Could you explain an esterification method using coupling reagents or any other method between 1. a very hydrophilic compound having a carboxylic part and 2. weak hydrophobic alcohols like cholesterol? I encountered the problem of choosing the appropriate solvent and reagents to accomplish the reaction.
I thank previously
i suggest you may choose DMF as a solvent, in which the hydrophilic compound and lipophilic alcohol are easily dissolved. DCC or DIC could be the suitable coupling reagents.
and another method: the carboxylic compound dissolved in THF: H2O (3:1) was added NHS, EDCI, crown ether. after 30min reacting, the alcohol was added and the mixture is stirred for 24 hour.
Make the acid chloride by reacting the carboxylic acid with SOCl2 or cat. oxalyl chloride in DMF.
Dear Dr. Lu and Dr. Yang thanks for your valuable recommendations.
Unfortunately, the hydrophilic compound is insoluble in DMF or THF. It is only soluble in protic solvents. Another problem is that cholesterol is very weak alcohol and if there exists any kind of stronger OH, it would interfere the reaction such as the presence of water or alcohols.
SOCL2 could not be used because there are two positions susceptible for acylation.
Is there a reversible method to reduce hydrophilicity of the compound?
Thanks.
Can you silylate the hydrophilic material, to render it temporarily soluble in organic solvents?
Dear Dr. Demers, thanks a lot for your proper opinion. I am searching about silylation as you suggested, wondering if I could silylate and protect only alcoholic OH not the carboxylic OH. As I looked in the literature, it seems alcoholic OH is more reactive than carboxylic OH for silylation.
Are there any considerations using silylation and coupling reagents together? And which reagent do you recommend for silylation?
Thanks
I always liked bis(TMS)acetamide. No solvent needed, just heat the substrate in excess reagent. You will get TMS esters of the carboxylates, which are rapidly hydrolyzed with an aqueous workup.
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