Structure of Symbioimines

IR spectrum of symbioimine (35) showed absorption bands for hydroxyl (3450 cm-1), iminium (1690 cm-1), and sulfate (1240, 1140, 1050 cm-1) groups. The 13C NMR signal at 188.0 (C-5) implied the presence of an iminium functionality in this water-soluble amphoteric compound. Its structure, which consists of a characteristic 6,6,6-tricyclic iminium ring possessing an aryl sulfate moiety, was deduced by 2D-NMR analysis (Fig. 6).

The relative stereochemistry of 35 was deduced as follows. The large magnitudes of ha,2 = 12.0 Hz, ¡2,3 = 11.1 Hz, ¡3,4 = 11.1 Hz, ¡4,9 = 11-9 Hz, ]laM = 12.9 Hz, and J8a,9 = 12.9 Hz suggested that all seven of these protons, H-1a, H-2, H-3, H-4, H-7a, H-8a, and H-9a, were oriented in anti arrangements with respect to the tricyclic ring. Thus, three six-membered rings may show trans ring fusion with each other and that the methyl group (C-19) may be oriented in a pseudo-equatorial conformation with respect to the six-membered iminium ring with a twist-boat conformation. NOEs were observed for H-4/H-14 and H-4/H-18, suggesting that the aryl moiety may be oriented in a pseudo-axial conformation with respect to the cyclohexene ring with a twist-boat conformation. Finally, the stereostructure of 35 was confirmed by X-ray crystallographic analysis. The absolute stereochemistry of 35 was confirmed to be 2R, 3R, 4S, 9R, 12S, based on the value of the Flack parameter 0.03(13).

Neosymbioimine (36) was found to be a congener of 35 possessing a 6,6,6-tricyclic iminium ring, an aryl sulfate moiety, and three methyl groups.

>-'~\ long-range couplings Fig. 6 Planar and stereo structure of symbioimine (35) based on 2D-NMR analysis

0 0

Post a comment