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I would like to know how you go about synthesising glycosides of flavonoids and stilbenoids from their respective sugars and flavonoids/stilbenoids. I read http://www.netsci-journal.com/97v1/97005/005p20.htm but I found it too specific (as it only applied to aliphatic compounds) and required an enzymatic catalyst that is impossible to predict. I would like a general formula that if it does contain an enzymatic catalyst the enzyme is either constant or at least usually predictable.

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Could you clarify what you mean by a 'constant or usually predictable enzyme'? –  Tanith Rosenbaum Jan 23 '13 at 16:40
An enzyme that doesn't change (i.e. is constant) or is predictable by some mathematical model. –  Brenton Horne Jan 23 '13 at 16:49
My educated guess would be that such an enzyme does not exist. Enzymes are usually very specific to their substrates. As for predictability, it is possible to model an enzyme to a desired substrate using computational methods (i.e. Molecular Modelling). However you might be better off looking into classical organic synthesis methods, retrosynthesis specifically. –  Tanith Rosenbaum Jan 23 '13 at 17:51
In terms of process, sugars tend to be exceedingly insoluble in organic media. Simple per-acetylation of glucose is not a high yield reaction. If the glucose is ball-milled overnight (lapidary tumbler no more than 1/3 full including grinding balls), the micronized glucose reacts in very good yield. There are other tricks to helping things move along one you have the synthesis itself. –  Uncle Al Apr 18 at 14:58

1 Answer 1

I suggest to forget about the enzymes.

Pepare for a probably lengthy synthesis - you will need patience and a clever protection/deprotection scheme.

The following is definitely not applicable to all starting materials but might give some directions.

quercetin numbering and acetal formation

If the flavonoid contains a catechol moiety, just like quercetin (1), the vicinal phenolic $\ce{OH}$ groups can be protected as an acetal by heating the starting material with $\alpha,\alpha$-dichlordiphenylmethane in diphenylether (DOI). The protecting groups is easily removed by hydrogenation over $\ce{Pd/C}$ at 1 atm.

Note that the PMB (4-methoxybenzyl) group is another protecting group for (phenolic) $\ce{OH}$ that gets off by hydrogenation.

As far as selectivities for the protection of the other $\ce{OH}$ groups in 1 are concerned, have a look at the 1962 paper by Leonard Jurd, who described that the methylation of quercetine pentaacetate in dry acetone predominantly furnishes 7-O-methylquercetin. There are quite some more recent articles citing this!

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