chapter 2 . CHAPTER 2 CHAPTER Chemical and physical characteristics of the principal mycotoxins Summary try number : 1162-65-8. Molecular formu- Aflatoxin M1. CA name : (6aR,9aR)- la : C17H12O6. Molecular weight : 312.3. 2,3,6a,9a-tetrahydro-9a-hydroxy-4- This chapter provides information Aflatoxin B2. CA name : (6aR,9aS)- methoxycyclopenta[c]furo-(3′,2′:4,5]- about the chemical and physical 2,3,6a,8,9,9a-hexahydro-4-methoxy- furo[2,3-h][l]benzopyran-1,11-dione. properties of the mycotoxins consid- cyclopenta[c]furo(3′,2′:4,5]furo[2,3-h]- CAS registry number : 6795-23-9. ered in this book: aflatoxins; fumonisins; [l]benzopyran-1,11-dione. CAS registry Molecular formula : C17H12O7. Molec- ochratoxin A; trichothecenes, espe- number : 7220-81-7. Molecular formula : ular weight : 328.3. cially deoxynivalenol and nivalenol; C17H14O6. Molecular weight : 314.3. Structures of aflatoxins are shown zearalenone; and ergot alkaloids. This Aflatoxin G1. CA name : (7aR,10aS)- in Fig. 2.1. information about structures reveals 3,4,7a,10a-tetrahydro-5-methoxy-1H, the chemical diversity of mycotoxins, 12H-furo-(3′,2′:4,5]furo[2,3-h]pyrano- 1.2 Physical data which is relevant to the wide range of [3,4-c][l]benzopyran-1,12-dione. CAS toxicological effects in animals and registry number : 1165-39-5. Molecular Descriptions. Colourless to pale- humans discussed later in the book. formula : C17H12O7. Molecular weight : yellow crystals. Fluorescence in ultra- 328.3. violet (UV) light : aflatoxins B1 and 1. Aflatoxins Aflatoxin G2. CA name : (7aR,10aS)- B2, blue; aflatoxins G1 and G2, green; 3,4,7a,9,10,10a-hexahydro-5-methoxy- aflatoxin M1, blue–violet. 1.1 Formulae and structures 1H,12H-furo-(3′,2′:4,5]furo[2,3-h]pyrano- Melting-points. See Table 2.1. [3,4-c][l]benzopyran-1,12-dione.CAS Spectral properties. For UV ab- Aflatoxin B1. Chemical Abstracts (CA) registry number : 7241-98-7. Molecular sorption, see Table 2.1. Fluorescence name : (6aR,9aS)-2,3,6a,9a-tetrahydro- formula : C17H14O7. Molecular weight : excitation and emission data are 4-methoxycyclopenta[c]furo-(3′,2′:4,5]- 330.3. not listed in Table 2.1 because they furo[2,3-h][l]benzopyran-1,11-dione. depend on the type of instrument, the Chemical Abstracts Service (CAS) regis- solvent, and the supporting media Chapter 2. Chemical and physical characteristics of the principal mycotoxins 31 Fig. 2.1. Structures of aflatoxins Fumonisin B2. CA name : 1,2,3- propanetricarboxylic acid, 1,1′-[1-(12- amino-9,11-dihydroxy-2-meth- yltridecyl)-2-(1-methylpentyl)-1,2- ethanediyl] ester. CAS registry number: 116355-84-1. Molecular formula: C34H 59NO14. Molecular weight : 705. Structures of fumonisins are shown in Fig. 2.2. 2.2 Physical data Unless otherwise noted, data are from WHO (2000). Description. White hygroscopic powder. Melting-point. Not known (com- pounds have not been crystallized). Spectral properties. For mass and NMR spectral data, see Bezuidenhout et al. (1988), Laurent et al. (1989), Plattner et al. (1990), Savard and Blackwell (1994), and Cole et al. (2003a). used. For those data, see Wogan Stability. Unstable to UV light in 2.3 Chemical data (1966), Robertson and Pons (1968), the presence of oxygen. Unstable to Kiermeier and Kroczek (1974), and extremes of pH (< 3 or > 10). Unstable Solubility. Soluble in methanol, in ace- Uwaifo et al. (1977). in the presence of oxidizing agents tonitrile–water, and in water (at least For mass and nuclear magnetic (Castegnaro et al., 1980, 1991). 20 g/L) (NTP, 2001). resonance (NMR) spectral data, see Reactivity. Under alkaline condi- Stability. Stable in acetonitrile– Bycroft et al. (1970), Stubblefield et tions, the lactone ring opens and the water (1:1) at 25 °C. Unstable in meth- al. (1970), and Cole and Schweikert aflatoxins are apparently absent. anol at 25 °C, forming monomethyl (2003). However, the reaction is reversible and dimethyl esters (Gelderblom Specific rotation. [α]D in chloro- upon acidification. et al., 1992; Visconti et al., 1994). form, –558° (aflatoxin B1), –430° Ammoniation at high temperature Stable in methanol at –18 °C (aflatoxin B2), –556° (aflatoxin G1), and high pressure opens the lactone (Visconti et al., 1994). Stable in –473° (aflatoxin G2); [α]D in dimeth- ring and results in decarboxylation. buffer solutions over the pH range ylformamide, –280° (aflatoxin M1) This reaction is not reversible. 4.8–9 at 78 °C (Howard et al., 1998). (Cole and Schweikert, 2003). Octanol – water partition coeffi- 2. Fumonisins cient for fumonisin B1. log P = 1.84 1.3 Chemical data (Norred et al., 1997). 2.1 Formulae and structures Solubility. Insoluble in non-polar 3. Ochratoxin A solvents. Slightly soluble in water Fumonisin B1. CA name : 1,2,3-propane- (10–20 µg/mL). Freely soluble in tricarboxylic acid, 1, 1′-[1-(12-amino- 3.1 Formula and structure moderately polar organic solvents 4,9,11-trihydroxy-2-methyltridecyl)-2- (e.g. chloroform, methanol), espe- (1-methylpentyl)-1,2-ethanediyl] ester. Ochratoxin A. CA name : N-[(5-chlo- cially in dimethyl sulfoxide (Cole and CAS registry number : 116355-83-0. ro-3,4-dihydro-8-hydroxy-3-methyl-1- Cox, 1981; O’Neil et al., 2001). Molecular formula : C34H59NO15. Molec- oxo-1H-2-benzopyran-7-yl)carbonyl]-L- ular weight : 721. phenylalanine. CAS registry number: 32 Table 2.1. Melting-points and ultraviolet absorption of aflatoxins Ultraviolet absorption Aflatoxin Melting-point (°C) –1 –1 –3 λmax(nm) ε (L.mol .cm ) × 10 B1 268–269 (decomposition) 223 25.6 (crystals from CHCl3) 2 CHAPTER 265 13.4 362 21.8 B2 286–289 (decomposition) 265 11.7 (crystals from CHCl3–pentane) 363 23.4 G1 244–246 (decomposition) 243 11.5 (crystals from CHCl3–methanol) 257 9.9 264 10.0 362 16.1 G2 237–240 (decomposition) 265 9.7 (crystals from ethyl acetate) 363 21.0 M1 299 (decomposition) 226 23.1 (crystals from methanol) 265 11.6 357 19.0 Data from O’Neil et al. (2001). Fig. 2.2. Structures of fumonisins Chapter 2. Chemical and physical characteristics of the principal mycotoxins 33 303-47-9. Molecular formula : C 20H18ClNO6. medium (Subirade, 1996; Van der When DON was gamma- Molecular weight : 403.8. Stegen et al., 2001). irradiated on maize, breakdown of The structure of ochratoxin A Reactivity. The lactone ring DON began only after irradiation to (OTA) is shown in Fig. 2.3. opens under alkaline conditions, but 20 kGy, and 80–90% of the DON the reaction is reversible. Solutions remained after irradiation to 50 kGy 3.2 Physical data of OTA are completely degraded by (O’Neill et al., 1993). treatment with an excess of sodium No significant decomposition of Description. White odourless crys- hypochlorite. DON was observed when stored in talline solid (Pohland et al., 1982). ethyl acetate for 24 months at 25 °C Intensely fluorescent in UV light, 4. Deoxynivalenol or 3 months at 40 °C (Widestrand emitting green and blue fluorescence and Pettersson, 2001). DON was in acid and alkaline solutions, 4.1 Formula and structure relatively stable in buffer solutions respectively, due to two different over the pH range 1–10 (Lauren and forms, i.e. closed or open lactone Deoxynivalenol. CA name: 12,13-ep- Smith, 2001). ring, respectively. oxy-3,7,15-trihydroxy-(3α,7α)-trichothec- Melting-point. 159 °C when re- 9-en-8-one. CAS registry number: 5. Nivalenol crystallized from benzene–hexane 51481-10-8. Molecular formula: C15H20O6. (Natori et al., 1970); 169 °C when Molecular weight: 296.32. 5.1 Formula and structure recrystallized from xylene (Van der The structure of deoxynivalenol Merwe et al., 1965a, 1965b); 168– (DON) is shown in Fig. 2.4. Nivalenol. CA name : 12,13-epoxy- 173 °C after drying for 1 hour at 60 °C 3,4,7,15-tetrahydroxy-(3α,4β,7α)-tricho- (Pohland et al., 1982). 4.2 Physical data thec-9-en-8-one. CAS registry num- 20 Specific rotation. [α] D –118° (c = ber : 23282-20-4. Molecular formula : 1.1 mmol/L in chloroform) (Van Description. White needles. C15H20O7. Molecular weight : 312.32. der Merwe et al., 1965a, 1965b); Melting-point. 151–153 °C. The structure of nivalenol (NIV) is 21 20 [α] D –46.8° (c = 2.65 mmol/L in Specific rotation. [α] D +6.35° (c = shown in Fig. 2.4. chloroform) (Pohland et al., 1982). 0.07 mmol/L in ethanol). UV spectrum. At λmax of 214, 282, Spectral properties. IR, UV, 5.2 Physical data and 332 nm, extinction coefficients of NMR, and mass spectral data have –3 –3 37.2 × 10 , 0.89 × 10 , and 63.3 × been reported (Cole and Cox, 1981; Description. White crystals. –3 . –1. –1 10 L mol cm , respectively, have Cole et al., 2003c). Melting-point. 222 –223 °C (with been reported (Cole and Cox, 1981). decomposition, after drying in the pres- Other spectral properties. For 4.3 Chemical data ence of P2O5 at reduced pressure). 20 infrared (IR) spectra, see Van der Specific rotation. [α] D +21.54° (c = Merwe et al. (1965a, 1965b), Steyn Solubility. Soluble in chloroform, 1.3 mmol/L in ethanol). and Holzapfel (1967), and Pohland ethanol, methanol, and ethyl acetate. Spectral properties. IR, UV, NMR, et al. (1982). For NMR spectra, see Stability. Autoclaving creamed and mass spectral data have been Pohland et al. (1982) and Cole et maize reduced DON content by only reported (Cole and Cox, 1981; Brumley al. (2003b). For mass spectra, see 12% (Wolf-Hall et al., 1999). At pH et al., 1982; Cole et al., 2003c). Pohland et al. (1982) and Cole et al.