Secologanin aglucone

The full paper of Tietze s biogenetic-type synthesis of secologanin aglucone methyl ether and sweroside aglucone methyl ether has been published (Vol. 5, p. 18), and a second paper independently reports in full the rapid enzymic cleavage of secologanin to the bicyclic hemiacetal previously described by R. T. Brown (Vol. 7, p. 27) longer reaction times result in the formation of (146). ... 

Scheme 5.17. Synthesis of secologanin aglucon ethyl ether 99.

In the tryptamine series, acidic deglucosylation of (3i -74c) (Fig. (22)) gave the pentacyclic compound (3i -95a) (see in Fig (18), according to the most stable secologanin aglucone type and cyclized between C-21 and N-1 without fragmentation. 

Evidently, in most cases the transformations are under thermodynamic control. The structure of secologanin subunit of all isolated aglucones corresponded to the energetically more favoured structures in agreement with the results obtained on the bakankosine derivatives. It means that the favoured direction of the oxacyclization is 0-17- C-21 in the dihydro derivatives (according to type 1H of Fig. (7)), and 0-17- C-19 in the natural ones (according to type 12 of Fig. (7)). The result of azacyclization depended on the atom N-l and N-4. When both N atoms were protected (3i -92a) and (3i -92b), the process stopped at the tetracyclic level (3i -96a) and (3i -96b). When both of them were unprotected (in (3i -90a) and (37 -90b)), the azacyclization preceded the... 

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