Dicyclohexylcarbodiimide → N,N'-Dicyclohexylurea

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반응 단계

The procedure was adapted after Steroids, 1963, 2(6), 567-603 and is the same for (8) and (10) starting from (6) and (5), respectively. The TBDMS protected methyl ester of treprostinil (6) (46 mg, 0.09 mmoles) was dissolved in 2 ml dry pyridine and a pyridinium solution of the previously prepared pyridinium solution of 2-cyanoethylphosphate 1M (0.2 ml, 0.2 mmoles) (cf. Methods in Enzymology, 1971, 18(c), 54-57) were concentrated to dryness in vacuo at 40° C. Anhydrous pyridine was added and the reaction mixture was again concentrated; the operation was repeated twice in order to remove water completely. Finally the residue was dissolved in 2 ml anhydrous pyridine and 116 mg (0.56 mmoles) dicyclohexylcarbodiimide were added as a solution in 2 ml anhydrous pyridine. The reaction mixture in a closed flask was stirred magnetically for 48 hours at room temperature in the dark. 5 ml water were added and after one hour, the mixture was concentrated to a thick paste in vacuo. The reaction mixture was treated overnight at room temperature with 10 ml of a 1/9 water/methanol solution containing 100 mg sodium hydroxide. The white solid (dicyclohexylurea) formed was removed by filtration and it was washed well with water. The aqueous-methanolic solution was concentrated almost to dryness in vacuo, water was added and the solution was extracted with n-butanol (3×10 ml), then with methylene chloride (1×10 ml). The pH of the solution was adjusted to 9.0 by treatment with a sulfonic acid ion exchange resin (H+ cycle—Dowex); treatment with Dowex resin for a longer time (˜12 hours) lead to both the cleavage of the TBDMS group and the recovery of the free carboxyl group. The resin was filtered and the solution was concentrated to dryness affording the corresponding monophosphate 8 (33 mg, yield 68%).

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