[Babcock_Hall]

I will try to keep my comments about the synthetic questions separate from those that deal with the stereochemical issues of the final product.  When we made and purified the adduct between the Mosher acid and HBt (MTPA-Bt), the TLC of the first peak from the silica column had two spots, one  stronger spot near 0.7 and one weaker spot near the baseline, about where free BtH standard had appeared.  The only interpretation that I could come up with was that a small fraction of the material spotted onto the TLC plate decomposed into some free BtH and either the Mosher acid or a derivative of the Mosher acid, but I am far from certain.

A very preliminary look at the H-1 NMR of the purified MTPA-Bt suggested that we had the correct product.  We obtained a F-19 spectrum at the same time, and we saw one strong peak near -71.3 ppm and one small peak at -79.9.  The 2007 J Org Chem paper did not report a value; therefore, we cannot compare our results with theirs.  We elected to go ahead with the reaction between MTPA-Bt our amino acid, and we will perform the extraction tomorrow.

[Babcock_Hall]

When I looked at the data for two diastereomers of phenylalanine coupled with MTPA (the Mosher acid) presented in the 2007 J Org Chem paper by Katritzki and collaborators, I saw differences in the H-1 chemical shifts for the HCα (0.1 ppm) and H₂Cβ (less than 0.1 ppm) of phenylalanine, as they indicated.  I observed a difference of about 0.2 ppm for H₃CO (this is the methoxyl group on MTPA, the Mosher acid portion of the molecule).  There is also a difference of about 0.4 ppm for the corresponding H₃CO (the carbon of the methoxyl group) in the C-13 spectrum, if I am not mistaken.  This difference was about as large as the difference observed at Cα and larger than the difference observed at Cβ of phenylalanine in the C-13 spectrum.

I found this information in their supplementary material, and I need to check the spectra one more time to make sure that I did not miss something.  I was surprised that the authors did not comment on the differences in chemical shift for H-1 and C-13 spectra in the methoxyl group for the two diastereomers: these differences were as large as or larger than the ones that they did discuss.  I do not know whether other amino acids behave in a similar manner; phenylalanine is one of four amino acids (out of the 20 major amino acids) which has an aromatic or heteroaromatic ring.  The authors also reported a small difference observed by F-19 NMR.

[rolnor]

I made an amide from racemic cis-2-phenyl cyclopropylamine and O-Methylmandelic acid. these diastereomers separated nicely on TLC so we could separate them on a column and cleave the amide with HCl to liberate the two enantiomers of phenylcyclopropyl amine. What I mean by that is that all the peaks in a carbon or proton NMR could well separate in the Mosher amide, this is not surprising to me. It seems OK then, Great!