SYNTHESIS AND CONFORMATIONAL-ANALYSIS OF PLANT HORMONE (AUXIN) RELATED COMPOUND 2-(INDOL-3-YL) ETHYL BETA-D-GALACTOPYRANOSIDE AND ITS 2,3,4,6-TETRA-O-ACETYL DERIVATIVE

The synthesis, structure analysis by X-ray diffraction and NMR spectro scopy (including H-1{H-1}NOEs) of 2-(indol-3-yl)ethyl 2,3,4,6-tetra-O- acetyl-beta-D-galactopyranoside (4) are described. The per-O-acetylate d derivative of 2-(indol-3-yl)ethyl beta-D-galactopyranoside (4) was prepared along with the isomeric alpha-D-galactopyranose 1,2-orthoacet ates (3 exo- and endo-stereomers) by condensation of 2,3,4,6-tetra-O-a cetyl-alpha-D-galactopyranosyl bromide (1) with the aglycone alcohol ( 2). The analogous condensation of 1 and 2-phenylethanol yielded a mixt ure of 2-phenylethyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside ( 6) and isomeric alpha-D-galactopyranose 1,2-orthoacetates (5). Compoun d 4 crystallized in the monoclinic system, space group C2, a = 22.385( 2), b = 7.865(2), c = 28.761(3) Angstrom, beta = 102.1(1)degrees, Z = 8, with two symmetrically independent molecules in the asymmetric unit . In both molecules beta-D-galactopyranose rings are in the C-4(1) cha ir conformation. The conformational analysis of 4 and the analogous un protected conjugate (4), based on molecular mechanics calculations an d molecular dynamics simulations, is presented. The conformational sta bility about the bond of conjugation and relative orientation of the i ndole ring towards the beta-D-galactopyranose moiety are discussed.