Synthesis and confromational analysis of the plant hormone (auxin) related 2-(indol-3-yl)ethyl and 2-phenylethyl β-D-xylopyranosides and their 2,3,4-tri-O-acetyl derivatives

Article abstract of DOI:10.1016/0008-6215(95)00037-T

The synthesis, structure analysis by X-ray diffraction and NMR spectroscopy (including also 1H <1H>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 β-D-xylopyranoside (4β) and 2-phenylethyl β-D-xylopyranoside (7β) were prepared by Koenigs-Knorr condensation of the aglycone alcohols with 2,3,4-tri-O-acetyl-α-D-xylopyranosyl bromide.Glycoside 4β was deprotected to yield 2-(indol-3-yl) ethyl β-D-xylopyranoside (6).The crystal structures of 4β and 7β were determined.The crystals of both compounds are monoclinic, space group P 2₁ with a=11.985(1), b=7.317(1), c=12.428(1) Angstroem, β=93.2(1) deg, Z=2 (4β); a=5.809(1), b=19.833(1), c=8.912(1) Angstroem, β=106.0(1) deg, Z=2 (7β).The β-D-xylopyranose rings are in the 4C₁ chair conformation.The results of the theoretical conformational analysis are compared with the values obtained from the experimental measurements in solid state and solution. Keywords: Auxin; Xylopyranosides; X-ray diffraction; NMR spectroscopy; NOE; Molecular dynamics