SYNTHESIS AND CONFORMATIONAL-ANALYSIS OF 2-(INDOL-3-YL)ETHYL ALPHA-L-ARABINOPYRANOSIDE AND ITS 2,3,4-TRI-O-ACETYL DERIVATIVE

2-(Indol-3-yl)ethyl alpha-L-arabinopyranoside (5) was prepared by Koni gs-Knorr condensation of the aglycon alcohol with 2,3,4-O-acetyl-beta- L-arabinopyranosyl bromide, followed by O-deacetylation. The structure of the per-O-acetylated derivative (3) was determined. The crystals o f 3 are trigonal, space group P3(1)21 with a = 8.367(4) Angstrom, c = 53.34(2) Angstrom, and Z = 6. The conformational analysis is based on the results obtained from X-ray structure analysis (3), H-1{H-1}NOE me asurements (3), and such computational chemistry methods as molecular mechanics and molecular dynamics simulations (5). The alpha-L-arabinop yranose ring is in a C-4(1) chair. Theoretical conformational analysis has been focused on the most flexible part of the molecule defined by four torsion angles about bonds which connect the carbohydrate residu e and the indole nucleus. The conformer observed in the solid state is one of several possible forms indicated by molecular mechanics and mo lecular dynamics. The most probable forms are identified. In all obser ved conformers, the molecule studied maintains the indole ring approxi mately perpendicular to the side chain, which may be one of the prereq uisites for bioactivity.