Synthetically or naturally available naphthoquinones with a hydroxyl group on quinone moieties are known as lawsone and its isomeric forms are responsible for biological and structural properties. Among several naphthoquinones, lawsone is the simplest form of naturally occurring naphthoquinone. Lawsone is naturally obtained from the Henna (Gorintaku) plant leaves, which is responsible for the red-orange pigment properties. Henna extracts are used as a traditional coloring agent for skin, hair, nails, and clothes for more than 5000 years. The Henna extract is also used in various platforms like pharmaceutical, cosmetic, and cloth dyeing. It acts as an anti-aging additive to vulcanized natural rubber, oxidation of chlorinated compounds, corrosion inhibition for steel, etc. The red-dye pigmentation properties of Henna are due to the chemical reaction of lawsone with keratin protein. Lawsone undergoes dehydrative Michael reaction with the keratin protein in skin, hair, and nails, which results in a dark stain to the hair, skin and nails. The darker colored ink is due to more lawsone-keratin interactions occurring, which evidently break down as the concentration of lawsone decreases and the tattoo fades.
The catalysis laboratory @ School of Chemistry mainly focuses on the reaction development for the synthesis of biologically important molecules in one-pot manner. In a search of suitable green reactants, we found lawsone as suitable starting material for the discovery of new organocatalytic asymmetric reactions. In 2010, our first investigation on lawsone was reported for catalytic reductive alkylation (Org. Biomol. Chem. 2010, 8, 2859-2867), later it become important for many chemists/biologists. In 2017, we reported the organocatalytic asymmetric formal [3+2]-cycloaddition as a versatile platform to access biologically important methanobenzoannulenes from the lawsones (Angew. Chem. Int. Ed. 2017, 56, 12930-12934). In 2019, we reported the catalytic synthesis of biologically important benzannulated bicyclo[3.3.0]octanes, methanodibenzo[a,f]azulenes and methanobenzo[f]azulenes from the lawsones (Chem. Eur. J. 2019, 25, 1177-1183, and Chem. Eur. J. 2019, 25, 14036-14041). In 2019, we reported the organocatalytic reductive propargylation on lawsones, which is an unsolved problem over decades (J. Org. Chem. 2019, 84, 15399-15416).
All these important new organocatalytic reactions presented thoroughly with complete discussions in the PhD thesis submitted by Dr. Mohammad Anif Pasha under the supervision of Prof. Dr. Dhevalapally B. Ramachary at the School of Chemistry, UoH. Same time Prof. D. B. Ramachary acknowledge the extensive contributions of Dr. G. Thirupathi, Dr. A. Suresh Kumar and Dr. Swamy Perakaas as a postdoctoral fellows to develop lawsone as suitable synthon for the discovery of organocatalytic reactions.
Dr. Mohd Anif Pasha Dr. G. Thirupathi Dr. A. Suresh Kumar Dr. Swamy Peraka
These colorful catalytic reactions surely will add more color to the lawsone !!!