Zephyranthine reacts with periodate faster than dihydrolycorine (XI), and gives an isopropylidene derivative, C
19H
23O
4N, m.p. 156-157° (decomp.). Therefore, it seems that the two hydroxyl groups in this alkaloid are vicinal and
cis each other. Diacetylzephyranthine was oxidized with permanganate to give a lactam diacetate C
20H
21O
7N, m.p. 252-253° (decomp.), whose infrared spectrum in chloroform showed a peak at 1639cm
-1, characteristics of a six-membered lactam ring. The lactam, C
16H
17O
5N, m.p. 268-270° (decomp.) which was obtained by alkaline hydrolysis of the lactam diacetate, gave a dialdehyde on periodate oxidation. The dialdehyde, C
16H
13O
5N, m.p. 210-211° (decomp.); [α]
D23 +83.52° (c=0.54, CHCl
3), was shown to be identical by the mixed melting point and infrared spectral comparison with the authentic dialdehyde (VIII) prepared from lycorine. Since this dialdehyde has the same direction and value in the optical rotation as those of the dialdehyde from lycorine whose absolute configuration had been established, the hydrogen at 3a-position should be in an α-configuration.
These results indicate that zephyranthine (III) is an alkaloid with a lycorane skeleton, and its two hydroxyl groups are situated at C-1 and C-2.
A treatment of zephyranthine monotosylate (XVIII), C
23H
25O
6NS, m.p. 178-179° (decomp.) with lithium alminum hydride gave monodeoxy derivative (XIX), m.p. 169-170°, [α]
D25 -100.00° (c=0.96, CHCl
3), which was characterized as its hydrochloride, C
16H
19O
3N⋅HCl, m.p. 264-265° (decomp.). This monodeoxy derivative was identical with the known α-dihydrocaranine. Based on this finding and the fact that the two hydroxyl groups in zephyranthine are
cis, zephyranthine can be formulated as XVII which has been proved to be identical with α-dihydro-2-epilycorine (XXIV), derived from lycorine.
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