Glycosidase-catalyzed synthesis of glycosyl esters and phenolic glycosides

Session: 
S4.3 Synthetic innovation in glycan assembly
Code: 
OL4.3.4
Location (hall): 
Galactose
Start/end time: 
Tuesday, July 2, 2019 - 12:30 to 12:45
Vladimír
Kren

Vladimír Kren1, Ivan Bassanini2, Lucie Petraskova1, Jana Kapesova1, Sergio Riva2

1Institute Of Microbiology, Cas, Prague, Praha, Czech Republic, 2Istituto di Chimica del Riconoscimento Molecolare, Consiglio Nazionale delle Ricerche, Milano, Italy

Glycosides of phenolic acids and of derivatives of hydroxycinnamic acids are ubiquitous in plants, however their isolation from plant material is very tedious. Most of phenolic acid glycosides are glycosylated on the aromatic hydroxyls. However, glycosides attached to the carboxylic moiety can also be rarely found (glycosyl esters; typically β-glucopyrano-sides). Their chemical synthesis is not trivial and involves inherent problems of high lability of glycosyl ester bond, which is incompatible with most acyl protection groups. Glycosides of phenolic acids and of derivatives of hydroxycinnamic acids are ubiquitous in plants, however their isolation from plant material is very tedious. Most of phenolic acid glycosides are glycosylated on the aromatic hydroxyls.

However, glycosides attached to the carboxylic moiety can also be rarely found (glycosyl esters; typically β-glucopyrano-sides). Their chemical synthesis is not trivial and involves inherent problems of high lability of glycosyl ester bond, which is incompatible with most acyl protection groups. Enzymatic approach mimicking in vivo biosynthesis employs glucosyltransferases but this method uses expensive UDP-glucose and the yields are low. We have recently described new robust diglycosidase rutinosidase from A. niger, which is able to glycosylate various acceptors including phenols [1] in a good yield using cheap rutin (1) as a glycosyl donor. To our great surprise glycosyl esters were also formed at a reasonable yield. We tested this reaction with a large panel of various phenolic acids and as an example we demonstrate rutinosylation of p-coumaric acid yielding phenolic glycoside (4) and respective glycosyl ester (5). A broader application of this new type of reaction was demonstrated by the synthesis of respective glycosyl esters of p-, m-, o-coumaric acids, ferulic acid and others. Rutinosides can be treated in situ with alpha-L-rhamnosidase (A. terreus) to yield respective β-glucopyranosides. Enzymatic glycosylation of cinnamic acid derivatives is also linked to their (E)-(Z) isomerization in which a quinone intermediate is involved. We describe here probably the first example of glycosylation of a carboxyl group with a glycosidase.

Scheme. Rutinosylation of p-coumaric acid (3) with rutinosidase from A. niger

Acknowlegements

Czech Science Foundation project 18-00150S and the joint Czech-Italian AVČR-CNR (V.K. & S.R.) mobility project No. CNR-16-30 are acknowledged.

References: 
  1. Šimčíková D.; Kotik M.; Weignerová L.; Halada P.; Pelantová H.; Adamcová K.; Křen V. Adv.Synth. Catal. 2015, 357, 107-117.

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