Open AccessUnusual Inner-Salt Guaiazulene Alkaloids and bis-Sesquiterpene from the South China Sea Gorgonian Muriceides collaris
Author(s) -
Pinglin Li,
Xiaoling Liu,
Hongyan Zhu,
Xuli Tang,
Xuefeng Shi,
Yonghong Liu,
Guoqiang Li
Publication year - 2017
Publication title -
scientific reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.24
H-Index - 213
ISSN - 2045-2322
DOI - 10.1038/s41598-017-08100-z
Subject(s) - moiety , sesquiterpene , chemistry , stereochemistry , indene , organic chemistry
Three new guaiazulene alkaloids muriceidines A–C ( 1 – 3 ) and one new bis -sesquiterpene muriceidone A ( 4 ), were isolated from the South China Sea gorgonian Muriceides collari s. Muriceidines are the first examples structurally architected by guaiazulene coupling with an inner-salt Δ 1 -pipecolic acid via a unique sp 2 methine-bridged linkage, and the bis -sesquiterpene was comprised by a guaiazulene and a indene units linked through a unprecedented carbon-carbon σ -bond between the high steric bridgehead carbon C-10 of guaiazulene moiety and C-2′ of indene moiety. The chiral compounds 2 – 4 were obtained initially as racemates and further separated by chiral HPLC methods. The inner-salt structures of 1 – 3 and absolute configurations of 2 – 4 were fully elucidated by calculated 13 C NMR, ECD and OR with quantum chemical calculation methods. Compound 1 showed cytotoxicity against K562 cell lines with IC 50 value of 8.4 μ M and antifouling activity against the larvae of the barnacle Balanus albicostatus with EC 50 value of 11.9 μ g/mL and potent therapeutic index (LC 50 /EC 50 = 3.66). Also the racemic (±)- 3 showed cytotoxicities against both HL-60 and K562 cell lines with IC 50 values of 2.2 and 3.7 μ M, respectively. A semisynthetic trial was performed to validate the proposed biosynthetic hypotheses.