Gibberellin 2 -hydroxylation

Gibberellins Growth, complex 5-ring hydroxylated alicycle. Requires iron containing enzyme for synthesis... 

Gibberellin A5 (C H Os) has a melting point of 260-61° and forms a methyl ester (m.p. 190-91°). The infrared spectra of Nujol mulls of the acid and ester (see Table II) show the presence of alcoholic hydroxyl, hydroxyl of carboxylic acid, unconjugated five-ring lactone, carboxyl (or ester) carbonyl, exocyclic methylene group, and a cis-disubstituted double bond. Catalytic hydrogenation of the methyl ester confirmed the presence of two double bonds. 

Gibberellin A8 (XI) (m.p. 210-15°) analyzes as C19H2407—i.e., gibberellin Ai with an additional hydroxyl. It gives a methyl ester (XIII) which exists in dimorphic forms (m.p. 221-24° and 231-36°) (Figure 3). 

The position of the second hydroxyl group in gibberellin Ae is not yet known and we are actively engaged in locating it. 

Table IV shows the Rf values for all the gibberellins except A2, on paper and in four different solvent systems. The gibberellins are arranged in order of increasing mobility (in fact, in increasing number of hydroxyl groups). The relative mobilities (R.M.) in brackets are given to compare with relative mobilities derived from published Rf values for unidentified gibberellin-like materials.

Finally, the very low R.M. values of 20 to 40, reported by Murakami (13, 14) for active zones of extracts of seed of several legumes, suggest a heavily hydroxylated gibberellin. 

Weis, C., Phinney, B.O. "Fungal products. Part XVII. Microbiological hydroxylation of gibberellin Ag and its methyl esters." J.C.S. Perkin Trans. 1976, 1, I78-I83. 

Giberellin A synthetase (plant) mononuclear iron gibberellin formation Substrate carbanion and iron bound hydroxyl 3.2.2. 

Figure 5.8 Examples of oxidative secondary transformations in terpenoid biosynthesis, (a) Hydroxylation of epi-aristolochene at the 3-position by a cytochrome P450-dependent terpene hydroxylase in Capsicum annuum (Hoshino et ai, 1995). (b) Conversion of GA12 to CA9 by a 2-oxoglutarate-dependent dioxygenase involved in gibberellin biosynthesis.

The introduction of methyl substituents onto 13-hydroxylated gibberellins was... 

Osmium tetroxide [1, 759-764, before references]. On oxidation of gibberellin A14 dimethyl ester (1) with osmium tetroxide in pyridine, followed by sodium periodate, Cross13 obtained the expected norketone (2) as the major product but also isolated a small quantity of (3), a product of further oxidation of the secondary hydroxyl group present. A footnote states that several similar examples of the oxidation of secondary alcohols by osmium tetroxide have been encountered. ... 

---