Nitriles from glucosinolates

NASTRUZZI C, CORTESI R, ESPOSITO E, MENEGATTI E, LEONI O, lORI R and PALMIERI S (2000) In vitro antiproliferative activity of isothiocyanates and nitriles generated hy myrosinase-mediated hydrolysis of glucosinolates from seeds of cruciferous vegetables , JAgric Food Chem, 48 3572-5. 

Figure 13.1 Degradation of glucosinolates. Hydrolysis is catalyzed by myrosinases and gives rise to different degradation products dependent on the structure of the glucosinolate side chain and the hydrolysis conditions. (I) isothiocyanates, the major product at pH >7 (II) nitriles, the major product at pH <4 (ID) thiocyanates, produced from 2-propenyl-, benzyl-, and 4-methylthiobutylglucosinolates (IV) oxazolidine-2-thiones, produced from glucosinolates with P-hydroxylated side chains, (V) epithionitriles, produced in the presence of epithiospecifier proteins.

Burow M, Marker J, Gershenzon J, Wittstock U (2006) Comparative biochemical characterization of nitrile-forming proteins from plants and insects that alter myrosinase-catalysed hydrolysis of glucosinolates. FEES J 273 2432-2446... 

Bellostas N, Sorensen AD, Sorensen JC, Sorensen H (2008) Fe2-l-catalyzed formation of nitriles and thionamides from intact glucosinolates. J Nat Prod 71 76-80 Stevens JF, Reed RL, Alber S, Pritchett L, Machado S (2009) Herbicidal Activity of glucosinolate degradation products in fermented meadowfoam Limnanthes alba) seed meal. J Agric Food Chem... 

Protein-rich rape seed residues from biodiesel production plants are rich in phenolic compounds, glucocinolates and phytic acid. Phenolic compounds and phytic acid could be used as potent antioxidants in cosmetic and pharmaceutical formulations (Shamsuddin, 1995 Amarowicz and Shahidi, 1994 Wanasundara et al., 1996 Oatway et al., 2001). Derivatives from glucosinolate hydrolysis, including isothiocyanates, thiocyanates and nitriles, could be used as anticarcinogenic agents, biopesticides and flavour compounds (Halkier and Gershenzon, 2006). 

A major proportion of the glucosinolate hydrolysis products formed upon myrosinase cleavage in some plants are nitriles. In vitro, nitrile formation associated with myrosinase-catalyzed hydrolysis is enhanced at low pH (pH<3) and in the presence of ferrous ions. In vivo, protein factors in addition to myrosinase may be responsible for nitrile formation. If the glucosinolate side chain has a terminal double bond, the sulfur released from the thioglucosidic bond may be captured by the double bond and an epithionitrile is formed.9 This reaction takes place only in plants that possess a protein factor known as epithiospecifier protein (ESP). ESP activities have been identified in several species of the Brassicaceae and shown to influence the outcome of the myrosinase-catalvzed hydrolysis reaction although they have no hydrolytic activity by themselves.10 12 The mechanism by which ESPs promote epithionitrile formation is not known. 

Few studies have directly compared the effects of different hydrolysis products derived from the same glucosinolate. Such comparative studies with insects are listed in Tables 5.1-3, and comparative studies with other organisms in Table 5.4. In many cases, isothiocyanates seem to have greater biological activity than nitriles, thiocyanates, and oxazolidine-2-thiones. However, comparisons are complicated by differences among the hydrolysis products in physico-chemical properties, such as volatility. If two hydrolysis products differ significantly in volatility, for example,... 

Table 5.4 Examples of studies comparing effects of different hydrolysis products derived from die same glucosinolate. NCS, isothiocyanate CN, cyanide (= nitrile).

---