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Solutions for Carbohydrates and Nucleic Acids CH2OH H OH H OH CHO HO H OHH OHH CHO OHH OHH CH2OH OHH Ph NHCH3H CH3 CH2OH H OH HO H CHO HO H H OH HHO CHO OHH HHO CH2OH CH3 H3CHN H Ph HO H CH2OH H OH HO H CHO HO H HO H OHH Ph HH3CHN CH3 O H OH H H OH H HO HO H CH2OH HHO HHO CHO OHH OHH CH2OH CH3 H NHCH3 Ph HO H 7 (a) continued: stereochemical view 1 2 3 4 (b) Ephedrine is the erythro diastereomer, represented by structures 1 and 2. Structures 3 and 4 represent pseudoephedrine, the threo diastereomer. (c) The Fischer-Rosanoff convention assigns D and L to the configuration of the asymmetric carbon at the bottom of the Fischer projection. Structure 1 is D-ephedrine; structure 2 is L-ephedrine; structure 3 is L- pseudoephedrine; and structure 4 is D-pseudoephedrine. (d) It is not possible to determine which is the (+) or (–) isomer of any compound just by looking at the structure. The only compound that has a direct correlation between the direction of optical rotation and its D or L designation is glyceraldehyde, about which the D and L system was designed. For all other compounds, optical rotation can only be determined by measurement in a polarimeter. 33 2 inversion at bottom chiral center ⇒ L-series sugar4 8 (a) (b) (c) D-allose D-talose D-idose (d) D-xylose L-arabinose 6 6 5 5 44 3 3 2 2 1 1 9 D-mannose rotate 599