Studies On The Chemical Constituents And The Biological Activities Of Rhododendron Micranthum

A hyphae formation inhibition bioassay (HFIB) in Streptomyces85E was apreliminary assay method to identify protein kinase inhibitors. As part of an ongoingsearch for novel protein kinase inhibitors from traditional Chinese medicines, theextract of the leaves of Rhododendron micranthum showed strong inhibitory effect toStreptomyces85E in HFIB. HFIB guided isolation resulted in5new sesquiterpenoids(15), together with12known sesquiterpenoids (617),4known Grayanotoxin(1821),4known triterpenoids (2225)，4known flavonoids (2629)，2knownphenolic compounds (30,31)，3known coumarins (3234). The planar structure andrelative configuration of compound1was determined on the basis of1D NMR,2DNMR, and single crystal X-ray diffraction. In order to determine the absoluteconfiguration of compound1,3derivatives containing a bromine atom (1a,1b,1c)were synthesized from compound1, and a suitable crystals of compound1b and1cwere selected for single-crystal X-ray diffraction. The absolute configuration ofcompound1was unambiguously determined by the single-crystal X-ray diffractionanalysis performed on1b and1c. New compounds25were determined based on theNMR analysis, chemical transformation to1, and in consideration of the biogeneticrelationship. Compound1showed strong activity in the hyphae-formation inhibitionassay in Streptomyces85E.1showed very low toxicity to Plutella xylostella.Compounds15，1a，1b, and1c were evaluated to their inhibitory activities againsthuman11β-HSD1, and cytotoxicity against HL-60, SMMC-7721, A-549, MCF-7, andSW480cells lines, and1b and1c showed moderate cytotoxicity against five cancercell lines.