Mosher’s acid derivatives

The (2R,3R,4R) diastereomer results from partial racemization of one or both of the allenylmetal intermediates. This point was confirmed by comparison to authentic material as the (S)-MPA ((S)-(2-methoxy)phenylacetic acid-Mosher s acid) derivative. The optical rotations of these compounds are small, and thus correlation by comparison of [ajp... 

Ethyl trifluoropymvate has been activated in TfOH medium for the hydroxyaUcylation of arenes to give valuable Mosher s acid derivatives in good to excellent yields. Even Selectfluor has been activated in TfOH to effect electrophilic fluorination of arenes including fluorobenzene and chlorobenzene. ... 

Direct trifluoromethylation of a-keto esters give Mosher s acid derivatives (eq 6). ... 

In order to determine the absolute configuration or the enantiomeric excess of a compound containing a hydroxy group, it is often esterified with a pure enantiomer of Mosher s acid (3,3,3-trifluoro-2-methoxy-2-phenylpropanoic acid, MTPA). Which configuration has the ester derived from (S)-l-phenyl-propan-l-ol and (R)-Mosher s acid chloride ... 

One of the most useful methods for determining enantiomeric composition is to derivatize the alcohol with a chiral nonracemic reagent and examine the ratio of resulting diastereomers by gas chromatography (gc). There are many derivatizing agents available, but the most widely used are derivatives of a-methoxy-ot-trifiuoromethylphenyl acetic acid (MTPA, Mosher s acid. 

Bases N-protected amino acids Tartaric acid and derivatives (dibenzoyl- and di-p-toluyltartaric acids) Mandelic acid and derivatives (O-acetylmandelic acid and O-methylmandelic acid) l,l -Binapthylphosphoric acid Camphorsulfonic acid Deoxycholic acid Cyclic phosphoric acid Others (malic acid, lactic acid and derivatives, Mosher s acid, N-derivatized amino acids, etc.) The same reagents as for acids (brucine, quinine, ephedrine, pseudoephedrine and synthetic chiral bases) [32-35] [36-38] [39-40] [41] [42] [29] [43-45]... 

Simple aliphatic enones are also epoxidised with H2O2 using a preformed TFA or CI3CCO2H salt of 9-amino-9-deo gr-ep/-quinine (9-epi-QA), in up to 99% ee. The method was further expanded to a-monosubstituted and a,p-disubstituted enals, using preformed salts of 9-epi-QA with BINOL derived phosphoric acids. Also, epoxidation of 2-cyclopentenones was achieved by using C-2 phenyl-substituted 9-epi-QA in combination with (/ )-Mosher s acid as catalyst. ... 

The use of subtilisin (a protease which is widely used in detergent formulations) as a biocatalyst for the stereospecific hydrolysis of esters is well established [271-273]. Along the same lines, a protease derived from Aspergillus oryzae, which has hitherto mainly been used for cheese processing, has been shown to be particularly useful for the resolution of sterically hindered substrates such as a,a,a-trisubstituted carboxylates [274] (Scheme 2.42). While traditionaT proteases such as subtilisin were plagued by slow reaction rates and low selectivities, the a-tri-fluoromethyl mandelic ester (which constitutes a precursor of a widely used chiral derivatization agent, Mosher s acid [275]) was successfully resolved by Aspergillus oryzae protease [276]. 

Using both computational and experimental techniques, initial studies demonstrated that the position of reaction with a given electrophile was dependent on its size [39]. Related studies, using the prochiral cation derived from decarboxylation of Mosher s acid as a probe, computationally estimated the difference in energy between the adducts formed from Re and Si face attack on this cation as an indicator of stereoinductive potential [42]. 

Investigations on the stereochemistry of chiral semiochemicals may be carried out by (gas) chromatographic separation of stereoisomers using chiral stationary phases, e.g. modified cyclodextrins [32]. Alter natively, formation of diastereomers (e.g. Mosher s ester or derivatives involving lactic acid etc.) may be followed by separation on conventional achiral stationary phases. Assignment of the absolute configuration of the natural product will again need comparison with an authentic (synthetic) reference sample. 

---