J. Indian Chern. Soc., Vol. 85, March 2008, pp. 310-312 Tabebuin and tecomaquinone-111-dimeric quinones from Tabebuia rosea Poonam Khandelwal and Pahup Singh* Centre of Advanced Studies, Department of Chemistry, University of Rajasthan, Jaipur-302 004, Rajasthan, India E-mail : pahupsingh@yahoo.co.uk Manuscript received 1 August 2007, revised 30 November 2007, accepted 30 November 2007 Abstract : Two dimeric C 311 quinoncs-tabebuin and tecomaquinone-111 have been isolated from the heartwood of Tabebuia rosea in addition to the previously reported 1,4-naphthoquinonc derivatives. Both the dimcric quinones arc reported for the first time from this plant. Keywords : Tabebuin, tecomaquinone-111, Tabebuia rosea, Bignoniaceac. Introduction Continuing our study on coloured pigments from the heartwoods of various Bignoniaceae 1 , we re-examined the heartwood of Tabebuia rosea DC. (Bignoniaceae). It is an ornamental tree with multiannular masses of light pink tlowers and belongs to typical tropical and sub tropical areas. It is a native of Brazil. Its roots is prescribed as drink in scorpion-sting and its wood-tar has been used in various skin diseases 2 . Previous work on this plant included the isolation of several C 15 naphthoquinone congeners related to lapachol ,and a dimeric c30 quinone, tecomaquinone-I from the heartwood 3 , bark 4 and roots 5 . P-Lapachone one of its constituents displayed a potent inhibitor of transcri ptase activity from myeloblastosis virus and Rauscher murine leukemia virus. In addition, it affects eukaryotic DNA-dependent DNA-polymerase activity 6 . Several naphthoquinones including diosquinone and trimeric naphthoquinone derivative conocurvone have shown cytotoxic and anti-HlV activities 7 - 9 . An antimicrobial naphthoquinone pigment, cribrarione, was isolated from Cribraria purpurea 10 . In this paper, we now report the isolation and characterization of tabebuin (1) and tecomaquinone-III (2) as dimeric quinones from the heartwood of Tabebuia rosea. Both of these pigments are reported second time from the nature and first time from T. rosea. Earlier tabebuin (1) was reported from T. avellanedae 11 and tecomaquinone-III (2) was isolated from T. pentaphylla 12 . Numbering in compounds (1) and (2) is arbitrary and is done for indicating 13 C chemical shift of various carbon atoms. 310 0 (1) 2 s· (2) Results and discussion Tabebuin (1) was obtained as pale orange needles, m.p. 211-212° and has molecular formula C 31 H 26 0 5 , [Mj+ 478. It contains one methoxy (3.92 ppm), one aromatic methyl (1.68 ppm) and two gem-dimethyl groups (1.82 and 1.84 ppm). Methylene protons of pyran ring appear as a pair of double doublets (2.35 and 2.43 ppm) which couple with a methine proton (dd) under oxygen function (4.88 ppm). Aromatic protons exhibit signals in the region 6.46 to 8.22 ppm. The 13 C NMR spectrum displayed 31 carbon signals, among which four are methyls, one is methylene, twelve are methine and fourteen are quaternary carbon atoms. Nature of various carbon atoms was ascertained by DEPT 135 experiment. Tabebuin shows a strong quinone