Gibberellins (named GA1 through GAn in order of discovery,

Chapter 22, Problem 22.12

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Gibberellins (named GA1 through GAn in order of discovery, over 120 are known) are plant hormones that regulate growth and influence various developmental processes, such as germination, flowering, etc. The modified gibberellin exo-16,17-dihydro-GA5-13-acetate (1) has considerable promise in reducing the risk of lodging (harmful to a plants growth) in cereal crops such as corn and wheat. O OC OAc CO2H H H 1 When developing a new drug for plant or human use, it is often important to introduce a radiolabel, or an isotope, into the structure so it can be traced as it does its job, and subsequently the metabolites (smaller fragments of the original compound formed as a molecule is metabolized) can be tested for toxicity to the host or environment. For the purpose of compound 1, C3 will be labeled with 14C (illustrated with an asterisk, *), and a key step in the synthesis of this labeled compound involves an intramolecular aldol-type reaction to form a ring (Can. J. Chem. 2004, 82, 293300). Draw a detailed, stepwise mechanism for the transformation of aldehyde 2 to alcohol 3. O C H OAc CO2H H H 2 OHC O 1) 2) HCl KO OK O * O OC OAc CO2H H H 3 3-( HO * 14C)-1 H2O * = 14C-labeled carbon