Abhinandan Shrestha

• This research was successful in creating a polyphenolic profile of the leaves of 100 Rhododendron species from six subgenera. The polyphenolic profile of the fruits and flowers of a few Rhododendron species was also studied. This was achieved by using the technique of liquid chromatography coupled to mass spectrometry. Compounds were identified based on their retention time, UV absorption, fragmentation pattern and high resolution mass data. The leaves of Rhododendron species were determined to be a good source of polyphenolic secondary metabolites with a total of 348 polyphenols identified. Out of 348 compounds, 221 compounds were novel in Rhododendron species and 7 compounds were novel in nature. The most abundant compounds included quercetin derivatives, protocatechuic acid-O-hexoside, catechin, epicatechin, procyanidin A and B dimers, kaempferol-O-rhamnoside, p-coumaric acid-O-hexoside, 3-O-caffeoylquinic acid and 5-O-caffeoylquinic acid. From the identified secondary metabolites in Rhododendron species, a few marker compounds were identified for some individual Rhododendron species and also for the six subgenera. The use of polyphenolic secondary metabolites as chemotaxonomic markers needs to be assessed. Multivariate statistical analysis was carried out to investigate whether phytochemistry, phylogeny and biological activity showed any correlation. The relative quantities of polyphenolic compounds were compared using box plots. Some compounds were found in higher intensity in certain subgenus. Some isomers of these compounds were found to be relatively more abundant than others. PCA plots and hierarchical clustering plot were generated using LC-TOF-MS data and it was determined that the genetically similar Rhododendron species produces a diverse variety of secondary metabolites. The number of compounds present in Rhododendron species was found to have no correlation to the ploidy level or their anti-bacterial activity against Bacillus subtilis.