Heteroyohimbane

The natural representative of this group is 8-yohimbine or ajmalicine first, found in Yohimbe and in Rauwolfia serpentina Benth. ex Kurz (Volume VII). 

Since 1957 five new alkaloids belonging to this group have been described rauvanine, raunitidine, rauniticine, neoreserpiline, and holoinine. Other sources, as given, have also been found for ajmalicine, Rauwolfia sumatrana (Miq.) Jack. (33) and R. javanica Koord et Val (34) tetrahydroalstonine, Lochnera lancea Boj. (ex A.DC.) (35) and 

Alstonia constricta F. Muell. (36) alstonine, R. vomitoria (37) aricine, Aspidosperma marcgravianum Woodson (37) reserpiline, R. decurva Hook. (38) isoreserpiline, R. cambodiana Pierre (39), R. decurva, and Ochrosia poweri F. M. Bailey serpentinine, R. vomitoria (37) and R. javanica (34). 

Of the five new alkaloids, the first four are tertiary bases. Holoeinine is a quaternary base from R. samdwicensis A.DC. identified as the Nb methyl quaternary derivative of isoreserpiline (40), 

Neoreserpiline, C23H28O5N2, mp 120°-131°, [a]D-78° (EtOH), from R. perakensis, is a dimethoxyheteroyohimbane of unknown structure (41). 

---

The stereochemistry of the heteroyohimbanes has largely been elucidated, and a total synthesis of ajmalicine has been achieved. 

Aside from the fact that some of the heteroyohimbanes (LXXVII) carry substituents at positions 10 and/or 11, they differ in their configuration at the four centers of assymetry, 3, 15, 30, and 19, to which may be added the possibility of conformational isomerism. Table II summarizes the eight possible types of isomerism, their relations to the corresponding yohimbanes, and the alkaloids known in each type. The solutions of the various stereochemical problems were arrived at by a combination of methods, which follow. 

Rauvanine, C23H28O5N2.5H2O, mp 129°-135°, [a]D + 32 (CHCI3) has been isolated from JR. vomitoria (65). It contains three methoxyls and its UV-, IR-, and NMR-spectra indicate clearly that it is a 5,6-dimethoxy heteroyohimbane. Stereochemical criteria relegate it to ajmalicine and consequently its structure is XCIIb, indicating a very close relation to raumatorine which accompanies it in the plant (65,48). 

Alstonia alkaloids. A group of over 250 differing monomeric and dimeric monoterpenoid indole alkaloids from the genus Alstonia (Apocynaceae) having aspidospermidine, corynanthean, heteroyohimbane, and related indole skeletons. The A. a. are isolated from leaves, roots, and bark of wild Alstonia species (bushes, often fairly large evergreen trees) with the exception of A. scholaris which can be cultivated. 

In a synthesis of heteroyohimbane alkaloids tetrahydroalstonine 362 and akuammigine 363, Uskokovic prepared a chemoenzymatic process alcohol 364 [85, 86]. This compound afforded ester 366 with R configuration at C-15 after orthoester rearrangement through a chair-Hke transition state 365. Functionahza-tion at C-16 followed by a stereoselective hydroboration-oxidation afforded compound 367 with the DE rings framework of the alkaloids (Scheme 6.61). The same rearrangement has been used by Bosch in a synthesis of alkaloid tubifoHne 368 [87] (Scheme 6.61). 

Indole Alkaloids Yohimbane, heteroyohimbane and oxindole groups. 

Heptoses, C3 Herqueinone, Y12 Hesperetin, Y6 Hetacillin, Y29 Heteratisine, K33 Heterohelicenes, X6 Heteroyohimbane alkaloids, K7 Hexahelicene, X6 Hexahydrochamaecynone, T20 Hexahydrocoriolin, T9 Hexahydrophenylalanine, A5 Hexahydrotyrosine, A5 Hexitols, Cl Hexoestrol, A45 Hexoses, Cl Hibaene, T35 Hibiscus acid, A30 Himachalenes, T12, T8 ... 

---