Ochratoxin A labelled with ¹⁴C or ³H in the phenylalanine moiety

Abstract

SUMMARYOchratoxin A is a mycotoxin produced by Asperqillus and Penici1l.w moulds. The toxin is an amide formed between phenylalanine and the isocoumarin acid ochratoxin a .Ochratoxin A with high specific radioactivity can be obtained, by sub titution of the natural phenylalanine for I4C or %-labelled phenylalanine.Labelled ochratoxin A was formed by condensation of labelled phenylalanine ethylester with an anhydride derivative of ochratoxin a. The intermediate 0-acetyl ochratoxin C was hydrolysed with pig liver esterase and chymotrypsin to afford ochratoxin A. The overall yield of radioactivity was 50%. Specifi activi ies up to 500 Ci/mol and obtained.

Structures of Covalent Adducts between DNA and Ochratoxin A: A New Factor in Debate about Genotoxicity and Human Risk Assessment

“…All these factors compound the unsatisfactory design of the radiolabeled study, which, together with failure to have the planned positive control evidence of successful 32 P-postlabeling of parallel material in the Pfohl-Leszkowicz laboratory, fails to justify the claim of nongenotoxicity. The claim was also premature because substitution, of commercial 14 C phenylalanine for the corresponding unlabeled moiety in the 14 C-OTA prepared biosynthetically (21), by well-established methodology (22)(23)(24) was not done. Experiments described in ref 25 showed integrated findings on concentration of OTA in blood and ochratoxin R (OTalpha) in urine over a 2-week period of 5-day-a-week gavage dosing in vegetable oil.…”

Distribution of 14C‐Ochratoxin A in the Mouse Monitored by Whole‐Body Autoradiography

“…Radioactive ochratoxin A was synthesized from uniformly 14Clabeled phenylalanine (Amersham, England) (Hult 1986). The product was radioactively pure according to thin-layer chromotography (toluene-dioxane-acetic acid, 95:35:4) (Hult 1986) and the specific activity was determined to be 443 Ci/mol. A solution of I4C-ochratoxin A was prepared in 51 mM NaHC03.…”

“…The relative degree of blackening in different organs after 36 days' exposure has been compared with the blackening of a 14C-staircase represented by 213 (8192) and then forming a geometrical series with the next step half the strongest one, 2" (4096) and the next 2" (1048) and so on. extracts were chemically characterized by thin-layer chromatography on silica gel (Hult 1986).…”

“…extracts were chemically characterized by thin-layer chromatography on silica gel (Hult 1986). The relative degree of blackening in different organs after 36 days' exposure has been compared with the blackening of a 14C-staircase represented by 213 (8192) and then forming a geometrical series with the next step half the strongest one, 2" (4096) and the next 2" (1048) and so on.…”

Quantification of ochratoxin A in foods by a stable isotope dilution assay using high-performance liquid chromatography–tandem mass spectrometry

“…In the past there have been two attempts to synthesize radioactively labelled OTA to be used in metabolic studies [19,25]. Both approaches consisted of a metathesis by hydrolyzing OTA and subsequent coupling of the result- ing isocoumarin derivative ochratoxin ␣ (OT␣) to labelled l-phenylalanine.…”