Alkaloids sharks

Much practical interest has arisen from steroidal alkaloids, called squalamines, from sharks of the western Atlantic coast (Chart 7.8.A/P/PO). Although imexceptional in structure, these steroids, as a rare example from higher organisms, are precursors or models for new drugs (Tables 13.3 and 15.1). 

Our knowledge of alkaloids in animals is scant. The so-called protoalkaloids (biogenic amines and their derivatives) are widespread in lower animals (194, 195), and the parallelism between plant and animal metabolism is extensive. Betaines, methylated purines (e.g., paraxan-thine (VI) ), derivatives of histidine (spinacine (VII) of the shark), and kynurenic acid (VIII) are not rare in animals. The animal alkaloids, with the exception of samandarine (Vol. V, p. 321), are characterized as weak bases this is perhaps of importance for their excretion. 

Alkaloids are basic, nitrogen-containing compounds of plant or animal origin, often having complex structures and significant pharmacological properties. Nicotine (from tobacco) and the amine obtained by deprotonation of squalamine (from sharks) are examples of alkaloids... 

Currently, there has been no study of the secondary metabolites of Cephalochordata. Studies of Urochordata have been considerable but have focused on the class Ascidiacea (ascidians or sea squirts), which contain entire series of alkaloids, often with antiviral and anti-tumor properties. The ascidians share with sharks, which are primitive cartilaginous fish, the absence of liability to tumor development. In many species there is no epibio-sis, which often indicates the presence of cytotoxic and/or antibacterial substances, but antiviral substances were discovered among ascidians with epibionts (Eudistoma sp. and eudistomins (see below). 

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