DIVERGENCE BETWEEN THE ENZYME-CATALYZED AND NONCATALYZED SYNTHESIS OF 3-DEHYDROQUINATE

Synthesis of 1-epi-debydroquinate, 9, provided an authentic sample of this material and allowed its identification as a minor product in the noncatalyzed rearrangement of enolpyranose 4a to 3-dehydroquinate, 7 (3-DHQ). None of this isomer was detected in the product of the transformation of DAHP, 1 to 3-DHQ catalyzed by dehydroquinate synthase. This result indicates that the enolpyranose 4a is not released from the enzyme active site prior to rearrangement to 3-DHQ, a possibility suggested previously (Bartlett, P.A.; Satake, K. J. Am. Chem. Sec, 1988, 110, 1628-1630). Enolpyranose 4a was generated in the presence of DHQ synthase; however, the formation of 9 was not diminished, indicating that spontaneous rearrangement is faster than uptake by the enzyme under these conditions. The question remains whether the enzyme takes an active role in catalyzing the rearrangement of 4a to 3-DHQ or simply provides a conformational template to prevent formation of the side product 9,