SYNTHESIS AND CONFORMATIONAL-ANALYSIS OF THE PLANT HORMONE (AUXIN) RELATED 2-(INDOL-3-YL)ETHYL AND 2-PHENYLETHYL BETA-D-XYLOPYRANOSIDES AND THEIR 2,3,4-TRI-O-ACETYL DERIVATIVES

The synthesis, structure analysis by X-ray diffraction and NMR spectroscopy (including also H-1 {H-1}NOE measurements), as well as molecular mechanics and dynamics of D-xylopyranose conjugates of 2-(indol-3-yl)ethanol (1) and 2-phenylethanol (2) are described. The per-O-acetylated derivatives of 2-(indol-3-yl)ethyl beta-D-xylopyranoside (4 beta) and 2-phenylethyl beta-D-xylopyranoside (7 beta) were prepared [along with corresponding alpha-D-isomers (4 alpha and 7 alpha) and 1,2-O-orthoacetates (5,8)] by Koenigs-Knorr condensation of the aglycone alcohols with 2,3,4-tri-O-acetyl-alpha-D-xylopyranosyl bromide. Glycoside 4 beta was deprotected to yield 2-(indol-3-yl) ethyl beta-D-xylopyranoside (6). The crystal structures of 4 beta and 7 beta were determined. The crystals of both compounds are monoclinic, space group P 2(1) with a = 11.985(1), b = 7.317(1), c = 12.428(1) Angstrom, beta = 93.2(1)degrees, Z = 2 (4 beta); a = 5.809(1), b = 19.833(1), c = 8.912(1) Angstrom, beta = 106.0(1)degrees, Z = 2 (7 beta). The beta-D-xylopyranose rings are in the C-4(1) chair conformation. The results of the theoretical conformational analysis are compared with the values obtained from the experimental measurements in solid state and solution.