CFTA, a new efficient agent for determination of absolute configurations of chiral secondary alcohols

The origin of an unusually large 19F chemical shift difference between the diastereomeric α‐cyano‐α‐fluoro‐p‐tolylacetic acid (CFTA) esters of 3′,4′,5,7‐tetra‐O‐methylepicatechin

“…Thus, a very reliable determination of the stereochemistry of chiral alcohols and amines is allowed through simple 1 H NMR spectroscopic analyses. [7][8][9] In addition, a good correlation was observed between the 19 F NMR chemical shift differences (Dd F ) and absolute configurations of substrate moieties for a series of diastereomeric CFTA esters 7 of chiral secondary alcohols and of CFTA amides 10 of a-amino esters. Although the correlation between Dd F and absolute configurations of alcohol and amine moieties in diastereomeric esters and amides has been examined for some fluorine-containing CDAs, 1,11,12 the relation observed between Dd F and absolute configurations was not simple, and a convincing explanation for the origin of Dd F has not been reported so far.…”

“…, the ester of (S)-acid with (R)-alcohol is designated SR and that of (R)-acid with (R)-alcohol is designated RR) 7 between the diastereomeric (R)-and (S)-CFTA esters of epicatechin, 4a and 4b, is shown in Figure 1 together 7,8 are positive and those on the right side of the plane are negative. This result correctly indicates that the absolute configuration at C 3 is R and strongly suggests that the conformation with an all synperiplanar (sp) FÀ ÀCaÀ ÀC(¼ ¼O) À ÀOÀ ÀCÀ ÀH arrangement is preferred for both 4a and 4b.…”

Synthesis of enantiomers of exo‐2‐norbornyl‐N‐n‐butylcarbamate and endo‐2‐norbornyl‐N‐n‐butylcarbamate for stereoselective inhibition of acetylcholinesterase

“…3 and Table 1). [35][36][37] In a NMR tube, (R)-(1)-exo-2-norborneol (5 mM) was condensed with the Mosher's chiral derivatizing agent (S)-(1)-a-methoxy-a-trifluoromethyl-phenylacetyl chloride 35 (5 mM) in CDCl 3 in the presence of pyridine (5 mM) at 258C for 24 h (Scheme 3). The fluorine chemical shifts at 273.948 and 274.113 ppm with the integration ratio of 9/1 were assigned to be the fluorine atoms of (2R)-and (2S)-exo-norbornyl-(S)-a-methoxy-a-trifluoromethylphenyl acetates, respectively (Scheme 3) (Fig.…”

Stereoselective inhibition of butyrylcholinesterase by enantiomers ofexo- andendo-2-norbornyl-N-n-butylcarbamates

“…values of (R)-(+)-exoand (S)-(-)-exo-2-norborneols from the resolutions were calculated to be 80 and 84%, respectively, from the 19 F-NMR spectra of their Mosher's esters, according to the following [39][40][41] ( Figure 3 and Table 1). In an NMR tube, the condensation reaction of (R) (2S)-exo-norbornyl-(S)--methoxy--trifluoromethylphenyl acetates, respectively (Scheme 3) ( Figure 3A).…”

“…Duplicate sets of data were collected for each inhibitor concentration. [34][35][36][37][38] and the 19 F-NMR spectra of their Mosher's ester derivatives [39][40][41] (Table 1 and Scheme 3).…”