Quaternary b-carboline alkaloids from Psychotria prunifolia (Kunth) Steyerm. Emiret O. Faria a , Lucilia Kato a, *, Cecı ´lia M.A. de Oliveira a , Brenda G. Carvalho a , Cleuza C. Silva b , Lilian S. Sales b , Iva ˆnia T.A. Schuquel b , Elisa ˆngela P. Silveira-Lacerda c , Piero G. Delprete c,1 a Instituto de Quı´mica, Universidade Federal de Goia ´s, UFG, Campus II – Samambaia, 74001-970, Goiaˆnia – GO, Brazil b Departamento de Quı´mica, Universidade Estadual de Maringa ´, UEM, Avenida Colombo, 5790, 87020-900, Maringa ´ – PR, Brazil c Instituto de Cieˆncias Biolo ´gicas, Universidade Federal de Goia ´s, UFG, Campus II – Samambaia, CEP 74001-970, Goia ˆnia – GO, Brazil 1. Introduction Psychotria L. sensu lato is one of the largest genera of the Rubiaceae family (and one of the largest in the Angiosperms) comprising about 1700 species worldwide. However, the genus is clearly paraphyletic, and several genera have been recently separated from it; therefore the phylogenetic relationships among the tribe Psychotrieae remain ambiguous. Previous chemical investigation on this genus revealed the presence of several secondary metabolites including pyrrolidinoindolines (Verotta et al., 1998; Jannic et al., 1999), quinolines (Solis et al., 1997), and terpenoid isoquinoline alkaloids (Nomura et al., 2008), some of which have been reported to possess pharmacological activities like cytotoxic, antimalarial, and antileishmanial activities (Muhammad et al., 2003). Recently, the extracts of Psychotria and the closely related genus Palicourea were screened at the US National Cancer Institute for their activities against human cancer (one-dose/60-cell- line prescreen), and these two genera were selected as ‘hot’ genera from over 90,000 extracts assayed (Cragg et al., 2006). In the search to find potential antitumor constituents from plants of the Brazilian cerrado, we have investigated promising extracts of several Rubiaceae species. In a preliminary experi- ment we observed that the ethanol extract of P. prunifolia exhibited a weak cytotoxic activity (IC 50 > 1000 mg ml 1 ) for S180 (sarcoma) and K562 (myeloid leukaemia) cells. In spite of this low-level activity we carried out a chemical investigation of this EtOH extract and isolated two new b-carboline alkaloids, compounds 1 and 2, along with the known strictosamide 3. The structures of 1 and 2 were determined by 1D and 2D NMR, IR, and HRMS. 2. Results and discussion The alkaloid 1 was obtained as a yellowish oil and was positive to Dragendorff’s test. The IR absorptions at 1641, 1579, and 1079 cm 1 suggested the presence of amine and aromatic groups HRMS revealed a [M] + signal at m/z 291.1458, corresponding to a molecular formula of C 19 H 19 N 2 O (calculated m/z 291.1497), which requires 12 degrees of unsaturation. The 13 C NMR spectrum of 1 indicated the presence of 19 carbon atoms (Table 1), including six aliphatic, two olefinic, and 11 aromatic carbons. The DEPT spectrum showed the absence of CH 3 groups, with the presence of four methylenes, 10 methines, and five sp 2 quaternary carbons. Information from the 1 H– 1 H COSY and the HMQC spectra pointed to a proton spin system ranging from H-5 [d 8.33 (d, J = 6.6 Hz), d C 132.5] to H-6 [d 8.41 (d, J = 6.6 Hz), d C 116.0], and a second one ranging to H-9 [d 8.28 (d, J = 8.1 Hz), d C 122.8], over H-10 [d 7.48 (t, J = 8.1 Hz), d C 122.4] and H- 11 to H-12 [d 7.76–7.91 (m), d C 132.3 and 113.2]. In addition to these Phytochemistry Letters 3 (2010) 113–116 ARTICLE INFO Article history: Received 16 September 2009 Received in revised form 24 February 2010 Accepted 26 February 2010 Available online 15 March 2010 Keywords: Psychotria prunifolia Indolic alkaloid Rubiaceae Psychotriae S-180 K-562 ABSTRACT Two new quaternary alkaloids, compound 1 and the 14-oxo derivative 2, were isolated along with the known alkaloid strictosamide (3) from the leaves of Psychotria prunifolia (Kunth) Steyerm. (Rubiaceae, Psychotriae). Their structures were elucidated using spectroscopic methods (1D and 2D NMR, IR, and HRMS). ß 2010 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +55 62 35211016/208; fax: +55 62 35211167. E-mail address: lucilia@quimica.ufg.br (L. Kato). 1 Current address: Herbier de Guyane, Institut de Recherche pour le De ´ veloppe- ment - IRD, B.P. 165, 97323 Cayenne Cedex, French Guiana, France. Contents lists available at ScienceDirect Phytochemistry Letters journal homepage: www.elsevier.com/locate/phytol 1874-3900/$ – see front matter ß 2010 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.phytol.2010.02.008