Alkaloid straight-chain

Coniine (12), impHcated by Plato in the death of Socrates, is the major toxic constituent of Conium maculatum L. (poison hemlock) and, as pointed out eadier, was apparendy the first alkaloid to be synthesized. For years it was thought that coniine was derived from lysine (24), as were many of its obvious relatives containing reduced piperidine nuclei and a side chain, eg, peUetierine (46). However, it is now known (99) that coniine is derived from a polyketooctanoic acid [7028-40-2] (138), CgH QO, or some other similar straight chain analogue. 

Aliphatic nitriles (—CH2CH2CH2CH2CN) (m/z 82, 96, 110, 124, 138, 152, etc., suggest straight-chain nitriles) Benzoquinones Piperidine alkaloids Some fluoroalcohols... 

We have recently characterized the heptacyclic alkaloid chilocorine from the ladybird (coccinellid) beetle Chilocorus cacti (23). In spite of its superficial complexity, this structure is easily dissected into two tricyclic moieties, A and B, each of which can be regarded as an acetogenin which has been elaborated from a straight chain of 13 carbon atoms stitched together at three points by a trivalent nitrogen atom. 

The phytochemicals that are discussed below may be divided Into three classical categories alkaloids, flavonolds, and terpenes. Straight chain carbon confounds, such as hydrocarbons, waxes, fatty acid and alcohols also occur In glands. The alkaloids tend to react as feeding deterents and as poisons (43). They are probably the major class found In any lists of plant toxins (44, 45). Flavonolds are well known antibacterial. 

In summary, the pumiliotoxin-A class alkaloids are unique to certain genera from four different families of amphibians. Pumiliotoxins and allo-pumiliotoxins often occur together. Homopumiliotoxins occur much less often. The unique and complex structures and the phylogenetic distribution of pumiliotoxin-A class alkaloids argue for the independent evolutionary development of a complex suite of biosynthetic enzymes. The branched-chain structures of the pumiliotoxin-A class also suggest the incorporation of isoprene units, unlike the preponderance of bicyclic den-drobatid alkaloids, which appear to be derived from straight-chain precursors. 

Indolizidine and quinolizidine alkaloids found in amphibians and ants were studied by Daly and co-workers who classified them in two different classes, A and B, Fig. (1) [2,15-17]. The former include 3,5- and 5,8-disubstituted indolizidines, 5,6,8-trisubstituted indolizidines and 1,4- and 4,6-disubstituted quinolizidines that can be derived from straight-chain carbon precursors. The latter contain one or more isoprene units, and include pumiliotoxins (PTX-A), allopumiliotoxins (a//o-PTX-A or... 

The pyrrolizidine alkaloids are not all poisonous. Schoental (42) has postulated that for an alkaloid to be toxic it must have a double bond between C-1 and C-2. The cyclic diesters are twice as toxic as the open diesters, and four times as toxic as the open monoesters. Esters of branched-chain acids are toxic while esters of straight-chain acids are not... 

Fig. 6.4 Branched-chain capsaicinoids, acid amide type alkaloids from Capsicum spp. all unsaturated acyl residues are tr

Table 7.5 Most frequent glycoalkaloids in the genus Solarium in the order of frequency listed all alkaloids with an occurrence in >2 species solacauUne added as a rare example for a straight chain (not branched) oligosaccharide moiety... 

The numbering system which is used throughout is that proposed by Wiesner (26) in his earlier review of the Lycopodium alkaloids. It is based on Conroy s polyacetate hypothesis of the biogenesis of these alkaloids from two straight-chain eight-carbon units (27). This system is applied in the formulas of Chart 1 which illustrates the principal ring systems known in this series. 

Hiraki, T, Yamagiwa, Y, and Kamikawa, T. (1995) Synthesis of a straight chain analog of penaresidins, azetidine alkaloids from marine sponge Penares sp. Tetrahedron Lett., 36, 4841-4844. 

Most pyrrolizidine alkaloids are esters constructed from an aminoalco-hol called a necine unit (pyrrolizidine derivative), and straight or branched chain fatty acid, called a necic acid. Necine is the derivative of pyrrolizidine, i.e., azabicyclo[3,3,0]octane, and a hydroxymethyl (-CH2OH) moiety is always attached at the C-1 position. Necines can be classified into two groups, either with or without a double bond between the C-1 and C-2 positions. The stereochemistry of the H-8 position is usually H-8a.When the C-8 position is oxidized, as in the case of otonecine, it becomes an eight-membered ring by decychzation. 

Recently a whole series of indolizidine and pyrrolo-indolizidine alkaloids have been found in Myrmicaria ants (Figure 9.12), which evidently have a similar origin to the indolizidines in Figure 9.10. Note that they are all constructed from straight carbon chains. The structures of the complex dimer and trimer were deduced from NMR and mass spectral studies. 

---