The Condensation of Salicylaldehydes and Malononitrile Revisited: Synthesis of New Dimeric Chromene Derivatives Marta Costa, Filipe Areias, Luı ´s Abrunhosa, † Armando Vena ˆncio, † and Fernanda Proenc ¸ a* Centro de Quı ´mica, UniVersidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal fproenca@quimica.uminho.pt ReceiVed NoVember 28, 2007 The reaction of salicylic aldehydes with malononitrile was reinvestigated, and the reaction pathway was followed by 1 H NMR spectroscopy. A delicate control of the experimental conditions allowed the synthesis of 2-imino-2H-chromene-3-carbonitriles 1, (2-amino-3-cyano-4H-chromen-4-yl)malononitriles 2, 4-amino- 5-imino-2,7-dimethoxy-5H-chromeno[3,4-c]pyridine-1-carbonitrile 12, and (4,5-diamino-1-cyano-1,10b- dihydro-2H-chromeno[3,4-c]pyridin-2-ylidene)malononitrile 13. Two novel 2-iminochromene dimers, with structures 8 and 9, were isolated and fully characterized. The activity of compound 8a on Aspergillus spp. growth and on ochratoxin A production was evaluated. The results of the bioassays indicate that compound 8a, applied at concentrations of 2 mM, totally inhibited the growth of the fungi tested. Ochratoxin A production by Aspergillus alliaceus was reduced by about 93% with a 200 μM solution of this compound. A moderate inhibitory effect was observed for the analogous structure 8b, and no inhibition was registered for compounds 2 and 1, used as synthetic precursors of the dimeric species 8. Introduction Chromene derivatives are an important class of compounds, widely present in plants, including edible vegetables and fruits. 1 Numerous bioactive natural products have been identified, and the presence of the chromene-based structure has been associated with the capacity to prevent disease. 2 Synthetic analogues were developed over the years, some of them displaying remarkable effects as pharmaceuticals, 3 including antifungal 4 and antimi- crobial activity. 5 The classic method for the synthesis of 2-iminochromenes is the Knoevenagel condensation of salicylic aldehydes with active methylene compounds, followed by intramolecular cy- clization. A detailed analysis of the reports on the reaction of salicylaldehyde and malononitrile 6 indicates that a delicate control of solvent, temperature, and ratio of reagents are determinant for the incorporation of 1, 2, or 3 molar equiv of malononitrile in the aldehyde unit. 6b Compounds 1-4 (Figure 1) were identified as the products of this reaction, formed in the presence of base, at room temperature, either using ethanol 6a-d or water 6e as solvent. † BB - Institute for Biotechnology and Bioengineering, Centre for Biological Engineering, Universidade do Minho, Campus de Gualtar 4710-057, Braga, Portugal. (1) Curini, M.; Cravotto, G.; Epifano, F.; Giannone, G. Curr. Med. Chem. 2006, 13, 199-222. (2) O’Kennedy, P., Thornes, R. D., Eds. In Coumarins: Biology, Applications and Mode of Action; J. Wiley & Sons: Chichester, 1997. (3) For recent examples of biologically active chromene derivatives, see: (a) Yu, D.; Suzuki, M.; Xie, L.; Morris-Natschke, S. L.; Lee, K.-H. Med. Res. ReV. 2003, 23, 322-345. (b) Khan, K. M.; Saify, Z. S.; Khan, M. Z.; Choudhary, M. I.; Perveen, S.; Chohan, Z. H.; Supuran, C. T.; Zia- Ullah; Atta-Ur-Rahman. J. Enz. Inhib. Med Chem. 2004, 19, 373-379. (c) Abd El-Aziz, A. S.; El-Agrody, A. M.; Bedair, A. H.; Corkery, T. C.; Ata, A. Heterocycles 2004, 63, 1793-1812. (d) Borges, F.; Roleira, F.; Milhazes, N.; Santana, L.; Uriarte, E. Curr. Med. Chem. 2005, 12, 887-916. (e) Chimenti, F.; Bizzarri, B.; Bolasco, A.; Secci, D.; Chimenti, P.; Carradori, S.; Granese, A.; Rivanera, D.; Lilli, D.; Scaltrito, M. M.; Brenciaglia, M. I. Eur. J. Med. Chem. 2006, 41, 208-212. (f) Kulkarni, M. V.; Kulkarni, G. M.; Lin, C. H.; Sun, C. M. Curr. Med. Chem. 2006, 13, 2795-2818. (4) (a) Tangmouo, J. G.; Meli, A. L.; Komguem, J.; Kuete, V.; Ngounou, F. N.; Lontsi, D.; Beng, V. P.; Choudhary, M. I.; Sondengam, B. L. Tetrahedron Letters 2006, 47, 3067-3070. (b) Abd-El-Aziz, A. S.; El- Agrody, A. M.; Bedair, A. H.; Corkery, T. C.; Ata, A. Heterocycles 2004, 63, 1793-1812. (c) Khafagy, M. M.; Abd El-Wahab, A. H. F.; Eid, F. A.; El-Agrody, A. M. Farmaco 2002, 57, 715-722. 1954 J. Org. Chem. 2008, 73, 1954-1962 10.1021/jo702552f CCC: $40.75 © 2008 American Chemical Society Published on Web 02/14/2008