Chromone alkaloids

The term chromone alkaloid is used to describe a structure consisting of a pyridine, piperidine, or pyrrolidine ring linked to the A ring of chromone (1). In... 

An anti-snake venom principle has recently been reported as a glycosidal quaternary chromone alkaloid named schumanniofoside 36 (14). Extracts of the stem bark were tested against the venom of the black cobra, Naja melanoleuca, in mice. The methanolic extract showed the greatest activity. This was fractionated and monitored to yield 36 as the active component. 

Besides leaves, roots are also a storage site for the accumulation of many interesting secondary metabolites such as anthraquinones, pre-anthraquinones, anthrones, chromones, alkaloids, flavonoids, conmarins. 

A review describing chromone alkaloids is available [600]. Four piperidine substituted chromones and their derivatives are described below. 

No studies have been carried out on the biogenesis of flavonoid and chromone alkaloids but there has been some success in the synthesis of some of the compounds included in this category. 

The only previously-published review of chromone alkaloids [1] covered both flavonoid and chromone alkaloids and both types are also included in this chapter. It will be seen that this is logical since, although any biogenetic link is not proven, the two groups can be produced by the same synthetic process and they also have some biological activities in common. Compounds mentioned in the first review are only mentioned here if further studies have been conducted on them or if they form the basis of the discovery or synthesis of novel compounds. 

Tables 1,2 summarise the compounds of this type so far isolated from the plant kingdom and it can be seen that there is no discernible pattern in the distribution of chromone alkaloids in the flowering plants. The flavonoidal alkaloids have been isolated from several different plant families but often only from one genus of a family. Many genera and species related to those yielding this type of alkaloid have not been investigated so further studies may enable patterns to be discerned.

Table I. Flavonoidal Chromone Alkaloids from Natural Sources...

The Meliaceae is known as a family that produces a variety of secondary metabolites, and even of alkaloidal types, so the occurrence of chromone alkaloids is not predictable. Indeed, chromone alkaloids have been reported from one species only of Dysoxylum whilst other species of the same genus produce a different type of alkaloid. The occurrence of tubastraine, a derivative of rohitukine, from a species of coral, emphasises the unpredictability of the occurrence of this type of compound [10]. 

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