DIOXIMES OF CORTISOL, STEREOISOMER IDENTIFICATION BY C-13 NUCLEAR-MAGNETIC-RESONANCE

Treatment of cortisol with hydroxylamine hydrochloride yields mainly two dioximes, the EE and ZE stereoisomers. In the EE isomer, the hydroxyl at C-3 oxime, is oriented towards C-2 causing a large upfield shift on this carbon which is attributed to steric compression caused by the hydroxyl. In the ZE isomer, the hydroxyl points toward C-4. Here, steric compression affects carbons C-4 to C-6 causing a diamagnetic shift. The oxime at C-20 assumes only the E-configuration because of steric hydrance.