Preparation and synthetic application of partially protected brassinosteroids

Synthesis of brassinosteroids with a keto group in the side chain

“…11:9) to give the acetonide 9 (150 mg, 62%) as an oil. The physical and spectral data were identical to those previously reported for this compound [13]. Variant B: A solution of epibrassinolide (5) (173 mg, 0.36 mmol) and boric acid (25 mg, 0.40 mmol) in THF (2 mL) was stirred at ambient temperature for 1.5 h. The 2,2-dimethoxypropane (0.646 mL, 5.3 mmol) and TsOHÁH 2 O (41 mg, 0.22 mmol) were added and stirring was continued for 1 h. The reaction mixture was treated with pyridine (0.1 mL), and then solvents were evaporated in vacuo.…”

“…The CHCl 3 extract was dried (Na 2 SO 4 ) and evaporated to give carbonate 7 (130 mg, 78%) as white crystals. 13 Variant A: A mixture of carbonate 7 (250 mg, 0.49 mmol), 2,2-dimethoxypropane (0.31 mL, 2.5 mmol), TsOH (5 mg) and THF (2 mL) was stirred at room temperature for 45 min. Then Et 3 N (0.3 mL) was added, and solvents were evaporated under reduced pressure.…”

“…(11) A mixture of (22S,23S)-22,23-dihydroxy-3a,5-cyclo-5a-stigmastan-6-one (10) (200 mg, 0.45 mmol, prepared according to [14]), boric acid (30 mg, 0.48 mmol) and MeOH (7 mL) was stirred at room temperature for 24 h. Then water (20 mL) was added, the precipitate was filtered off and dried by oil pump vacuum for 3 h to give ester 11 (0.15 g, 70%). 1 13 A solution of Br 2 (72 lL, 2.8 mmol) in CH 2 Cl 2 (1.3 mL) was added dropwise to a solution of acetonide 9 (357 mg, 0.69 mmol) and (Bu 3 Sn) 2 O (0.46 mL, 0.89 mmol) in CH 2 Cl 2 (2.6 mL). After stirring at room temperature for 20 min, the reaction solution was successively treated with saturated Na 2 SO 3 and NaHCO 3 .…”

Synthesis, crystal structure and NMR investigation of a new type of cyclic steroidal dimer based on brassinosteroids

“…It is known that stability of boronic esters varies in a very broad interval [11]. A good example is 2a,3a;22,23-diboronic ester of epibrassinolide [12]. 2a,3a-diol boronic moiety in this compound is not stable during TLC run, whereas cyclodimer 3 showed no signs of decomposition upon work-up and column chromatography.…”

Design and studies of novel polyoxysterol-based porphyrin conjugates

“…There was an evident concern to manage two diol functions present in the molecules of 20E and EBl. However, preliminary experience with 24-epibrassinolide methylboronates [46] suggested a possibility to achieve a selective formation of the side-chain functionalized conjugates.…”