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First Efficient Syntheses of 1‐, 4‐, and 5‐Caffeoylquinic Acid
Author(s) -
Sefkow Michael,
Kelling Alexandra,
Schilde Uwe
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200107)2001:14<2735::aid-ejoc2735>3.0.co;2-i
Subject(s) - quinic acid , chemistry , hydrolysis , vicinal , protecting group , acid hydrolysis , acetone , organic chemistry , aldol reaction , chloride , diol , stereochemistry , catalysis , alkyl
Abstract Efficient synthesis of 1‐, 4‐, and 5‐caffeoylquinic acid was achieved in three or four steps with suitably protected quinic acid precursors, in overall yields of 41%, 36%, and 60% [from quinic acid ( 1 )]. 1‐Caffeoylquinic acid was prepared by esterification of acetone quinide 7 with caffeoyl chloride 6 , followed by a two‐step hydrolysis of all protecting groups. Caffeoylquinic acids 4 and 5 were prepared from known quinic acid derivatives, 13 and 25 , by selective esterification of the secondary hydroxy groups and hydrolysis with 1 M HCl. However, initial attempts to prepare fully protected quinic acid derivatives with a free hydroxy group only at either C‐4 or C‐5, for the synthesis of 4 and 5 , were not successful. Kinetic acetalization of pentasilylated quinic acid 15 using bis(dimethoxy acetals) afforded several crystalline reaction products which were identified by X‐ray diffraction. Diacetal 20 , derived from a vicinal cis ‐diol, was unambiguously identified for the first time. Unexpectedly, it has two trans ‐diaxially oriented methoxy groups, forcing the quinide ring into a twist‐boat conformation.