The distribution of iridoids in Bignoniaceae

The distribution of iridoids among the tribes of Bignoniaceae is shown. In the present work, 18 species from the tribes Bignonieae and Tecomeae as well as one from Eccremocarpae have been investigated. These data combined with those obtained through a literature review were analysed and showed that iridoids occur predominantly in the tribe Tecomeae. In this tribe, a chemical distiction between the genera Tabebuia and Tecoma was observed: The iridoids in Tabebuia are decarboxylated whereas in Tecoma they are C-4 formylated. The species from Bignonieae are poorly investigated and only few reports have been published, however, the iridoids found are mainly C-4 carboxylated. The only exception, Dolichandra cynanchoides (= Macfadyena cynanchoides), with decarboxylated iridoids, is also morphologically abnormal in Bignonieae.