The readily accessible pregna-5,16-dien-3/l-ol-20-one ( I ) was transformed into 3/l-acetoxy-pregna-5,I7-dien-20-isopropoxy-16one ( 9). This compound was labelled by base-catalyzed isotopic exchange and then reconverted into labelled pregna-5,16-dien-3/l-01-20-one (13). Hydrogenation of this last one furnished the title compound (14). The labelling extent in the 15a,15/l and 21 positions M ~U S determined by combined chemical and microbiological methods.
In the course of an investigation on the biosynthesis of cardenolides (l we needed pregn-5-en-3P-ol-20-one labelled with tritium in the 15u and ISP positions. This compound had to be incorporated into cardenolides by Digitalis lanata plants with the aim of verifying the hypothesis according to which the introduction of the 14P-hydroxyl on the cardenolide skeleton occurs through a AI4 (15)-pregnane-type precursor. Moreover the above compound can be very useful in biosynthetic and metabolic studies in the steroid field.
Accordingly we synthesized 15a, 15p,21,21 ,21-3H,-pregn-5-en-3P-ol-20one (14).
The introduction of the label in the 15 positions is not a simple matter : attempts to prepare a C-15 labelled pregnan-20-one by acid-catalyzed ( 2 ) or base-catalyzed (3) exchange of 5u-pregn-16-en-20-0ne produced only the 21,21 ,21-d3-label1ed analog.
However we succeeded in introducing the label in the 15 position by exchange of pregna-5,16-dien-3P-ol-20-one (1) with sodium deuteroxide in deuterium oxide-dioxane under drastic conditions (when 160 rng of (1) were dissolved in 12 ml of dioxane and 5 ml of 0.4 N NaOD in D,O and kept at I 50° under nitrogen atmosphere in a sealed tube for 260 hr, mass-spectrometric analysis revealed a small introduction of deuterium at (2-15) (Scheme 1).
* During preliminary experiments, use of methanol instead of isopropyl alcohol resulted in complete conversion of the enol-ether (9) into the dione (8); the quantity of water in the isopropyl alcohol-water mixture reaches a critical values at lo%, beyond which total transformation of the enol-ether into the corresponding dione occurs.