TERPENOIDS-LX11. The constitution of Agarospirol, a Sesquiterpenoid with a new skeleton

Abstract

Abtract-Degradative studies and physical measurements supported by an unambiguous synthesis of the derived ketone (XVa) have led to the assignment of a novel Spiro-skeleton to agarospirol (Ia), a sesquiterpene alcohol isolated from the essential oil of infected agarwood (Aquihria t@~ocha Roxb.). The corresponding carbon skeleton (VI) has been named agarospirane. Agarospirol is the second Spiro-terpenoid to be isolated from Nature. The most probable stereochemistry of agaro-Spiro1 appears to be as in XxX1X. WORK from this Laboratory on the constituents of agarwood oilt (Aquilaria agollocha Roxb.) has been recorded in previous papers. l--I Investigations of the alcoholic con-stituents has led to the isolation of a new monoethenoid, bicyclic, sesquiterpene alco-hol, C,,H,O, as a major component. Chemical and spectroscopic studies supported by the synthesis of one of the derived ketones (XVa) indicates that this alcohol pos-sesses a novel Spiro-bicyclodecane structure (Ia). It is the second Spiro-terpenoid to be isolated from Nature, the first, acorone @VIII), was isolated from the oil of sweet flag (Acorns culamus Linn.) and studied6 by Sorm et al. We propose to name this alcohol agarospirol and the corresponding carbon skeleton (VI) agar0spirane.t Agarospirol was isolated as such in the pure state (GLC) free from other related constituents by column chromatography, or preferably, as the acetate, which forms only under energetic conditions (NaOAc-Ac,O,). The acetate, C,,H,OB (Ib), on saponification with cold alcoholic potash gives pure agarospirol, &HMO (ia), which may be reconverted to the same acetate. The acetate is resistant to LAH in refluxing tetrahydrofuran. Agarospirol, CIBHMO (la), (a)g -57 " , an oil, b.p. 9O-91 " /0*1 mm, Y,_ 3472, 1149 cm-l (t-OH), does not give a solid ester derivative, but a crystalline monoepox-ide, C,H,O* (II), m.p. 109-l 10 " ; the presence of another liquid epimeric epoxide l Communication No. 715 from the National Chemical Laboratory, Poona-8, India. t The oil studied was obtained by solvent extraction from the infected wood. $ The numbering of the carbon skeleton is analogous with that of acorone (XVIII) and does not follow the I.U.P.A.C. Rule, J. Amer. C&m. Sot. 82, 5545 (1960).