Methyl gibberellate

Methyl gibberellate (VIII), the corresponding ketol (IX), and the keto acid methyl ester (X) are oxidized to a,/ -unsaturated ketones (XI) (5). The hydroxyl group is therefore allylic to the ring A double bond. Moreover the Xu. (228 to 229 mfx) of these a,/ -unsaturated ketones is such that the double bond must be disubstituted. A disubstituted double bond, allylic to C-2, can only be placed as shown in structure (VIII). 

This view was abandoned (9) when it was discovered that methyl gibberellate was oxidized to an a,/ -unsaturated ketone with manganese dioxide. 

Epimerization of the 2-hydroxyl does not occur here, since methyl gibberellate and the methyl ester m.p. 174° C. give the same hydrogenolysis acid (see below). 

If the interpretation of the results, shown in Figure 16, is correct and the hydrogenolysis product of methyl gibberellate has a trans ring A/B fusion with the C-10a hydrogen atom -oriented then some recent results of ours (18) provide proof that the lactone is, in fact, -oriented. The argument is as follows (Figure 18) ... 

In fact, the hydrogenolysis product of methyl gibberellate has been shown to possess an equatorial 2-hydroxyl group (LXXIII). This has been established in three ways. 

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... 

Fluorination of an ally lie alcohol. Reaction of methyl gibberellate (1) with this fluoroamine in CH2CI2 at 0° gives (2) and (3) as the major products. ... 

Methyl-a,d-cthylenic sulfoxides, 377 Methyl farncsoate, 448 Methyl fluoride-Antimony penta-fluoride-Sulfur dioxide, 381 Methyl tluorosulfonate, 26, 48, 381-382 Methyl geraniate, 447 Methyl gibberellate, 186 Methyl a-D-glucopyranoside, 26 (3-Methyl glycopyranosides, 437, 438 Methyl 18a-glycyrrhetate, 501... 

H NMR and infrared spectral data of ( )-B, ( )-B methyl ester, and ( )-B methyl ester 3-benzoate were identical with those of AAn and the corresponding derivatives. Mass spectra of the methyl esters of ( )-B and AAn were identical. Chromatographic mobility of ( )-B relative to gibberellic acid (GA3) (as standard) was identical with that reported for AAn. Therefore, this synthesis also proved that antheridium inducing factor, AAn, must be regarded as possessing stereostructure B rather than A as originally supposed. 

Gibberellins which have a saturated ring A undergo epimerization at C-2 with dilute alkali at room temperature, presumably by a reversed aldol mechanism via intermediate (XXXIII) as first suggested by J. W. Comforth (3a). This epimerization has been shown to occur with gibberellin At and its methyl ester (XXXIV), with both C-8 epimeric tetrahydro derivatives of gibberellic acid and... 

Left to right. Untreated gibberellic acid As mixture of gibberellins Ai and As potassium gibbereUate zinc gibberellate methyl ester of gibberellic acid and allogibberic acid... 

Gibb-3-ene-1,10-dicarboxylic acid, 2,4a,7-trihydroxy-1-methyl-8-methylene-, 1,4a-lactone, (1a,2(3,4aa,4bp,10[3)- gibberellic acid 527a, 683a ... 

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