Structural Revision of the Acetal Intermediates in Brassinolide Synthesis

Facile Syntheses of Brassinosteroids: Brassinolide, Castasterone, Teasterone and Typhasterol

“…NaHC03, dried over MgS04 and concentrated in vacuo to give Ib (458 mg), mp 255-257°C (from AcOEt-MeOH). The IH-NMR, IR and EI/MS spectra were identical with our previous synthesized castasterone (lb (10). 3N-HzS04 (1.34ml) was added to a solution of 2b (1.03g) in AcOH (20ml).…”

“…The acetonide 8b was converted into brassinolide (la) in a similar manner to that described from tetraacetylcastasterone. 5 ) The cydoketone 2b was converted into a 3f3-acetate (10) in a similar manner to that described for 3f3-acetoxy-5oc-ergost-22-en-6-one. 6 ) A small amount -of a 3f3-alcohol compound was produced in the reaction, so the product was acetylated and then purified.…”

“…The IH-NMR, IR and EI/MS spectra were identical with our provious synthesized sample. 10 ) (22R,23R,24S)-2rt.,3rt.,22,23-Tetrahydroxy-5rt.-ergostan-6-one (castasterone, Ib). A ION-NaOH aqueous solution (1.0ml) was added to a solution of 8b (589mg) in methanol (50ml).…”

“…The residue was dissolved in pyridine (10ml), before acetic anhydride (1.0ml) and 4-(N,N-dimethylamino)pyridine (IOmg) were added to the solution. The mixture was stirred at room temperature for 2 hr, and working-up gave crude 10, which was chromatographed on SiOz with AcOEt-benzene = I : 8 as the eluant to give crystals of 10 (13). Silver acetate (0.79 g) was added to a solution of 12 (1.42 g) in acetic acid (24 ml).…”

Efficient Synthesis of (22R,23R,24S)-22,23-Isopropylidenedioxy-5α-ergost-2-en-6-one, a Key Intermediate in the Preparation of Brassinolide

“…The epoxide 8b (4.31 g) was converted, in a similar manner to that described for 9c, into amorphous 9b (2.26 g), enabling 0.61 g of 8b to be recovered. 13. Dioxane (100ml), water (40ml) and p-TsOH (0.1 g) were added to 9b (2.00 g), and the solution was stirred and was heated under reflux for 1 hr.…”