Structure±Activity Relationship Studies of Putaminoxins and Pinolidoxins: Phytotoxic Nonenolides produced by Phytopatho- genic Phoma and Ascochyta Species‡ Antonio Evidente, 1 Renato Capasso, 1 Anna Andol®, 1 Maurizio Vurro 2 and Maria Chiara Zonno 2 1 Dipartimento di Scienze Chimico-Agrarie, Universita Á di Napoli Federico II, Via Universita Á 100, 80055 Portici, Italy 2 Istituto Tossine e Micotossine da Parassiti Vegetali, CNR, Viale L. Einaudi 51, 70125 Bari, Italy ABSTRACT Putaminoxin and pinolidoxin, two structurally related nonenolides, isolated respectively from organic extracts of Phoma putaminum and Aschochyta pinodes cultures, together with some of their natural analogs and synthetic derivatives, were used in a structure±activity relationship study. Their phytotoxic, antifungal and zootoxic activities were assayed with the aim to ®nd compounds with potential herbicidal properties. The strongest phytotoxic compounds proved to be putaminoxin and pinolidoxin, whose activity appeared to be correlated to the integrity of the nonenolide ring and to the presence of both the hydroxy groups and the unmodi®ed propyl side chain. None of the assayed nonenolides showed antifungal activity, whereas pinolidoxin analogs and derivatives showed high to weak zootoxicity. Copyright  1998 John Wiley & Sons, Ltd. Key words: putaminoxin; pinolidoxin; putaminoxin: analogs and derivates; pinolidoxin analogs and derivatives; phytotoxicity; antifungal activity; mycotoxicity; structure±activity relationships INTRODUCTION During a survey on the production of phytotoxins by weed and crop phytopathogenic fungi, several new phytotoxic nonenolides were isolated, identified and characterized. Nonenolides belong to macrolides, a family of natural compounds with interesting biological properties (Dean, 1963; Richards and Hendrickson, 1964; Manitto, 1981; Turner and Aldridge, 1983). In particular, putaminoxin (1, Figure 1), a disubstituted nonenolide, has been recently isolated as the main toxin (Evidente et al., 1995) from culture filtrates of Phoma putaminum Speg., a fungal pathogen of Erigeron annuus (L.) Pers., an indigenous weed from North America widely present in fields and pastures all over Europe. Later on, other metabolites were isolated from the same culture filtrates, namely putaminoxins B, D and E (2, 3 and 6, respectively, Figure 1), three new nonenolides structurally related to 1 and putaminoxin C (8, Figure 1), a disubstituted cyclononendione containing some struc- tural features similar to those of 1 (Evidente et al., 1997, 1998). Further new phytotoxic nonenolides have been purified and identified from cultures of Ascochyta pinodes Jones, a fungal pathogen responsible for Pea (Pisum sativum L.) antrachnose: pinolidoxin (9, Figure 2) (Evidente et al., 1993a) and three structurally related minor metabolites, namely epi-, dihydro- and epoxy-pinolidoxin (10, 13 and 14, respectively, Figure 2) (Evidente et al., 1993b). Considering the structural similarities of these none- nolides, as well as their interesting chemical and biological characteristics, and the possibility of obtaining some chemical derivatives from the two main toxins, a study on structure–activity relationships was planned. This investigation was carried out using the two toxins (1 and 9) together with the above cited natural analogs and Natural Toxins Nat. Toxins 6: 183±188 (1998) *Correspondence to: Professor A. Evidente, Dipartimento di Scienze Chimico-Agrarie, Universita Á di Napoli Federico II, Via Universita Á 100, 80055 Portici, Italy. E-mail: evidente@unina.it ‡Dedicated to the memory of Professor G. Randazzo. Sponsors: Italian Ministry of University and Technological Research; (172) DISCA. CCC 1056±9014/98/050183±06 $17.50 Copyright  1998 John Wiley & Sons, Ltd. Received 24 July 1998; Revised 9 August 1998; Accepted 16 October 1998. RESEARCH ARTICLE