Gibberic acid

Gibberellic acid, C19H2206 (I) is a monobasic acid of pK 4.0. With dilute mineral acid at 20° C. (4) it gives allogibberic acid (II) which with acid at 100° C. yields gibberic acid (III). Structures of these two important degradation products have been conclusively established by us. The evidence has been published in full (II, 26) and it is not dealt with here. 

The carboxyl group is in the same position in both gibberic acid and allogibberic acid, since the methyl esters of each give the methyl ester of gibberic acid on boiling with mineral acid (5, 21). 

Gibberic acid must therefore have the stereochemistry shown in (LVII) [Stork and Newman (32) have reached the same conclusion by similar arguments], and epigibberic acid must be the 4b-epimer of (LVII). 

Infrared spectra of gibberellic acid, gibberellins Au A2, A3, and A4, and aZZo-gibberic acid were kindly furnished by Abbott Laboratories. 

Allogibberic and Gibberic Acids. Both these compounds exhibit weak absorption in the ultraviolet region with maxima at 265 m/. No change in absorption takes place on treatment with hydrochloric acid and hence no interference is caused by either compound. 

The reaction has been exemplified with a variety of aryl-substituted alkynes, but it is interesting to note that a similar reaction with an epoxide-ynamide derivative 81 (Scheme 5.37), catalyzed with AgBF4, yielded the tricyclic central core 82 of gibberic acid. 

Scheme 5.37. Access to the central core of gibberic acid.89...

A1—9 = GibbereUin A1—9 El— 9 = GibbereUin-A1—9, iiiethj lesters GI = Gibberic acid GE = Gibberellenio acid -1 — AG = Allogibberic acid (10) DA = Dicarboxylic acid A... 

Gibberic acid yellow brown 1-3 1 green-blue,... 

ABBREVIATIONS IL = isocitric lyase GA = gibberellic acid G = gibberic acid G> -ME > methyl ester of GA G-ME = methyl ester of G DAP = days after planting DAS = days after spraying 1% = fresh weight ... 

Gibberic acid, T35 Ginkgolides, T40 Glaucanic acid, T58 Glaucanol, T53... 

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