Comparison of structure of gum exudate polysaccharides from the trunk and fruit of the peach tree (Prunus persica)

The peach tree (Prunus persica) produces gum exudates on its trunk and fruit. Tire former was extracted with water to give polysaccharide (PPN) and residual material was extracted with alkali giving structurally similar PPNA (NMR examination), which was formed in a slightly higher yield (42% compared with 37%). PPNA consisted of Ara, Xyl, Man, Gal, and uronic acids in a 36:7:2:42:13 molar ratio and was homogeneous on HSPEC with M-w 5.61(+/- 0.22) x 10(6) g mol(-1). Methylation analysis showed mainly nonreducing end (20%). and 3-O- (6%) and 4-O-substituted Arap and/or 5-O-substituted Araf units (14%) and nonreducing end-units of Xylp (13%). The core Galp units were mainly 3.6-di-O- (19%) and 3 4,6-tri-O-substituted (14%). The C-13 NMR spectrum of PPNA confirmed its complexity with 5 C-1 signals from delta 107.5-109.5 from alpha-L-Araf and a main one at delta 103.2 from the beta-D-Galp units. A controlled Smith degradation of PPNA gave 19% polymer (PPNAS), which was almost completely degraded, in a very low yield, to an inner core of PPNAS2 after a second cycle. This contained mainly beta-D-Galp units, that were nonreducing end- (25%), 3-O-(34%), and 2,3-di-O-substituted units (21%), with no evidence of 6-O-substitution. Partial hydrolysis of PPNAS with 0.1 M TFA at 100 degrees C removed Araf units, to give polymeric PPNAS60 (20% yield), which had Gal as its major component (85%). Methylation analysis showed a branched structure mainly nonreducing end- (18%), 3-O- (15%), 6-O- (45%). and 3,6-di-O-substituted Galp units (9%): its C-13 NMR spectrum had a C-1 main signal at delta 103.8 from beta-D-linked units. Under stronger hydrolysis conditions beta-D-GlcpA-(1 -> 6)-alpha beta-D-Gal and beta-D-GlcpA-(1 -> 2)-alpha beta-D-Mian were formed. The fruit gum polysaccharide (PPNF) was homogeneous with M-w 6.43(+/- 0.64) x 10(6) g mol(-1) and according to C-13 NMR and HMQC and TOCSY H-1 correlations, showing few structural differences. These were not apparent oil monosaccharide composition and methylation analyses. which only revealed quantitative variations. (C) 2007 Elsevier Ltd. All rights reserved.