A reduced pheromaxein fraction was run on SDS/PAGE ensuring that ≈ 3–5 µg pheromaxein C was present. The gel was stained with quick Coomassie blue stain [% (w/v) Coomassie blue; 20% (v/v) methanol; % (v/v) acetic acid] for 20 min and destained in 30% (v/v) methanol until the band could be visualized. Pheromaxein C was excised from the gel using a sharp scalpel blade. A similarly sized piece was removed from a blank section of the gel to act as a negative control. To carry out shrinkage and dehydration, the gel pieces were covered with 25 m m Tris/HCl (pH )/50% (v/v) acetonitrile, and incubated at 30 °C with shaking for 45 min. The supernatant was discarded and the above wash step repeated. The gel pieces were dried thoroughly by standing them on their ends on a glass plate, and passing over a gentle stream of nitrogen until brittle.
Example 8 ml. dimethylsulfoxide, g. sodium hydride, and g. trimethyloxosulfonium iodide are stirred at room temperature until gas development stops (about 40 minutes). Then, there are added g. A -5iz-androstene- 3,17-dione-3-ethylene ketal (. 1485-1495 C.; prepared from A -5-a-androstene-3fi-ol-17-one-17-ethylene ketal (Chem. Listy, 51, 1885 (1957), and JACS 82 (1960) 32-09) by oxidation of the OH group in position 3, ketalization of the resulting 3-keto group, and partial ketal dissociation with p-toluenesulfonic acid in aqueous acetone). The mixture is stirred 90 minutes at room temperature, precipitated with ice water, and the crude product is purified by chromatography. There are obtained g. 15,1Gfi-methylene-Sa-androstane-3,17-dione 3 ethylene ketal of melting point -159" C. (from diisopropyl ether).