Concentration chromatography

To a solution of 0.6 g (2.8 mmol) of A -sulfinyl-4-toluenesulfonamide in 10 mL of dry CH,C1Z is added a solution of 2 mmol of aldehyde 1 in 2 mL of dry CI12CI2 at r.t. under argon protection. This mixture is stirred for 2-3 h (exception R1 = /-Pr, 48 h) before 6 mmol of the Grignard reagent is added at 22-30 C. After stirring for another 60 min the reaction is quenched with 50 mL of sat. aq NaCl and twice extracted with HtOAc. The combined extracts are dried over MgS04 and concentrated. Chromatography of the crude product on silica gel (pet. ether/EtOAc 2 1) affords 3a and 3b. 

A mixture of TMSOTf (0.1 mmol, lmol%), allyltrimethylsilane (11.5 mmol) and dichioromethane (1 ml) was cooled to -78 °C, and to this was added benzaldehyde dimethylacetal (10.5 mmol) in dichioromethane (4ml). The resulting mixture was stirred for 6h at —78°C, and then poured into saturated sodium hydrogen carbonate solution (10 ml) and extracted with ether (3 x 20 ml). The combined organic extracts were washed with brine, dried and concentrated. Chromatography on silica gel (1 20 ether hexane) gave 4-pheny]-4-methoxybut-l-ene (9.2mmol, 88%). 

To a stirred solution of 500 mg (1.4 mmol) of 4 in 10 mL of THF at —100 °C is added 1.4 mmol (1 M THF soln) of NaHMDS dropwise. The mixture is stirred for 30 min at —100°C and 500 pi (4.3 mmol, 3 equiv) of 1-bromo-3-methyl-2-butene is added. After stirring for an additional 40 min at —100 the mixture is poured into H20 and extracted with EtOAc. The combined organic extracts are dried over Na3S04 and concentrated, Chromatography (silica gel, CH2C12) gives 6 [R = (CH3)2C = CHCH2] yield 405 mg (68%). 

To a solution of lithium diisopropylamide. prepared from 5.04 mL (35.6 mmol) of diisopropylamine, 22.3 mL (35.6 mmol) of a 1.6 M solution of butyllithium in hexane and 34 mL of THF at —78 C is added dropwise a solution of 5.44 g (32.4 mmol) of ( + )-l-[(R)-ethylsulfinyl]-4-methylbcnzene sulfoxide in 37 mL of THF. A suspension of lithium bromoacetate, prepared from 6.75 mL (48.6 mmol) of bromoacetic acid and 5.15 g (64.84 mmol) of lithium hydride in 50 mL of THF, is added at the same temperature to the yellow solution of the sulfinyl anion. The mixture is stirred for 5 min at — 78 °C, sat. aq NH4C1 is added, and then 10 M hydrochloric acid is added dropwise until the solution reaches pH 2. The mixture is extracted with ethyl acetate, the extracts are concentrated, chromatography of the residue gives the product yield 4.24 g (58%) mp 53-55rC (hexane/diethyl ether). 

Reconstruction experiments showed that methylation efficiency was the same in the solvent used to prepare the standard and that obtained from experimental parfait column concentrates. Chromatography was usually completed within 36 h of final concentration or methylation of a sample. Samples were stored in Teflon-lined crimp-sealed vials at —20 °C. 

Allylation of Pyranosyl Compounds with Allylstannane [19,20]. A solution of the methyl-(p-D-galactopyranosyl chloride) onate 22 (953.5 mg, 1.8 mmol) in 30 mL of dry, oxygen-free THF, was heated to 60°C. To this solution under nitrogen, were added the tributylallyl tin 23 (5.2 mL, 14.7 mmol) and A1BN (15 mg, 0.1 mmol). After 20 h, the solvent was evaporated, and the residue was taken up in 5 mL of acetonitrile. The acetonitrile layer was extracted with 20 mL of n-hexane and then concentrated. Chromatography on silica gel (toluene-acetone, 4 1) afforded the product 24 (889 mg, 93%), containing two anomers. Nuclear magnetic resonance (NMR) spectroscopy showed a ratio of the two anomers of 1.8 1. 

A soln of the acid from hydrolyzed dipeptide 20 (40 mg, 0.115 mmol) in DMF (lmL) was treated with bithiazole 19 (30 mg, 0.088 mmol), HOBt (12 mg, 0.088 mmol), EDC (17.8 mg, 0.093 mmol), and NaH-C03 (30 mg, 0.35 mmol) at 0°C, and the mixture was stirred at 25 °C for 50 h. Brine was added, and the mixture was extracted with EtOAc (5x5 mL). The extracts were washed with sat. aq NaHC03 and brine, dried (MgS04), and concentrated. Chromatography (silica gel, preparative TLC, CH2Cl2/MeCN 2 1 and MeCN/CH2Cl2/MeOH 3 6 0.2) gave the jV-Boc tetrapeptide methyl sulfide yield 50 mg (85%). This was methylated with Mel/MeOH in 97% yield and then deprotected in 99% yield to give tetrapeptide S (21). 

To a-hydroxysarcosine 68 (13.3 g, 52.6 mmol) and TEA (16.0 g, 158 mmol) in dry CH2C12 (100 mL) at —20 °C was added dropwise MsCl (6.63 g, 57.9 mmol). The mixture was warmed to rt after 2 h and stirred for 15 h. The solvent was removed and replaced with dry MeCN (50 mL). Powdered KI (8.73 g, 52.6 mmol) was added, followed by P(OMe)3 (7.83 g, 63.1 mmol). After vigorous stirring for 22 h, the solvent was removed and the residue was partitioned between EtOAc and H20. The aqueous layer was extracted with EtOAc and the combined organic layers were washed with brine, dried (MgS04), filtered, and concentrated. Chromatography (EtOAc/hexanes 9 1) gave the methyl ester of 69 as an oil yield 13.6g (75%). 

To 64 (70 mg, 58.9 pmol) in AcOH (2mL) was added Zn powder (0.5 g). This was stirred vigorously for 4h and filtered (Celite). The filter cake was rinsed (EtOAc) and the filtrate was concentrated. Chromatography of the residue (CH2Cl2/iPrOH/AcOH 10 1 0.1 to elute nonpolar material, then CH2C12/ iPrOH/AcOH 10 2 0.1) gave the deprotected material yield 52mg (84%). 

Diethyl(3-pyridyl)borane (3.38 g, 23 mmol) from Aldrich Chemical Co. Ltd. was added to a stirred solution of 3p-acetoxyandrosta-5,16-dien-17-yl trifluoromethanesulphonate (6.94 g, 15 mmol) in THF (75 ml) containing bis(triphenylphosphine)palladium(II) chloride (0.105 g, 0.15 mmol). An aqueous solution of sodium carbonate (2 M, 30 ml) was then added and the mixture heated, with stirring, by an oil bath at 80°C for 1 h, and allowed to cool. The mixture was partitioned between diethyl ether and water, the ether phase was dried (Na2C03), filtered through a short plug of silica, and concentrated. Chromatography, on elution with light petroleum-diethyl ether (2 1), afforded the 3 5-acetoxy-17-(3-pyridyl)androsta-5,16-diene (4.95 g, 84%) which crystallised from hexane, m.p. 144-145°C. 

To a solution of 3-trimethylsilylbromobenzene (7.62 g, 33.3 mmol) in diethyl ether (35 ml) was added 1.5 M n-butyl lithium in hexane (22.2 ml, 33.3 mmol) at 0°C over 10 min. Then the mixture was allowed to react 15 min at room temperature, cooled to -78°C and ethyl trifluoroacetate (14.2 g, 100 mmol) was added over 5 min. Then the mixture was allowed to react 15 min at -78°C, the cooling bath was removed and when the temperature rose to 0°C. 3 N HCI (35 ml) was added dropwise. The organic layer was separated, washed with water, brine, dried over MgS04 and concentrated. Chromatography (silica gel, cyclohexane/diethyl ether 90/10) followed by distillation under reduced pressure afforded the expected compound (zifrosilone) as a colorless oil (4.32 g, 53% yield), boiling point 120°C/0.8 mm Hg Rf 0.28 (cyclohexane/diethyl ether 95/5). 

Oxidation and Rearrangement A solution of 0.15 g (0.5 mmol) of the selenolactone in 20 mL THF is cooled to -20°C. 1 mL (5 Vo v/v) H202 is added and the mixture is stirred for 2 h. 1 mL of Et3N is then added and the temperature is allowed to reach 23 °C. After 10 min it is extracted with CHC13, washed with H20, dried over MgS04 and concentrated. Chromatography of the residue gives the product yield 46 mg (60%). 

---