by X. doucetiae revealed the presence of several similar amide derivatives. Unfortunately, most of these compounds are only produced in very small amounts but they could be easily synthesised. Thus, we tried to elucidate their structure without actually isolating them by following their chemical synthesis in order to obtain enough for bioactivity testing. From feeding experiments followed by HPLC/MS and GC/MS experiments we were able to elucidate the structure of 26 derivatives of this simple class of compounds. In order to determine structure–activity relationships, we synthesised two series of different acyl derivatives of the identified phenylethylamine and tryptamine derivatives. Determination of their cytotoxic activity revealed a clear correlation with their acyl chain length.