Homotropane alkaloid

Anatoxin-a is a naturally occurring homotropane alkaloid produced by freshwater cyanobacteria of the genera Anabama (A. flos-ctquae and A. circinalis), Aphanizome-non, Cylindrospermum, Planktothrix, Microcystis aeruginosa [5-7], and Phormidium favosum [8]. Fatal intoxications have typically included cattle and birds [9], and, more recently, dogs [8] and flamingos [10]. 

Homobrassinolide (28-homoBL), 3862 Homocamptothecin, 652, 657, 666 Homocysteine (Hey), 3681-3683 Homoeostrichus sinclairii, 2895 Homoharringtonine, 1453 Homoisoflavonoids, 2163 Homologous genes, 686 Homomeric prenyltransferases, 2709 Homospermidine, 365 Homospermidine synthase (HSS), 365 Homoterpenes, 2915 Homotropane alkaloid, 43 Homovanillic, 2476... 

In most cases of secondary protection of insect herbivores by alkaloids the source of the alkaloid is the herbivore diet, i.e. the plant host. There have been several interesting reports on the occurrence of chemical defenses of insects based on alkaloids actively synthesized or at least chemically modified by the insect. One such report showed that deterrence to predation by ants and spiders was afibrded to the Mexican bean beetle Epilachna varivestis) by the production of the homotropane alkaloid euphococcinine (66). This compound which actually may be a polyketide, is not present in the body of larvae or newly hatched adults but is accumulated in the beetles blood within one week of emergence. When attacked, the beetle reflex-bleeds emitting droplets of blood containing as much as 5 pg of euphococcinine. 

Hyperaspine (23) is the first 3-oxaquinolizidine alkaloid reported so far from ladybird beetles. Its skeleton, however, which is based on a chain of 13 carbon atoms, is biosynthetically related to those of the homotropane and perhydroazaphenalene alkaloid already isolated from ladybirds [38]. 

Anatoxin-a, the first highly potent cyanotoxin to have its structure and absolute stereochemistry elucidated, was originally isolated from a unialgal clone of Anabaena Jlos-aquae (NRC-44h) [5]. The structure was confirmed by X-ray crystallographic data for the N-acetyl derivative [11] and additional studies have since provided further proof for the structure and stereochemistry (for example, [12]). Anatoxin-a is an unsymmetrical bicyclic secondary amine, and was the first naturally occurring alkaloid discovered to contain a 9-azabicyclo[4,2,l]nonane (homotropane) skeleton. Homotropanes are one-carbon analogs of the tropanes and, as such, are structurally closely related to the well-known alkaloid cocaine. 

Anatoxin-a is a bicyclic amine alkaloid (Figure 31.3). It contains a homotropane scaffold that is derived from glutamic acid. It is chiral, with two S5unmetric centers (Wonnacott and Gallagher, 2006). Only the (-l-)-anatoxin-a enantiomeric form is naturally produced, and the pKg of this form, at 9.4, indicates that it is mostly in the pro-tonated form under typical environmental pH conditions... 

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