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Structure Elucidation of the Main Tetrahydroxyxanthones of Hypericum Seeds and Investigations into the Testa Structure
Author(s) -
Lorenz Peter,
Heller Annerose,
Bunse Marek,
Heinrich Miriam,
Berger Melanie,
Conrad Jürgen,
Stintzing Florian C.,
Kammerer Dietmar R.
Publication year - 2018
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.201800035
Subject(s) - chemistry , hypericum perforatum , hypericum , xanthone , williamson ether synthesis , silica gel , chromatography , extraction (chemistry) , ether , stereochemistry , organic chemistry , botany , traditional medicine , medicine , biology
Seeds from Hypericum species have recently been identified as an interesting source of xanthone derivatives. Extraction of seeds from H . perforatum with Me OH and subsequent concentration via polyamide adsorption yielded a fraction enriched in tetrahydroxyxanthones ( THX ), which were further semipurified by silica gel chromatography. Based on tentative structure assignment of the two main THX X1 and X2 by NMR a total synthesis was performed for both compounds ( THX 1 and 2 , respectively), starting with an Ullmann ether synthesis. The synthesized 1 and 2 were characterized via 1D‐ and 2D‐ NMR methods as well as by LC / HR ‐ MS analysis and proven to be 1,4,6,7‐ THX ( 1 ) and 1,2,6,7‐ THX ( 2 ). Final structure assignment of the natural Hypericum THX constituents was accomplished by comparing chromatographic and spectroscopic data ( LC / MS n and GC / MS ) with those of 1 and 2 which were obtained by synthesis. Beyond, investigations into the seeds of H . perforatum and H . tetrapterum by scanning electron microscopy ( SEM ) provided insights of the structure of the testa (seed coat), which is established by two cell layers, with the lignified sclerenchyma presumably being the depository of the xanthones.