Anhydromacrosalhine-methine

Yu, P., Wang, T., Li, J., Cook, J. M. Enantiospecific Total Synthesis of the Sarpagine Related Indole Alkaloids Talpinine and Talcarpine as Well as the Improved Total Synthesis of Alstonerine and Anhydromacrosalhine-methine via the Asymmetric Pictet-Spengler Reaction. J. Org. Chem. 2000, 65, 3173-3191. 

The structure XLIX for macrosalhine and L for anhydromacrosalhine methine are strongly. supported by their behavior on electron impact. When introduced into the mass spectrometer macrosalhine chloride undergoes thermal Hofmann degradation and the mass spectrum ob.scrved is that of the methine base LII, C21H26N2O2, M 338, which is an isomer of macroline (XVIII). As expected, several of the peaks in the... 

A 2,7-dihydropleiocarpamine unit is also present in the alkaloid macrocarp-amine (237), an amorphous base recently isolated from the bark of Alstonia macrophylla Wall. The second component is anhydromacrosalhine methine, which is attached to pleiocarpamine by a single bond between C-2 of the latter... 

Subsequently, Cook disclosed a similar partial synthesis of macrocarpamine (323) by coupling (—)-anhydromacrosalhine-methine (344) with natural pleiocarpamine (342) in anhydrous 0.2 N HCl in THE (Scheme 24) (228-230), providing support for the earlier biogenetic proposal of Hesse (231). The required (—)-anhydromacrosalhine-methine was first partially synthesized from (-l-)-ajmaline (345) to provide an authentic sample (Scheme 25). Degradation to the hemiacetal 346 was carried out following the improved procedure of Sakai (232). This was followed in succession by dehydration, regioselective oxyselenation, selenoxide elimination, and finally 1,4-elimination to yield anhydromacrosalhine-methine (344) in 85% yield. 

The enantiospecific synthesis of anhydromacrosalhine-methine (344) commenced with the tetracyclic ketone 343 which was converted into alstonerine (347) as described previously (227). Reduction of alstonerine, followed by dehydration of the resultant allylic alcohol, provided (—)-anhydromacrosalhine-methine (344), identical with material prepared from natural (+ )-ajmaline (Scheme 25) 228,230). In the context of a synthesis of talpinine and talcarpine, an improved synthesis of (—)-anhydromacrosalhine-methine was also achieved from improved routes to the tetracyclic ketones 348 and the enol ether 349, key intermediates in the talpinine/talcarpine synthesis (233). 

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