Probably F-19 NMR could be used to monitor the progress of the reaction between MTP-Bt and an amino acid, which forms a Mosher amide. We plan to use one more equivalent of base than was specified in the original protocol, because our amino acids are in the form of a hydrochloride salt and the original protocol used amino acids that are presumably not hydrochloride salts. Katritzki and Collaborators did not perform a column afterwards; they perform an extraction (protocol below). I have occasionally purified molecules bearing carboxylic acid groups over silica, but my recollection is that the solvent was quite polar. We don't plan to run a column; we don't have much experience working on such a small scale, and we don't have a reason to believe that a column is necessary.
General Procedure for Synthesis of 2a-d: Benzotriazol-1-yl-
3,3,3-trifluoro-2-methoxy-2-phenylpropan-1-one (0.2 g, 0.6 mmol)
was added to amino acid, di-, or tripeptide (0.6 mmol) in CH33CN/
water (2:1, 15 mL). Triethyl amine (0.12 mL, 0.9 mmol) was added
dropwise to the above reaction mixture and stirred at rt for 12 h.
The volatiles were removed, and the residue was added to
ethylacetate (50 mL) and washed with 4 N HCl (10 mL); the organic
layer was separated and dried over Na2SO4, filtered, and evaporated
to give the products 2a-d.