MAGNETIC RESONANCE IN CHEMISTRY Magn. Reson. Chem. 37, 676–681 (1999) Note Two known bis-indole alkaloids isolated from Tabernaemontana laeta: complete 1 H and 13 C chemical shift assignments W. L. B. Medeiros, 1 I. J. C. Vieira, 2 L. Mathias, 2 R. Braz-Filho, 2 * K. Z. Leal, 3 E. Rodrigues-Filho 4 and J. Schripsema 2,5 1 Departamento de Qu´ ımica, Universidade Federal Rural do Rio de Janeiro, 23851-970, Serop ´ edica, Rio de Janeiro, Brazil 2 Setor de Qu´ ımica de Produtos Naturais, Universidade Estadual do Norte Fluminense, 28015-620, Campos, Rio de Janeiro, Brazil 3 Departamento de F´ ısico-Qu´ ımica, Universidade Federal Fluminense, Niter ´ oi, Rio de Janeiro, Brazil 4 Departamento de Qu´ ımica, Universidade Federal de S ˜ ao Carlos, 13565-905, S ˜ ao Carlos, S ˜ ao Paulo, Brazil 5 Nucleo de Pesquisa em Produtos Naturais, Universidade Federal do Rio de Janeiro, 21941-590, Rio de Janeiro, Brazil Received 28 January 1999; revised 20 April 1999; accepted 21 April 1999 ABSTRACT: An NMR study of two known bis-indole alkaloids is described. In addition to conventional 1D NMR methods, 2D shift-correlated NMR experiments [ 1 Hx 1 H-COSY, 1 Hx 13 C-HMQC- 1 J(C,H), 1 Hx 13 C-HMBC- n J(C,H) (n D 2 and 3)] and 2D 1 Hx 1 H-NOESY were used for 1 H and 13 C chemical shift assignments of these alkaloids. Copyright  1999 John Wiley & Sons, Ltd. KEYWORDS: bis-indole alkaloids; NMR; 1D NMR; 2D NMR; 1 H NMR; 13 C NMR; chemical shift assignments INTRODUCTION Alkaloids are secondary metabolites detected in plants and animals, with great potential applications in taxonomy, ecology and medicine. 1,2 This paper reports the 1 H and 13 C chemical shift assignments of two known bis-indole alkaloids, conodurine (1) and voacamine (2), isolated from the Brazilian plant Tabernaemontana laeta Mart. (Apocynaceae). The results of the extensive application of 1D ( 1 H NMR, HBBD- 13 C NMR and DEPT- 13 C NMR) and 2D [ 1 Hx 1 H-COSY, 1 Hx 13 C-HMQC- 1 J(C,H), 1 Hx 13 C-HMBC- n J(C,H) (n D 2 and 3), 1 Hx 1 H-NOESY] spectral techni- ques 3 were used to identify the structures (1 and 2) and to establish the complete 1 H and 13 C resonance assign- ments of these two bis-indole alkaloids, which were also utilized to confirm 13 C NMR data already published in the literature. 4 The complete 1 H and 13 C spectral assignment of this important class of natural products serves to build up a database for the elucidation of novel alkaloids and is useful in fully understanding the correlations between their molecular conformation and biological activity. To the best of our knowledge, 13 C NMR spectral data for 2 and complete chemical shift assignments of hydro- gen atoms of 1 and 2 are hitherto unreported. * Correspondence to : R. Braz-Filho, Setor de Qu´ ımica de Produtos Nat- urais, Universidade Estadual do Norte Fluminense, 28015-620, Campos, Rio de Janeiro, Brazil. Contract/grant sponsor : Programa de Apoio ao Desenvolvimento Cien- t´ ıfico e Tecnol´ ogico (PADCT). Contract/grant sponsor : Financiadora de Estudos e Projetos (FINEP). Contract/grant sponsor : Funda¸ c˜ ao Estadual do Norte Fluminense (FENORTE). These two alkaloids were isolated during a phytochem- ical investigation of a specimen of the plant Tabernae- montana laeta Mart. (Apocynaceae), an arboreal species native to the Atlantic Forest and known popularly as ‘esperta’ and ‘guarana’ in Fluminense North, Rio de Janeiro State, Brazil. EXPERIMENTAL Plant material and isolation of the constituents Tabernaemontana laeta Mart was collected in Bom Jesus do Itabapoana, Rio de Janeiro State, Brazil, and identified by Dr. A. J. M. Leeuwenberg of the Agricultural Univer- sity of Wageningen, The Netherlands. A voucher specimen (WAG) is deposited at the herbarium of the Agricultural University of Wageningen. The dried and powdered root bark (1.06 kg) from T. laeta Mart. was extracted at room temperature using hexane, CH 2 Cl 2 and MeOH. The residue (120 g) of the MeOH extract was submitted to partitioning with CHCl 3 –MeOH/H 2 O (3 : 1) and the usual chromatographic methods to furnish 1 (130 mg), 1 C 2 (879 mg) and 2 (315 mg); the mixture of 1 C 2 (879 mg) was rechro- matographed to afford 1 (300 mg) and 2 (230 mg). NMR spectra 1 H and 13 C NMR spectra were measured on a Bruker DRX 400 spectrometer operating at 400 MHz for 1 H and Copyright  1999 John Wiley & Sons, Ltd. CCC 0749–1581/99/090676–06 $17.50