INTRODUCITON
Melicoccu bijuga (Sapindaceae) a native plant of tropical America, is highly disseminated in Venezuela. It exudes a clear gum which is very soluble in water. Earlier studies on Acacia senegal' and Acacia xunthophloeuz gum exudates established the importance of carbon-13 NMR, in combination with chemical methods, in the structural study of these complex polymers. The spectra of M. bzjugu gum and its degradation products reported here were anaIyzed in relation to relevant model compounds. EXPERIMENTAL Origin and putification of gum sample. -Gum from Melicocca bijuga ("man&r") was collected in Maraca&o, Venezuela, South America in 1986. The gum (92 g) dissolved readily in cold water (3.1 L). The very clear solution was passed through Whatman No. 1 and 42 filter papers and dialyzed against running tap-water for two days; the gum was recovered by freeze-drying. Geraeral experimental methods -Standard methods of gum analysis were used3-5. The solvent systems used in paper chromatography were (a) 3 : 18 : 1: 4 AcOH-EtOAc-HCO,H-H,O; (6) 1: 5 : 3 : 3 (upper layer) benzene-l-butanol-pyridine-H,O; (c> 10:5: 1 EtOH-0.033 M H,PO,-1-butanol; and (d) 4: 1:5 (upper layer) 1-butanol-EtOH-H,O.
Before using solvent (cl, papers were dipped in 0.3 M NaH,PO, solution and air-dried. Optical rotations at equilibrium were measured at room temperature in an Atago-Polax D polarimeter, using solutions (0.7-1.0%)