Reflexin in Selective Sensing of NO 63 Applied Biochemistry and Biotechnology Vol. 127, 2005 Copyright © 2005 by Humana Press Inc. All rights of any nature whatsoever reserved. 0273-2289/05/127/0063/$30.00 63 *Author to whom all correspondence and reprint requests should be addressed. A New Flavanone, Reflexin, From Cuscuta reflexa and Its Selective Sensing of Nitric Oxide V. J. TRIPATHI,* S. B. YADAV, AND A. K. UPADHYAY Department of Chemistry, Banaras Hindu University, Varanasi-221 005, India, E-mail: sbyadavbhu@rediffmail.com Received September 6, 2004; Accepted March 23, 2005 Abstract A new compound, reflexin, 5-hydroxy-7-methoxy-6-(2,3-epoxy-3-methyl- butyl)-flavanone, is isolated from the stems of Cuscuta reflexa along with three other known compounds. This new compound has good potential for application especially in the photoactivity of reflexin. It was found to be sensitive to glutathione, forming a fluorescent product that is utilized for sensing nitric oxide (NO). The lowest detection limit of NO analysis was found to be 0.05 μM. Index Entries: Reflexin; nitric oxide; Cuscuta reflexa; glutathione; nitro- sothiol. Introduction In a continuation of our chemical investigation (1,2) of Cuscuta reflexa, Roxb. (family: Convolvulaceae), a time-honored drug in the Indian system of medicine (3,4), in this article we report on the isolation, characterization, and study of the biological properties of a new flavonoid, reflexin, designated as Fig. 1 along with other known compounds, namely (5–7) apigenin-7-o-glucoside, kaempferol-3-o-α-rhamnoside, and myricetin-3-o- α-rhamnoside. Several of such compounds are highly photochromic in nature, which led us to investigate whether such compounds could be of use in technological applications based on the measurement of photo- activity. The detection of nitric oxide (NO) is important for human health because NO is involved in various biological processes such as brain ischemia, neurotransmission, immune regulation, and penile erection (8–11)