Salicin Salicylaldehyde

Myrmica rubra show that salicylaldehyde is a more potent deterrent that salicin (63) or its aglycone saligenin (83), The eggs of some of the beetles that feed on members of the Salicaceae contain salicin. Salicylaldehyde is detected in neonate larvae, suggesting that salicin is quickly converted to the aldehyde (Pasteels et al., 1986 Rowell-Rahier and Pasteels, 1986). This shift to members of the willow family appears to have occurred at least three times independently. The species that shifted are able to exploit a food source, yet are well protected. The larvae are provided with an additional method of defense the adults are able to sequester sufficient salicin in the eggs to make them potentially lethal to ants and to provide protection for the neonate larvae (Pasteels et al., 1986, 1988, 1989 Rowell-Rahier and Pasteels, 1986). 

SAM-dependent methylation of salicylic acid. The salicyl alcohol derivative salicin, found in many species of willow (Salix species Salicaceae), is not derived from salicylic acid, but probably via glucosylation of salicylaldehyde and then reduction of the carbonyl (Figure 4.27). Salicin is responsible for the analgesic and antipyretic effects of willow barks, widely used for centuries, and the template for synthesis of acetylsalicylic acid (aspirin) (Figure 4.27) as a more effective analogue. 

Another active principle soon extracted from plants was salicylic acid. Willow and salicin, in extensive competition with Cinchona bark and quinine, never became a very popular treatment for fever or rheumatic symptoms due to a Scottish physician, Thomas John MacLagan (1838-1934), who launched salicin in 1876. His rationale was inspired by the Paracelse signature s theory willow is growing in moisture along rivers and lakes, an ideal place to be crippled with rheumatism. Raffaele Piria (1815-1865), after isolation of salicylaldehyde (1839), in Spireae species, prepared salicylic acid from salicin. This acid was easier to use and was an ideal step before future synthesis. His structure was closely related to that of benzoic acid, an effective preservative usefiil as an intestinal antiseptic, for instance in typhoid fever. Patients treated with salicylic acid were dying as frequently as untreated patients, but without fever. 

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