Mannose intramolecular hydrogen bonding

P2i Z = 2 Dx = 1.384 R = 0.071 for 3,427 intensities. Absolute configuration confirms that nogalose is a derivative of 6-deoxy-L-mannose. The molecule has an open-chain shape, with a sickle carbon-chain conformation, thereby permitting formation of an intramolecular hydrogen-bond between O-l-H and 0-5-H at either end of the chain. 

The position of jS-mannose in this order deviates from what could be expected on the basis of the inffamolecular hydrogen-bonding patterns shown in Figure 4. This deviation could be due to alternative arrangements of the intramolecular hydrogen bonds, (see also P. R. Muddasani, E. Bozo, B. Bemet and A. VaseUa, Helv. Chim. Acta, 1994, 77, 257-290). 

Additional evidence was obtained for the structure (110) of the compound derived from D-mannose, ammonia, and ethyl acetoacetate. This substance, when suspended in water and kept at room temperature, is slowly hydrolyzed, giving di-n-mannosylamine, isolated in the crystalline state, and n-mannose, characterized as its phenylhydrazone. Acetylation gives a tetra-O-acetyl derivative (111). The infrared spectrum of this acetate shows bands at 3280 cm. , attributable to the presence of an intramolecularly bonded NH group, and at 1658 cm. S probably due to the carbonyl group of the /3-amino a, 8-unsaturated ester also involved in a hydrogen bond. Mild, acid hydrolysis of (111) gives 2,3,4,6-tetra-O-acetyl-D-mannose. 

---