Hula-Twist Racemization of the 1,2-Bis ethoxycarbonyl ethyl Group

2 Hula- Twist Racemization of the 1,2-Bis(ethoxycarbonyl) ethyl Group 

The size of the reaction cavity plays an important role in the first mode of racemization as observed in the 1-ce complex crystals. The cavities for the bece groups 

For the bace complex crystals, the volumes of the reaction cavities were calculated to be 68.3 and 68.0 A, respectively. The volumes of cavities are too small for the bace group to be racemized without destroying the crystalline lattice. 

Arai and Ohgo proposed a mechanism of 1,2-hydrogen migration from the 

This motion is very similar to the hula-twist motion, a model of the cis-trans isomerization of retinylidene chromophore in rhodopsin as shown in Fig. 4.24 [16-19]. Such a motion is believed to be very suitable for isomerization in a highly restricted environment, for example, in enzymatic reactions in a Uving cell or 

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