The combined physicochemical methods such as ultraviolet, infrared, nuclear magnetic resonance (1) and mass spectroscopy (2) made possible to determine the structures of small quantities of new gibberellins. Optical rotatory dispersion (ORD) and circular dichroism (CD) have been used for the elucidation of stereochemistry of gibberellins after introduction of a ketone at C-7 or C-8 (3).
Here we report CD of some Cl9 gibberellins and their methyl esters as well as some other related compounds at the wave length of 200-500 rnp and its application to the stereochemistry and structural elucidation. CD were measured with a Japan Spectroscopic Model ORD/UV-5 recording polarimeter with CD attachment at room temperature (16-30*C). Sample solutions were prepared by dissolving about 1 mg of the samples in 2 ml of ethanol. Quarz cells with an optical path of 1.0 cm or 0.1 cm were used for measurement.
Gibberellins and their methyl esters have two carbonyl chromophores, a
Y-lactone at C-l and a carboxyl or carbomethoxyl at C-10 in gibbane skeleton, and their ORD showed overlapped Cotton effects due to these two chromophores.
Because of the possible free rotation of the C-10 carboxyl group and its high intensity, theoretical interpretation of the ORD was difficult. However in CD a lactone peak at about 225 rnb was distinguished from the back ground of the carboxyl or the carbomethoxyl peak.