Antifungal activity of alkyl and heterocyclic aza-derivatives of gossypol as well as their complexes with NaClO 4 against Fusarium oxysporum f. sp. lupini Piotr Przybylski a, * , Krystian Pyta a , Dorota Remlein-Starosta b , Grzegorz Schroeder a , Bogumil Brzezinski a , Franz Bartl c a Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland b Institute of Plant Protection, Miczurina 20, 60-318 Poznan, Poland c Institute of Medical Physics and Biophysics Charité, Universitätsmedizin Berlin Campus Charité Mitte, Ziegelstr. 5/9, 10117 Berlin, Germany article info Article history: Received 26 January 2009 Revised 9 February 2009 Accepted 9 February 2009 Available online 20 February 2009 Keywords: Gossypol aza-derivatives Fusarium oxysporum Antifungal activity Spectroscopy ESI + and ESI  MS abstract Eight alkyl and six heterocyclic aza-derivatives of gossypol (2–15) have been synthesized using gossypol (1) extracted from Gossypium Herbaceum cottonseeds. The ability of gossypol aza-derivatives to form complexes with NaClO 4 has been investigated by electrospray ionisation (ESI) mass spectra recorded in the positive and negative ion detection modes. The gossypol aza-derivatives have been characterized by FT-IR, 1 H and 13 C NMR spectroscopic methods and subsequently tested for their antifungal properties against Fusarium oxysporum. Four alkyl aza-derivatives (2–5), present in the enamine–enamine tauto- meric form, have shown activity comparable or higher than that of gossypol against this fungus. To improve the antifungal activity the complexes of the most active compounds 2–5 with NaClO 4 were pre- pared. Complexes of 2 and 5 with NaClO 4 have shown antifungal activity higher than that of the uncom- plexed compounds. Ó 2009 Elsevier Ltd. All rights reserved. Gossypol is a yellow pigment, present in various parts of the cotton plants 1 , which has drawn the attention of many scientist because of its wide biological activities such as contraceptive, 2 anticancer, 3 antiviral 4 or antimicrobial. 5 Despite these interesting and potentially useful effects, the application of gossypol as a ther- apeutic or antimicrobial agent still remains a challenge because of a number of serious sides effects. 6 A convenient way to obtain less toxic compounds based on gossypol is to block the gossypol alde- hyde groups by their conversion into, for example, Schiff bases, hydrazones, nitriles etc. Up to now various thio-, aza- and aza- modifications of gossypol have been tested in order to obtain less toxic derivatives which would extend the fields of its application. 7 From earlier studies it is known that the tautomeric forms of gos- sypol aza-derivatives (Fig. 1) depend on the nature of the substitu- ent directly bonded to N16 and N16 0 atoms. 8 The fungus Fusarium oxysporum is a worldwide serious problem because induction of wilt disease in a wide range of host plants such as, for example, cereals, tomatoes, potatoes, bananas and watermelons. 9 This plant pathogenic fungus strain produces poi- sonous chemical compounds like mycotoxins (e.g., Fusaric acid) which contaminate harvested crops. Ingestion of cereals vegetables or fruits affected by the disease evoked by the Fusarium oxysporum may give rise to allergic symptoms or be carcinogenic by long-term consumption in humans and animals due to the presence of myco- toxins produced by the fungus. 10 Gossypol antifungal activity is concerned with its protecting role of cotton plants against many pathogens like, for example, Rhizocto- nia Solani. 11 Recently, Turco et al. investigated in vitro the effect of gossypol and its mixture with NaCl on conidial germination and via- bility of Fusarium oxysporum sp. Vasinfectum isolates. 12 These authors have reported that the inhibitory effect against Fusarium oxysporum is significant at gossypol concentrations between 10 and 20 mg/L, while the addition of the salt reduces the antifungal activity of gossypol. Up to now many derivatives, especially fluorine derivatives of various heterocycles 13 , have been tested against Fusarium oxysporum in contrast to gossypol aza-derivatives whose antifungal activity in this field is unexplored. This fact has motivated our group to undertake synthesis and biological tests of a series of gossypol aza-derivatives containing alkyl and heterocyclic moieties and their complexes with NaClO 4 against the pathogenic fungus. Gossypol was extracted 14 from cottonseeds of Gossypium herbaceum and subsequently converted into its eight Schiff bases and six hydra- zones by a simple condensation of amines and hydrazines with the two aldehyde groups of gossypol in dichloromethane. 15 The structures of all Schiff bases and hydrazones of gossypol were determined by the ESI MS, FT-IR and NMR methods. 16,17 The FT-IR spectra of gossypol Schiff bases and gossypol hydrazones are signif- icantly different in the m(C@O) range. In the spectra of gossypol Schiff bases (2–9) an intense band at about 1640 cm 1 , assigned to the 0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2009.02.051 * Corresponding author. Tel.: +48 61 8291252; fax: +48 61 829 1505. E-mail address: piotrp@amu.edu.pl (P. Przybylski). Bioorganic & Medicinal Chemistry Letters 19 (2009) 1996–2000 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl