ABSOLUTE CONFIGURATIONS BY X-RAY AND 'H NMR 703 (a) CH3 (b) =g500-11600 9S 100 mg injected +16 (张8 njec -OH =173 injec (S1R.3R.4--66 (R:IR.3R.4S)-(-)-66b.X-ray RI CHgo. 产贤院 (S:1R,3R.4S-(-→66 (⑤-(+3 Achiraahacuin-) OH o (R:1R.3R4S(-→66 (R-(-3 R8杰罗 stereostructure of menthol MaNP ester Chirality DOI1.12/chrcarried out as shown in Figure 17. In general, for enantio￾resolution of carboxylic acids, chiral synthetic amines or alkaloids have been used. However, we have adopted the following novel strategy to use chiral alcohols; chiral alco￾hols are condensed with racemic acid 3 and the diastereo￾meric esters formed are separated by HPLC on silica gel. The separated esters are then hydrolyzed to yield both enantiomers of the desired carboxylic acids 3. As a chiral alcohol, naturally occurring (1R,2S,5R)-(2)- menthol was selected and esterified with racemic acid (6)-3. It was surprising that diastereomeric esters 66a Fig. 18. HPLC separation of MaNP acid menthol esters (S;1R,3R,4S)- (2)-66a and (R;1R,3R,4S)-(2)-66b56: (a) analytical HPLC; (b) preparative HPLC. Fig. 19. The X-ray stereostructure of menthol MaNP ester (R;1R,3R,4S)-(2)-66b. 22 Fig. 17. Preparation of enantiopure MaNP acids (S)-(1)-3 and (R)- (2)-3. 56 ABSOLUTE CONFIGURATIONS BY X-RAY AND 703 1 H NMR Chirality DOI 10.1002/chir