I need advice on how to make acetylation then bromination for galactose.
I ask in general if i can obtain galactose pentaacetate from galactose by acetylation i need the method or any paper guide me then galactose pentaacetate will be brominated also i need the method or any paper guide me
Hi,
this is standard carbohydrate chemistry. I'm quite sure you can find procedures for both steps in many books on carbohydrate chemistry or even online! Nevertheless, I'll write a procedure.
The acetylaton step can be done by adding a huge excess Acetic anhydride (dropwise) to your sugar in anhydrous pyridine. Stir at room temperature over night and/or follow your reaction by TLC to see when the starting material has disappeared. Concentrate your mixture under reduced pressure and co-evaporate several times with Toluene to remove (traces of) Pyridine. Purify the residue with column chromatography (e.g., Cyclohexane:EtOAc 6:4). This should give you 95-97 % yield of your alfa/beta product in 3:1 ratio.
The reaction to form the (alfa) glycosyl bromide can be done using HBr in AcOH (33 %) at 0 degrees Celsius. Then, stir at room temperature for 2 hours and extract to dichloromethane, wash the solution carefully with ice cold H2O and dry the organic layer with MgSO4. After evaporation of dichloromethane under vacuum you should be able to obtain the desired bromoanalogue in very high yield (~98 %).
Regards,
JR
Firstly I'm a new Researcher need to every scientist help me
secondly thanks Dr Jan-Erik Raitanen Thank you for your presentation interesting
i will be grateful if u provide me the reference for acquiring more skills
If you are specifically interested in synthetic carbohydrate chemistry, you could look up
"Carbohydrate Chemistry: 99 Oxford Chemistry Primers" (Oxford University Press, 2002) by Benjamin G. Davis and Anthony J. Fairbanks.
It's short but detailed and "up to date" despite coming out for more than 10 years ago. The methods in carbohydrate chemistry were established a long time ago and not much has changed. The primer brings up many important things: structure (open chain and ring) and nomenclature of carbohydrates, the anomeric effect, neighbouring group participation, protective groups ( the corner stone of synthetic carbohydrate chemistry! e.g., protecting or deprotecting selectively), glycosyl donors and acceptors in di/tri/tetra/etc saccharide synthesis and so on. You might be able to find this primer at the library at your university.
Regards,
JR
thanks Dr my interest is medicinal chemistry to establish prodrugs .
galctose pentacete is commercial(Aldrich) but you can simply use standard Ac2O, Py procedure.
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