevenagal reactions, etc. The utility of organocatalyst in synthetic chemistry results in the development of medicinally active compounds with diverse structural features.

Organocatalysts based on natural and modified amino acids for asymmetric reactions

Small organic molecules predominantly containing C, H, O, N, S and P element are found promising molecule to accelerate chemical reactions and are named organocatalysis. In addition, these organocatalysts are easy availability, stable in water and air, inexpensive, and low toxicity, which confer a huge direct application in organic synthesis when compared to transition metal catalyzed reactions and becoming powerful tools in the construction of a selective chiral product. Interest on organocatalysis is spectacularly increased since last two decades, due to the novelty of the concept and selectivity. Based on the nature of the organocatalysts used, they are classified in to four major classes, among them one of the types is amino acids derived organocatalysts. Natural amino acids are playing important role in building blocks of protein construction, and also intermediate products of the metabolism. α-Amino acid is a molecule, that contains both amine and carboxyl functional group. Their particular structural characteristic determines their role in protein synthesis, and bifunctional asymmetric catalysts for stereoselective synthesis. Two functional groups present on a single carbon acting as an acid and base, which promote chemical transformations in concert similar to the enzymatic catalysis. The post translational derivatives of natural α-amino acids include 4-hydroxy-L-proline and 4-amino-L-proline scaffolds, and its synthetic variants based organocatalysts, whose catalytic activity is well documented. This chapter discussed past and present development of the organocatalysts derived from natural and modified amino acids for various important organic transformations reviewed.