The enzyme THCA synthase catalyzes the overall conversion of cannabigerolic acid

Question

The enzyme THCA synthase catalyzes the overall conversion of cannabigerolic acid (CBGA) to tetrahydrocannabinolic acid (THCA), a controversial natural product synthesized in the Cannibas plant. The initial catalytic step, starting from CBGA (shown below), involves a deprotonation of a phenolic OH group and a subsequent hydride delivery to the FAD cofactor to generate an intermediate shown in the brackets and the reduced cofactor. The second step involved in THCA synthase (shown below) involves a cyclization to convert the intermediate shown above to the final product, THCA. (a) As discussed several times in CHEM 252 lecture, what is the main thermodynamic driving force for this cyclization step? How many kcal/mol is this driving force worth? (b) Based solely on average bond energies, what is the estimated enthalpy (Delta H) for this cyclization Step?

Explanation / Answer

The cyclization step is fast. The reaction follows diels alder reaction mechanism. The final product has 6membered ring structure. 6 member ring structure is highly stable so as there is no steric hindrance so the thermodynamic energy required will be minimum which is achieved in presence of catalyst

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