Efficient and Clean Synthesis of 1,8-Dioxooctahydroxanthenes in Aqueous Medium

Abstract

INTRODUCTION Xanthenes have attracted a number of research efforts in synthetic organic chemistry due to their wide range of biological and pharmacological properties like antiviral [1], antibacterial [2] and anti-inflammatory activities [3], as well as in photodynamic therapy [4] and as antagonists of the paralyzing action of zoxazolamine [5]. Xanthenes are also available from many natural sources. The prominent among them are dibenzoxanthenes, hexahydroxanthene and octahydroxanthene. Xanthenes are frequently occurring motifs in a number of natural products [6] and have been used as versatile synthons due to the inherent reactivity of inbuilt pyran ring [7]. Octahydroxanthene derivatives containing a structural unit of benzopyrans can be used as antispasm agents [8] and fluorescent fuel [9]. Furthermore, due to their useful spectroscopic properties, they are used as dyes and pigments [10,11], in laser technologies [12] and in fluorescent materials for visualization of biomolecules [13]. Xanthenes are also known to possess many pharmacological properties. Allanxanthone C, a xanthene derivative obtained from Allanblackia monticola exhibits excellent biological properties [14]. Ehretianone, a quinonoid xanthene obtained from Ehretia buxifolia is reported to possess anti-snake venom activity [15]. A spiro-compound of xanthene, xanthene spiropiperidine, is well-known as a sedative and antihistaminic agent