Synthesis of gibberellins

Riboflavin is produced by Clostridium, Ascomycetes and Candida species. The yield can be as high as 5 g 1 1 after 7 days 60). Gibberella fujikuroi is utilized for the synthesis of gibberellins, a group of plant hormones used for plant growth promotion. Glucose, molasses, lipid (corn oil) are usually used as carbon sources. Vitamin B12 may also be synthesized from alcohols and hydrocarbons. 

Irradiation of the a -unsaturated ketone derived by manganese dioxide oxidation of methyl gibberellate, affords, in the solid state, a dimer in which addition of the unsaturated ketone across the terminal methylene group has occurred. Photolysis in solution leads to addition of the solvent to the unsaturated ketone. Some interest has centred on the partial synthesis of gibberellin Ajg (105), whose total synthesis was reported earlier. Details of the conversion of gibberellin A g into some 5-lactones related to gibberellin A15, and on the partial synthesis of gibberellin Ajg nor-ketone from 7-hydroxykaurenolide, reported... 

The conversion of the tricyclic keto-ester (112) via the bromohydrin (113) into methyl 7,16-dioxo-17-norkauran-19-oate (114) constitutes a formal total synthesis of gibberellin Aj2. 

The gibberellin plant hormones continue to attract synthetic attention. The total synthesis of gibberellin A4 (101) by a more efficient route has been reported,176 and a major achievement has been the total synthesis of gibberellin Ax (102) and... 

The diketo ester D was then converted to B. In the course of this work, both C and D could be provided by degradation of commercially available gibberellin A3. The relay synthesis of gibberellin A4 was completed in December 1967 just before Professor Yabuta s 80th birthday. Since the conversion of... 

Figure 2.8 Partial synthesis of gibberellin C. Modified by permission of Shokabo Publishing Co., Ltd...

A number of research groups worked on the total synthesis of gibberellins. The works of W. Nagata, E.J. Corey and F.N. Mander were reviewed by Mander.37 Other notable syntheses were Nagaoka s work on ( )-gibberellin A338 and Toyota and Ihara s work on gibberellin Ai2.39... 

The procedure was used successfully in the synthesis of gibberellin C from the dienone group (7).4 The ketone group at C8 was protected by ketalization, carboxylation was conducted by the Robinson-Cornforth method, the resulting acid esterified with diazomethane, and finally the diketo diester (8) was obtained after... 

A partial synthesis of gibberellin Ajj nor-ketone from 7-hydroxykaurenolide has been described. The key stage in this synthesis is the activation of the C-20 methyl group by photolysis of a C-19 amide (173). 

Thus a common intermediate (140) for the synthesis of gibberellins Aj5 (135) and A37 (141) was derived from (136) as shown in Scheme 23. From this intermediate (140), gibberellins A15 (135) and A37 (141) were efficiently prepared by reduction, Wittig reaction, and demethylation or by Wittig reaction, dethioacetalization, reduction, and demethylation, respectively, as shown in Scheme 24 108). 

Sitton D, Richmond A, Vaadia Y (1967) On the synthesis of gibberellins in roots. Phytochemistry 6 1101-1105... 

Cross, B. E., and I. L. Gatfield New Metabolites of Gibberella fujikuroi. Part XVII. The Partial Synthesis of Gibberellin Ais Norketone from 7-Hydroxykaurenolide. J. Chem. Soc. (C) 1971,1539. 

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