Laetrile, the bogus ‘vitamin B₁₇’

Abstract

The name ‘laetrile’ was coined by Ernst Krebs, Jr. as a condensation of laevorotatory aminonitrile β-glucuronic acid¹. The term laetrile as presently used refers to any one of a group of compounds that include amygdalin, prunasin, linamarin, and dhurrin. These compounds are correctly called ‘cyanogenic glycosides.’ The laetrile that is being used illicitly to treat cancer is amygdalin, a β-glucoside containing gentiobiose and the cyanhydrin, mandelonitrite, formed by condensation of benzaldehyde and hydrocyanic acid (HCN)². Its structural formula is shown in Figure 1 from Conn³. Liebig and Wohler in 1837, described the hydrolysis of amygdalin by an enzyme they called ‘emulsin’ (actually, a mixture of enzymes) present in almonds to yield benzaldehyde, glucose and HCN (cyanide). These products are shown in Figure 1. The other cyanogenic glycosides all contain HCN, condensed with a ketone or aldehyde, and a carbohydrate in β-linkage. A list of some of these is shown in Table 1 taken from Conn².