Synthetic versus Enzymatic Pictet-Spengler Reaction: An Overview

Background: Pictet-Spengler reactions is an irreplaceable part of cyclization reaction leading to the formation of indispensable heterocyclic moieties including imidazole, benzoxazole, pyrrole, indole and others having immense biological and chemical significance. Researchers have explored this reaction using different types of catalysts and reactions conditions (including solvents, acids, etc.) to ensure the better selectivity, less reaction time and high product yields. A total of five Pictet-Spenglerases have been discovered from various sources including plants, animals, fungi, and microbes, and are responsible for the synthesis of various important alkaloids of biological medicinal importance. Objective: The present review is a strenuous effort to assemble information mainly focusing on synthetic as well as biological Pictet-Spengler reactions catalysed by enzymes called Pictet-Spenglerase. Conclusion: In the present review, the recent advances in the PS-mediated synthesis of diverse heterocycles such as tetrahydroisoquinoline, tetrahydro-beta-carbolines, tetrahydroimidazopyridines and other fused heterocycles via chemical as well as enzymatic pathways have been covered. The compounds find their scope as medicinal agents for the treatment of cancer, tuberculosis, bacterial infection, leishmanial, etc. The compilation is expected to provide a mechanistic insight to chemists to enhance the reaction condition, yields and another parameter to ensure the safe and inexpensive reaction conditions considering the "Green-Concept" of chemistry.