Gibberellic acids

The plant growth regulator gibberellic acid was synthesized along the lines of the plan discussed in Section 6.4 of Part One. 

A second route to the key tricyclic intermediate A for the synthesis of gibberellic acid was also developed (Ref. 8)  

NajCOj, THE (until complete removal of sulfUr contaminant) 

The synthesis of the tricyclic intermediate A was further improved by the development of a short and stereocontrolled synthesis of compound B (Ref. 9)  

Retrosynthetic analysis of antheridic acid produced a totally different plan of synthesis from that which had been employed for the structurally related target gibberellic acid. The synthesis of antheridic acid, which included a number of novel steps, allowed definitive assignment of structure and revised stereochemistry at C(3). 

Compound A possesses the structure originally proposed for the methyl ester of AAn (see K. Nakanishi, M. Endo, U. Naf, and L. F. Johnson, J. Am. Chem. Soc. 1971, 93, 5579). However, the 270-Mhz 1H NMR spectrum of synthetic A was different from that reported for AAn methyl ester with respect to the protons at C(3) and C(5). Therefore, the 3a-alcohol, compound B, was synthesized as shown below. 

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A 2-methoxyethoxymethyl ether was used to protect one phenol group during a total synthesis of gibberellic acid. 

Phenacyl esters can be prepared from the phenacyl bromide, a carboxylic acid, and potassium fluoride as base. These phenacyl esters can be cleaved by irradiation (313 nm, dioxane or EtOH, 20°, 6 h, 80-95 % yield, R = amino acids > 300 nm, 30°, 8 h, R = a gibberellic acid, 36-62% yield ). Another phenacyl derivative, RC02CH(C0C6H5)C6H3 3,5-(0CH3)2, cleaved by irradiation, has also been reported. ... 

Estrone (54, Chart 6) contains a full retron for the o-quinonemethide-Diels-Alder transform which can be directly applied to give 55. This situation, in which the Diels-Alder transform is used early in the retrosynthetic analysis, contrasts with the case of ibogamine (above), or, for example, gibberellic acid (section 6.4), and a Diels-Alder pathway is relatively easy to find and to evaluate. As indicated in Chart 6, retrosynthetic conversion of estrone to 55 produces an intermediate which is subject to further rapid simplification. This general synthetic approach has successfully been applied to estrone and various analogs. ... 

Still another synthetic route to gibberellic acid has been developed which differs from those above in the transforms used to disconnect the various rings, but which also depends on the initial disconnection of ring A (using aldol and carbonyl addition transforms). ... 

Scheme 6. Corey s synthesis of gibberellic acid GA3 (22) employing the Upjohn catalytic dihydroxylation procedure.

Gibberellic acid (Figure 16) complexes of [Bu2Sn(IV)] , [BusSnflV)], and [PhsSndV)] have been prepared. The monomeric [BusSndV)]" derivative has the strongest antitumor activity. ... 

M. E. Brown, R. M. Jack.son, and S. K. Burlingham, Effects produced on tomato plants by seed or root treatment with gibberellic acid and indol-3yl-acetic acid. Journal of Experimental Botany /9 544 (1968). 

In a synthesis of gibberellic acid, a diene and quinone, both with oxygen-substituted side chains, gave the initial intermediate. Later in the synthesis, an intramolecular D-A reaction was used to construct the A-ring. 

A variety of chemicals may be leached from the aerial portions of plants by rainwater or by fog-drip (16) including organic acids, sugars, amino acids, pectic substances, gibberellic acids, terpenoids, alkaloids, and phenolic compounds. Colton and Einhellig (17) suggested that leaf leachates of velvetleaf (Abutilon theophrasti) may be inhibitory to soybean (Glycine maxT We have recently discovered specialized hairs on the stems of velvetleaf plants which exude toxic chemicals. 

Effect of Solstitialin and Gibberellic Acid on Sago Pondweed (Potamogeton pectinatus)a... 

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