Diterpenoids from the Flowers of Rhododendron molle

Abstract

A new seco-kalmane-type diterpenoid, seco-rhodomollone (1), five new grayanane-type diterpenoids, rhodomollein XXI (2), 6-O-acetylrhodomollein XXI (3), 6,14-di-O-acetylrhodomollein XXI (4), rhodomollein XXII (5), and 2-O-methylrhodomollein XI (6), and two new kalmane-type diterpenoids, rhodomolleins XXIII (7) and XXIV (8), together with seven known compounds, were isolated from the flowers of Rhododendron molle collected in Guangxi Province, China. The absolute configurations of 1 and 3 were defined by single-crystal X-ray diffraction experiments. Compound 1 possesses an unprecedented 1,5-seco-kalmane skeleton presumably derived by cleavage of the C-1-C-5 bond of the kalmane skeleton. Compounds 2-4 represent the first examples from a natural source of grayanane-type diterpenoids with a chlorine substituent.

Bioactivity in Rhododendron: A Systemic Analysis of Antimicrobial and Cytotoxic Activities and Their Phylogenetic and Phytochemical Origins

“…While for several species, various antimicrobial activities had been reported (Popescu and Kopp, 2013), chemical compounds responsible for a certain bioactivity had been identified only for individual cases (Zhou et al, 2014; Li et al, 2015). Here, we aim at predicting candidate compounds with antimicrobial activity from a large compilation of Rhododendron leaves.…”

Total Syntheses of Rhodomolleins XX and XXII: A Reductive Epoxide‐Opening/Beckwith–Dowd Approach

“…(> 20:1). [8] To further extend the generality of this reductive epoxideopening/Beckwith-Dowd rearrangement process,t he regioselective fragmentation of cyclopropanol 33,w hich could be prepared from 12 in 75 %yield following Fernµndez-Mateos procedure, [28] was also conducted (Scheme 4). [8] To further extend the generality of this reductive epoxideopening/Beckwith-Dowd rearrangement process,t he regioselective fragmentation of cyclopropanol 33,w hich could be prepared from 12 in 75 %yield following Fernµndez-Mateos procedure, [28] was also conducted (Scheme 4).…”

“…On the other hand, apart from few examples of cascade strategies, [4] theconstruction of the [3.2.1] bicyclicskeletons in the total syntheses of tetracyclic diterpenoids required multistep reaction sequences, [5] which inevitably maximized functional group manipulations and resulted in lengthier synthetic routes.P rompted by this problem, we sought to develop versatile protocols by establishing the [3.2.1] bicyclic motif in am ore straightforward manner.R ecently,i nspired by the oxidative dearomatization-induced (ODI) cycloaddition/ring distortion approaches toward the syntheses of diterpenoid alkaloids, [6] we reported an ODI-[5+ +2] cycloaddition/pinacoltype 1,2-acylm igration cascade reaction, leading to the concise total syntheses of several highly oxidized ent-kauranoids. [7] In continuation of our work in this area, we herein describe the first total syntheses of rhodomolleins XX (5)and XXII (6), two congeners of the grayanoid family,w hich are isolated from Rhododendron molle G. Don (Ericaceae), [8] through an ew titanium(III)-mediated reductive epoxideopening/Beckwith-Dowd rearrangement process.…”

Untitled

“…Grayanane diterpenoids having specialized carbon skeletons with highly oxygenated functionalities are exclusively known to Ericaceae family 41 and is extremely toxic to mammals, especially to the heart and nervous systems 42 . Moreover, lyoniol A, an amyostatic compound 35 is also reported to produce respiratory depression, hypotension 43 and induce paralysis of nerve centers and motor nerve terminals.…”