Enzymatic Strategy for the Resolution of New 1-Hydroxymethyl Tetrahydro- β-carboline Derivatives in Batch and Continuous-Flow Systems.

Many alkaloids containing a tetrahydro- β-carboline skeleton have well-known therapeutic effects, leading to increased interest in the synthesis of these natural products. Enantiomers of N-Boc-protected 1-hydroxymethyl-1,2,3,4-tetrahydro- β-carboline [(±)- 7], 1-hydroxymethyl-6-methoxy-1,2,3,4-tetrahydro- β-carboline [(±)- 8], and 1-hydroxymethyl-6-fluoro-1,2,3,4-tetrahydro- β-carboline [(±)- 9] were prepared through enzymecatalyzed asymmetric acylation of their primary hydroxyl group. The preliminary experiments were performed in a continuous-flow system, while the preparative-scale resolutions were done as batch reactions. Excellent enantioselectivities ( E>200) were obtained with Candida antarctica lipase B (CAL-B) and acetic anhydride in toluene at 60 °C. The recovered alcohols and the produced esters were obtained with high enantiomeric excess values ( ee≥96 %). The O-acylated enantiomers [( S)- 10-( S)- 12)] were transformed into the corresponding amino alcohols [( S)- 7-( S)- 9)] with methanolysis. Microwave-assisted Boc removals were also performed and resulted in the corresponding compounds ( R)- 4-( R)- 6 and ( S)- 4-( S)- 6 without a drop in the enantiomeric excess values ( ee≥96 %). [ABSTRACT FROM AUTHOR]