Just thought I'd throw this out there. As part of a total synthesis project, I have serine methyl ester as the hydrochloride salt, and as I would
like to do a PMB protection which forms H2O I would like to convert the methyl ester to the freebase, so the PMB protection can be done in toluene and
a dean stark.
I have tried washing with Na2CO3 and then extracting with DCM, but the freebase is not present in the organic layer upon removal of the DCM under
reduced pressure.
Very stangekristofvagyok - 1-3-2013 at 11:38
Dissolve it in chloroform, or DCM, EtAc or any solvent what is available and add triethylamine. The TEA.HCl could be filtered out and you can get the
base easily.
Important to note that if chloroform is used, a little TEA.HCl will left dissolved next to your amino-acid, ester, so it's a good point to mash with a
LITTLE cc.Na2SO4 soln of water.
Also other bases could be used, I have made a similar thing TMEDA in CHCl3 not long ago... Nicodem - 1-3-2013 at 12:06
I have tried washing with Na2CO3 and then extracting with DCM, but the freebase is not present in the organic layer upon removal of the DCM under
reduced pressure.
Very stange
What do you mean strange? The serine methyl ester has the calculated logP(octanol/water) of -1.26 (by ACDlabs). I would find it strange if you would
be left with a relevant amount after solvent removal.
Important to note that if chloroform is used, a little TEA.HCl will left dissolved next to your amino-acid, ester, so it's a good point to mash with a
LITTLE cc.Na2SO4 soln of water.
Actually, triethylamine hydrochloride is quite soluble in chloroform and dichloromethane.
To get the free amino ester, you can try stirring the methanolic solution over Na2CO3 for 15 min, then filter and rotavap. If you are lucky, the free
base will not decompose that fast and you might be able to transfer it to toluene. Obviously though, it will likely decompose upon heating thereon.
What is the reference that claims such a benzylation to the PMB protected amino ester?
PS: Open threads without references only in the Beginnings section. Please read the forum guidelines for more information.peyotepacman - 4-3-2013 at 08:04
Thanks for the replies. It's been a while since I did any organic chemistry, so I need a few nudges. The LogP value clears up a lot of questions.
I can get the PMB on by doing the reaction in MeOH using Et3N, and reducing the imine with H2, but yeilds are 60% ish after a rather long column as I
can't wash with H2O.
