名称:
An Efficient Process for Synthesis of 3-(R)-3-(2,3-Dihydrobenzofuran-5-yl)- 1,2,3,4-tetrahydropyrrolo[3,4-b]quinolin-9-one
摘要:
3-(R)-3-(2,3-Dihydrobenzofuran-5-yl)-1,2,3,4-tetrahydropyrrolo[3,4-b]quinolin-9-one (1) is a key intermediate in the synthesis of pyrroloquinolone analogues, a series of highly potent and selective phosphodiesterase 5 (PDE5) inhibitors. Racemic 1-(2,3-dihydrobenzofuran-5-yl)-2,3,4,9-tetrahydro-1H-beta-carboline (6, Scheme 2) was prepared by Pictet-Spenger condensation in 84% isolated yield with > 97% chemical purity. The desired intermediate, 1-(R)-1-(2,3-dihydrobenzofuran-5-yl)2,3,4,9-tetrahydro-1H-beta-carboline N-acetyl-D-leucine salt (8), was obtained in 35% isolated yield with high chiral purity (> 97% ee) from the chemical resolution of 6 with N-acetyl-D-leucine (7). A racemization step was developed for recycling enriched 1-(S)-beta-carboline 9 freebase (8/9, 25 +/- 3%/75 +/- 3%) to a near racemic mixture (8/9, 47 +/- 1%153 +/- 1%). Furthermore, the resolving reagent 7 was recovered in > 76% yield, which, together with the recycled racemic mixture (8/9, 47 1%153 1%), afforded 35% more salt 8 after two recycles (>= 97.0% ee). The salt 8 was converted to 1-(R)-1-(2,3-dihydrobenzofuran-5-yl)-2-benzyl-2,3,4,9-tetrahydro-1H-beta-carbo- line (10) in excellent yield (94%). A modified Winterfeldt oxidation of compound 10 using Aliquat 175 as a phase transfer catalyst produced 3-(R)-2-benzyl-3-(2,3-dihydrobenzofuran-5yl)-1,2,3,4-tetrahydropyrrolo[3,4-b]quinolin-9-one (12) in moderate 42% yield. Hydrogenolysis of compound 12 gave the desired compound 1 in quantitative yield with retention of chiral purity (>= 97.0% ee). This efficient, reproducible, economical, and nonchromatography scale-up process could be used to make multikilogram quantities of compound 1.