Nitrile-glucosides

Seigler, D. S. and A. M. Brinker, Characterization of cyanogenic glycosides, cyanolipids, nitroglycosides, organic nitro compounds and nitrile glucosides from plants, in Modem Methods... 

Forslund K, Morant M, Jorgensen B, Olsen CE, Asamizu E, Sato S, Tabata S, Bak S (2004) Biosynthesis of the nitrile glucosides rhodiocyanoside A and D and the cyanogenic glucosides lotaustralin and linamarin in Lotus iaponicas. Plant Physiol 135 71-84... 

Hydrocyanic acid, HCN, also known as prussic acid, or formo-nitrile, is the product of decomposition of numerous glucosides found in a very large number of plants, usually together with some other volatile compound, so that essential oils containing hydrocyanic acid do not, for practical purposes, exist in the first instance as such in the plant, but are only developed on the decomposition of the glucoside. 

Figure 13.2 Biosynthetic pathways of (A) cyanogenic glucosides and (B) glucosinolates. The CYP79s are assumed to catalyze the same reaction in both pathways. It is not known whether the oxime is oxidized to an aci-nitro compound or a nitrile oxide in the glucosinolate pathway.

Owing to the Curtin-Hammett principle, the ratio of the iodonium intermediates 39 and 40 does not reflect the distribution of the conformers in 38 (5H4 4H5 = 95 5). Thus, both the 2-deoxy-2-iodo-ot-mannoside 50 and the 2-deoxy-2-iodo-P-glucoside 51 are formed in almost equimolar amounts. Similar results are observed in glycals with nitrile or carboxamide functions [11]. 

Due to homologies in structures and biosynthesis, some minor groups of natural products seem to be related to cyanogenic glucosides. These compounds, i.e. cyanogenic lipids, nitrile- and nitro-compounds, are briefly presented in this chapter. 

Tapper, B.A. and Butler, G.W. (1971) Oximes, nitriles and 2-hydroxynitriles as precursors in the biosynthesis of cyanogenic glucosides. Biochem.., 124, 935-41. 

The intact glucosides are probably not the active agents, but rather the isothiocyanates, thiocyanates, and nitrile derivatives derived from them. The initial hydrolysis products are thiohydroximate 0-sulfonates, which are followed by rearrangements to give isothiocyanates, and, under some conditions, nitriles and thiocyanates are also formed (Dewick, 1984). In contrast to the intact glucosinolates, most of the hydrolysis products are relatively volatile (Fig. 17.6). 

The above-mentioned plants, as Brassicacea, contain mustard oil glucosides (glucosinolates, cf. 17.1.2.6.5) which, immediately after seed crushing, are hydrolyzed to esters of isothio-cyanic acid. The hydrolysis is dependent on seed moisture and is catalyzed by a thioglucosidase enzyme called myrosinase (EC 3.2.3.1). In the presence of the enzyme, some of the isocyanates are isomerized into thiocyanates (esters of normal thiocyanic acid or rhodanides) and, in part, are decomposed into nitrile compounds which do not contain sulfur. All these compounds are volatile and, when dissolved in oil, are hazardous to health and detrimental to oil flavor. Moreover, they interfere with hydrogenation of the oil by acting as Ni-catalyst poisons (cf. 14.4.2.2). Therefore, in the production of rapeseed oil, a dry conditioning step is used (without live steam) to... 

---