Terrestrial Alkaloids

Steroid alkaloids have been isolated from four famihes of terrestrial plant sources (Soianaceae l iliaceae pOijnaceae and Buxaceae) two animal sources (Saiamandra and Phjllobates) and several marine sources. Steroid alkaloids can be classified based on stmcture and fall into a variety of categories. The spirosolanes contain a cholestane skeleton with a C20 spiroaminoketal moiety, as exemplified by the most abundant members of this class, veramine... 

Tian-Shung W, Li-Shian S, Shang-Chu K. Alkaloids and other constituents from Tribulus terrestris. Phytochemistry 1999 50 1411-1415. 

Bremner J, Waya S, Southwell I, et al. A revised structure for the alkaloid, tribuluste-rine, from Tribulus terrestris L. Aust J Chem 2004 57 273-276. 

In an effort to identify possible sources of the 16 alkaloids found in the skin of the Panamanian poison frog Dendrobates auratus, ants from a total of 61 terrestrial nests were analyzed [124]. The alate queens of one species of myr-micine ants (Solenopsis (Diplorhoptrum) sp.) collected at Cerro Ancon were found to contain the decahydroquinoline (-)-ds-195A (112) which was also present as a minor alkaloid in the skin of the microsympatric population of D. auratus. Moreover, from wingless ants of two nests collected at Isla Taboga and identified as Megalomyrmex silvestrU the same workers isolated the stereo-isomeric 3,5-disubstituted pyrrolizidines rfs-251 K (117) and trans-251 K (118) in the same ratio 3 1 that was present in the skin of a microsympatric population of D. auratus (Fig. 20) [124]. 

The dimeric carbazole alkaloids often occur along with the corresponding monomeric carbazoles in terrestrial plants [7,62] (Scheme 7). Clausenamine-A was obtained by Wu from the stem bark of Clausena excavata [63]. Clausen-amine-A and its synthetic analogs, like bis(O-demethylmurrayafoline-A), show cytotoxic activities against diverse human cancer cell lines [64] and exhibit moderate antimalarial activity [65,66]. Furukawa isolated l,r-bis(2-hy-droxy-3-methylcarbazole) and bismurrayaquinone-A, the first dimeric car-bazolequinone alkaloid found in nature, from Murraya koenigii [67]. 

Roitman, J.N. and Banter, K.E. 1995. Livestock poisoning caused by plant alkaloids, in Blum, M.S., Ed., The toxic action of marine and terrestrial alkaloids. Alaken Inc., Fort Collins, pp. 53-124. 

As for the indole alkaloids harmaline and harmine (Fig. 4), their biosynthesis was stimulated in emhryogenic callus of T. terrestris at concentrations of 66.4 0.5 and 82.7 0.6 /rg/g dw, respectively." Harmaline stimulates the central nervous system while harmine is cytotoxic to human leukemia cell lines HL-60 and K562. 

Since the late 1960s, several carbazole alkaloids oxygenated in the 3-position were isolated from diverse natural sources, the majority of which were isolated from different plant sources. However, in 1979, Moore et al. reported the isolation of two unusual, non-basic, 3-oxygenated carbazole alkaloids, hyellazole (245) and chloro-hyellazole (246), from the blue-green marine algae Hyella caespitosa (225). These alkaloids have structures entirely different from those of the carbazole alkaloids isolated from terrestrial plants. 

The teleocidins from terrestrial actinomycetales and the lyngbyatoxins from marine cyanobacteria (Chart 8.3.P) are peptide alkaloids well known for their tumor promoting ability. 

Metabolic transformations are characterized by high speed and yield, as well as high regio-, diastereo-and enantio-specificity. Errors in the stereochemistry of the molecules that serve to construct the genetic material are smaller than for the planetary motions. With secondary metabolites, however, enantiomerically inq)ure con unds are also encoimtered, typkally with monoterpenes and alkaloids from terrestrial plants even ant dal pathways in the same organism have been found, albeit as rare events (Guella 1998). 

Although very few terrestrial plant alkaloids contain halogen, brominated alkaloids have been reported from the marine environment. From the Okinawan marine sponge Hymemacidon sp., several bromopyrrole alkaloids have been described, e.g., tauroacidins A and B, Fig. (35) [262], konbuacidin A, Fig. (36) [263] and spongiacidins A-D [264]. Several species of sponges contain hymenialdisine, Fig. (37), which has been shown as a potent inhibitor of nuclear factor kappa B and interleukin-8 production in vitro [265,266]. 

Three new chlorinated welwitindolinone alkaloids, e.g. 218, have been isolated from the terrestrial cyanophytes Fischerella muscicola and Fischerella major [169]. 

The biosynthesis of organohalogens has seen enormous interest since the first survey, and several examples are mentioned earlier in the present review. Space does not allow for full coverage of this topic, but some additional examples are presented here. The reader is also directed to general reviews on the biosynthesis of marine natural products, many of which contain halogen (2398-2401), terrestrial fungal (basidiomycetes) metabolites (2402), and halogenated alkaloids (2403). 

Huber U, Moore RE, Patterson GML (1998) Isolation of a Nitrile-Containing Indole Alkaloid from the Terrestrial Blue-Green Alga Hapalosiphon delicatulus. J Nat Prod 61 ... 

Not surprisingly, although the evolution of sequestered microbial toxins appears to be rather widespread in marine environments, sequestration of defensive alkaloids in the apparent absence of microorganisms may generally characterize the chemical defenses of terrestrial animals. Careful searches for possible microbial syntheses of defensive compounds (allomones) have not been generally implemented, but recent studies in a few laboratories raise the possibility that microbial endosymbionts may be of major importance in the biogenesis of selected insect deterrents. 

Because of the enormous biomass of mites such as oribatids, their peculiar natural products might be more abundant in unrelated animals of terrestrial ecosystems.126 So, the chemistry of skin alkaloids in poisonous frogs often reflects their recent arthropod diet such as oribatids and ants.126 Moreover, several ants might be specialized on certain oribatid mites,127 whereas certain mites often prefer food such as pigmented fungal hyphae.126 Since alkaloids in scheloribatid mites are not present in larvae but found only in adults,121 the compounds might be either biosynthesized by adult mites or sequestered by adult mites from their fungal food. 

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