Cyclobutane dimer iridoids from Tabebuia argentea Britt. (Bignoniaceae)

Tabebuia argentea Britt. (Bignoniaceae) is a tree native of South America and it is used in folk medicine as anti-inflammatory and against influenza [1]. Previous studies of T. argentea apolar extracts reported the isolation of beta-sitosterol, methyl cinnamate, lapachol, ethyl p-hydroxycinnamate, betulinic acid, 3,4′,5-trihydroxy-7-methoxyflavone, veratric acid, and p-anisic acid [2] while phytochemical studies of the genus Tabebuia led to the characterization of iridoids [3], and flavonoids [4]. As a part of an investigation on plants acclimatized at the El Zoharia Research Garden of Cairo, we carried out a phytochemical study of polar extract of the plant. Two new cyclobutane dimer iridoids, one new pinoresinol type lignan, together with many known iridoids and flavonoids, were isolated and characterized from the aerial parts methanol extract. Their structures were elucidated by 1D and 2D NMR spectroscopy, as well as ESI mass spectrometry. In the framework of a screening to search for natural compounds as HSP90 inhibitors, all T. argentea isolated compounds were tested through Surface Plasmon Resonance, a technique that allowed to study the protein/ligand interaction [5]. Some iridoids bound the protein with a good affinity constant.

References: 1. Agra, M.F. (1996) Plantas de Medicina popular dos Cariris Velhos, Paraiba Brasil: espécies mais comuns. Editora União, João Pessoa, Brasil.

2. Barbosa-Filho, J.M. et al (2004) Phyton: 221–228.

3. von Poser, G.L. et al (2000) Biochem. Syst. Ecol. 28: 351–366.

4. Prakash E.O., Rao J.T. (1999) Fitoterapia 70: 287–289.

5. Dal Piaz, F. et al. (2009)J. Med. Chem. 52: 3814–3828.