Dicaffeoylquinic acid (DCQA) is a natural polyphenolic compound widely distributed in plants such as coffee beans, which possesses a range of pharmacological activities. Herein, is reported studies undertaken towards the first total synthesis of 3,5-DCQA conjugates. Two synthetic routes were investigated. The first route involves a seven step sequence beginning from quinic acid. The overall yield via this synthetic approach was 30%. The key steps involved in the sequence were a regioselective benzylation of the C-3-hydroxyl group followed by silyl protection of the C-1 and C-4 hydroxyl groups. Deprotection of the benzyl group by hydrogenolysis and opening of the lactone afforded the 3,5-diol. Esterification of the 3,5-diol with 3,4-tert-butyldimethylsilyl caffeoyl chloride afforded the di-ester. Removal of the protecting groups afforded 3,5-DCQA. The second route involved selective protection of the C-3-hydroxyl group with silyl followed by benzylation of the C-1 and C-3 hydroxyl groups. Saponification of the lactone ring followed by benzylation of the carboxylic acid gave the benzyl ester. Silyl deprotection afforded the 3,5-diol. The 3,5-diol was subsequently esterified by refluxing in toluene with commercially available Meldrum’s acid. In the final step, the synthesis of 3,5-DCQA was achieved by a Knoevenagel condensation of 3,4-dihydroxybenzaldehyde and a malonate ester of quinic acid. An efficient method for the synthesis of possible metabolites of quinic acid conjugates was also described. This protocol employs N-(4-methoxyphenyl)-trifluoroacetimidate glucuronyl as the donor. The key reaction in this sequence was the coupling of N-(4-methoxyphenyl)-trifluoroacetimidate glucuronyl with 4-hydroxy-3-methoxy-benzaldehyde.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:552610 |
| Date | January 2011 |
| Creators | Raheem, Kolawole Saki |
| Contributors | Botting, Nigel P. |
| Publisher | University of St Andrews |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10023/2009 |
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