pears downfield at 6 7. 77 (cf., 7.82 in IIb) and one of the methoxy groups appears upfield a t 6 3.68 (cf., 3.60 in IIb), a methoxy can be placed at C-1 and a hydrogen a t C-11 (5, 10, 11)6. The UV spectrum [A,,, ( C H 3 O H ) nm (log 6): 217 (4.65), 280 (4.08),307 (4.16), and 313 sh (4.16)] is characteristic of a 1,2,3,9,10-pentaoxygenated aporphine (12, 13) and distinctly different from a 1,2,8,9,10-pentaoxygenated aporphine (10). Thus, the only substitution pattern for Alkaloid B that is consistent with both the UV and NMR spectra (singlets for the two aromatic hydrogens) is a C-172,3,9,10-pentaoxygenated aporphine with a C-1 methoxy group.
The methylenedioxy group could be located a t C-2,3 or C-9,lO. The location of the methylenedioxy group at C-9,lO and the methoxy groups at C-2 and C-3 is preferred since a 2H singlet a t 6 5.87 is observed for the methylenedioxy protons in Alkaloid B (cf., 5.85 in IIb). The protons of a methylenedioxy group located at C-2,3 form an AB quartet ( ) just as they do when located at C-1,2 (5). Additional evidence for this oxygenation pattern comes from observing the chemical shifts of the methoxy resonances. When methoxy groups are located at C-9 and C-10, they usually appear as overlapping signals near 6 3.9 (5, 11); but when methoxy groups are located at C-1, 2, and 3, they appear as discrete signals ( ) as observed in the NMR spectrum of Alkaloid B.
Based on this evidence, we propose that Alkaloid B be represented as (+) -3-methoxy-N-acetylnornantenine (IIe). The absolute stereochemistry at C-6a follows by noting the large positive Cotton effect in the circular dichroism spectrum4 at 243 nm ([el = +199,000; 1.80 mg/50 ml), which has been correlated with the S-configuration at C-6a (6). To our knowledge, these alkaloids (IIb and IIe) represent the first two examples of naturally occurring N-acetylaporphine alkaloids.