From: Sandra Bartoli (S.BARTOLI$##$soton.ac.uk)
Date: Mon Feb 09 2004 - 10:21:06 EST
You can try and use sonication and NaHCO3 as a base, but do not use the chloride, use the anhydride.
1 eq. H-Glu-OH
1 eq. anhydride
4 eq. NaHCO3
Solvent: MeOH or water, strange but true.
Sonication for 4-5 h.
It works very well with acetic and boc anhydride so you might try it, it is a very simple procedure.
Otherwise you might try using a different base like DMAP or NEt3, as you suggested. I think NaOH is not the best choice of base for the labile benzoyl group, but this is my opinion.
----- Original Message -----
From: Devin Pantess
Sent: Sunday, February 08, 2004 6:14 AM
Subject: ORGLIST:N-(benzoyl)-L-glutamic acid synthesis
I'm working on the synthesis of N-protected amino acids, but I cannot get this reaction to work:
1 eq. L-glutamic acid
1 eq. Benzoyl chloride
The rxn is run under Schotten-Baumann conditions. 1.0g L-glutamic acid is dissolved in 10mL NaOH, iced, and the Benzoyl chloride is added dropwise over 1hr with a syringe. pH is monitored and adjusted >12 when necessary with 2M NaOH. After acid chloride is in, stir 2h at room temp. Re-ice, and acidify to pH~2. Collect product by vacuum filtration and recrystallize from 95% EtOH.
Well, the problem is I got a very low yield (90.5 mg crude, 19.5 mg product after recrystallizing) what can I do to improve this? The reported yield for this procedure was around 89%. My product doesn't have a great NMR spectrum, and I don't see the peaks for L-glutamic acid, just those from benzoic acid!
I'm really getting frustrated with what would seem to be simple chemistry. I am going to run the rxn in pyridine/DMAP next time I think.
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