In the year 1955, a water-soluble hydroxyl-containing chloroquine derivative as hydroxychloroquine (HCQ; 1) was approved by US FDA for the treatment of malarial fever (Figure ). It is a racemic mixture consisting of an (R) and (S) enantiomer, and currently sold under the brand name of Plaquenil®, Hydroquin®, Axemal®, Dolquine®, Quensyl®, Quinoric®, etc. as a therapeutics for malaria, rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), and primary Sjögren syndrome. Currently, it is one of the frequently prescribed drugs across the USA, and included in the World Health Organization's List of Essential Medicines.