*2.2.7 Miscellaneous alkaloids*

*Current Topics in Chirality - From Chemistry to Biology*

C13-C23 double bond (**Figure 8**) [30].

for the psychoactive effects [33].

*2.2.6 Indole alkaloids*

The most important pyrrolizidine alkaloids senecionine, seneciphylline, retrorsine and senkirkine, contain the 4-azabicyclo [3.3.0] octane system with senecionine and seneciphylline differing only for the presence in the latter of the

Indole alkaloids constitute a wide class of natural products most of them pharmacologically important and characterized by very different activities [31]. In the recent years, attention has been focused on the biological activity of yohimbine which is a monoterpenoid indole alkaloid (**Figure 9**). It displayed the treatment of erectile functional disturbance and anxiogenic [32]. Hydroindole alkaloids such as mesembrine and congeners (mesembrenone, Δ7 mesembrenone, mesembranol and its stereoisomer epimesembranol) have been isolated from Sceletium species used

The vinca alkaloids were isolated from the Madagascar periwinkle, Catharantus roseus G. Don., which included a class of about 130 terpenoid indole alkaloids [32]. In early 1965, people obviously know their clinical quality. And this group of compounds has been taken advantage of as an anticancer servant for more than 40 years and is a symbol of the compound that gives the trend to drug development [34, 35]. Among these base (+)-vincamine exhibits a valuable therapeutic activity in cerebral insufficiencies. Due to the presence of three stereogenic centers eight stereoisomers

(four enantiomeric pairs) are in fact possible (**Figure 10**) [36].

*Molecular structures of four toxic PAs. (1) senkirkine; (2) senecionine; (3) retrorsine; (4) seneciphylline.*

*Molecular structures of: (1) morphine; (2) codeine; (3) oripavine; (4) thebaine; (5) pseudomorphine.*

**44**

**Figure 9.**

*Molecular structure of yohimbine and mesembrine.*

**Figure 8.**

**Figure 7.**

Steroidal alkaloids including verticine and verticinone are distinguished by cholestane carbon skeleton (isosteroid alkaloids) with a hexacyclic benzo [7, 8] fluoreno [2,1-b] quinolizine nucleus (**Figure 11**). These compounds have been isolated from plants from Liliaceae family typically Bulbus fritillariae used as a traditional medicine in Japanese, Turkish, Pakistani, and south-east Asian folk medicines [10]. Pharmacological studies demonstrate that verticine and verticinone in Bulbus Fritillariaeare the primary active ingredients responsible for the antitussive activity [37].

Stemona, belonging to Stemonaceae family, is known in the folk medicine of Southeast Asia, China, and Japan since its Phyto-preparations (primary the roots) are used to treat diseases about bronchitis, pertussis and tuberculosis. Interestingly many alkaloids, structurally defined as pyrido[1,2-α]azepines, have been recognized in this plant species and are considered the important pharmacological activity. All the Stemona alkaloids are polycyclic and contain multiple stereocenters [38]. Up to now, there are about 139 Stemona alkaloids which the scientist isolated (**Figure 12**).

**Figure 10.**

*Molecular structure of major vinca alkaloids isolated from* Catharanthus roseus*: (+)-Catharanthine (A) and (*−*)-Vindoline (B).*

#### **Figure 11.**

*Molecular structures of verticine and verticinone.*

**Figure 12.** *Molecular structure of stemonamine and parvistemoline.*
