A new cyclopeptide, ophiorrhisine A (1), a new tetrahydroisoquinoline alkaloid, 7',10-dide-O-methylcephaeline (2), two known β-carboline alkaloids, and four known tetrahydroisoquinoline alkaloids were isolated from Ophiorrhiza nutans (Rubiaceae). Compound 1 is a tetrapeptide possessing a 14-membered paracyclophane ring and a novel N,N,N-trimethyltyrosine residue in the side chain. The stereochemistry at the aryl-alkyl ether bond was different from that of other known 14-membered paracyclophanes. The structure of 2 was established by spectroscopic analysis and semisynthesis.
The first asymmetric total synthesis
of ophiorrhisine A (1), a new cyclic tetrapeptide isolated
from Ophiorrhiza nutans, was accomplished
via an intramolecular
aromatic nucleophilic substitution reaction (IMSNAr) of
a linear tripeptide to construct a 14-membered paracyclophane ring,
resulting in confirmation of its structure and absolute configuration.
The structure–activity relationship study of 1 and its derivatives demonstrated that some derivatives possessed
cytotoxicity toward human cancer cell lines A549, HT29, and HCT116.
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