A simple and green method for the synthesis of aurones by condensation of benzofuranone with aromatic aldehyde in neat water has been developed. The main advantages of this protocol include good yields, absence of catalyst, reagent, organic solvent, work-up and chromatographic purification. 4,5,3',4',5'-Pentamethoxy-6-hydroxyaurone, isolated from Smilax riparia was synthesized for the first time from 3-benzyloxy-4,5-dimethoxybenzaldehyde in five steps.
A novel series of aurones were designed by introducing sulfonic acid group on ring-A and ring-B of known natural aurones such as hispidol, sulfuretin, maritimetin, and aureusidin. These sulfonated aurones were synthesized by a unique approach. Sulfonation on ring-A or ring-B converts water-insoluble aurones into highly water-soluble aurones. The sulfonated aurones were tested for their antioxidant, antiinflammatory, and AChE inhibition activities along with their natural aurones. Ring-A sulfonated aurones displayed higher antioxidant activity, 5-LOX, and AChE inhibition in comparison with their corresponding natural aurones. Ring-B sulfonated aurones exhibited potent 5-LOX inhibitory activity and significant antioxidant activity. Acidoaurone, a first sulfonated aurone isolated from Phyllanthus acidus was synthesized for the first time and was well characterized using NMR, LC-MS, and further confirmed by HMBC.
To widen aurones applicability in achromatic food and cosmetic applications, a series of dihydroaurones
were designed to mimic natural aurones as well as synthetic aurones. Dihydroaurones have been
synthesized from the corresponding aurones by hydrogenation. These dihydroaurones and their
corresponding aurones were screened for antioxidant, anti-inflammatory and tyrosinase enzyme
inhibitory activity. Synthesized dihydroaurones (3b-f) displayed superior antioxidant activity in
superoxide free radical scavenging assay than the standard gallic acid. Dihydroaurones (3b-f) also
exhibited significant tyrosinase enzyme inhibitory activity and two dihydroaurones (3h, 3j) showed
promising 5-lipoxygenase inhibitory activity.
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