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It is possible that the vinylogs of -amino acids of the formula I, according to the principle of vinylogy (1), could prove to be interesting compounds, inter alia, as substrates for certain enzymes.

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A p~l~s a c c h a r i d e , precipitated by cetyltrimethylamnloniun~ hydroxide from the nondialyzable portion of birch xylem sap, contained D-galactose, D-mannose, and D-glucose in a molar ratio of 2:1.4:1 and small amounts of D-glucuronic acid. Periodate oxidation studies indicated that the polysaccharide was branched and contained a high proportion of periodateresistant monosaccharides. This was confirmed by methylation and hydrolysis which yielded 2,3,4,6-tetra-0-methyl-D-glucose (2.0 moles); 2,4,6-tri-0-methyl-D-~nannose (0.9 mole); 2,4,6-tri-0-methyl-D-galactose (3.8 moles); unidentified tri-0-methyl hexose (1.2 moles); and 3,5-di-0-methyl-D-mannose (1.8 moles). T h e latter, a new di-0-methyl-D-mannose, showed the presence of D-mannofuranose units in the polysaccharide. This, together with the 1 -+ 3 linked a-D-mannopyranose units, maltes this polysaccharide unique among plant products. Immunochemical tests with antipneumococcal and antiparatyphoid B horse sera confirmed the presence of D-glucuronic acid and D-glucopyranose non-reducing end groups and supported the other structural conclusions by showing that there were few, if any, 1 -+ 4 and 1 -+ 6 linked D-mannopyranose units or D -g a l a~t~p y r a n~s e non-reducing end groups.Until recently very little was known about the chemistry of wood saps, apart froin the sucrose content of maple sap and the glucose and fructose contents of birch sap (1). Interest in the other constituents of these saps arose because it seemed possible that wood sap might contain intermediates or precursors in the synthesis of wood polysaccharides. Previous papers from this laboratory have described the isolation and structural investigation of a polysaccharide from maple sap (2, 3), analyses of the oligosaccharides present in birch (1) and maple (4) saps, and a study of the glycoside hydrolase activity in the xylem saps of birch and maple (5).The present paper reports the isolation and structural investigation of a polysaccharide from the xylem sap of white birch (Betula papyrifera Marsh).The polysaccharides, isolated from the non-dialyzable sap constituents by precipitation with ethanol, showed several peaks on rnoving-boundary electrophoresis (6) and yielded galactose, glucose, mannose, xylose, arabinose, rhamnose, and a uronic acid on acid hydrolysis. A polysaccharide that was homogeneous by electrophoresis and ultracentrifugation was obtained from this mixture by precipitation with cetyltrirnethylammonium hydroxide (7). This polysaccharide, which made up 27% of the non-dialyzable material, contained D-galactose, D-mannose, and D -~~u c o S~ in a molar ratio of 2:1.4: 1 and 20y0 of hexuroilic acid as estimated by the carbazole method ( 8 ) . The small alnount of hexuronic acid obtained by hydrolysis of the polysaccharide was converted to its parent monosaccharide by successive reduction and hydrolysis of its methyl ester, methyl glycoside. The chromatographic identification of glucose from this procedure indicated that the hexuronic acid was D-glucuronic acid, and t...