Amines formed by biosynthesis in germinated barley have been
suggested as precursors for N-nitrosodimethylamine (NDMA) in barley
malt dried by direct-fired kilning. This hypothesis was verified by
germinating raw barley and exposing the resulting malt roots and
clean malt to nitrous acid. Quantitation of the NDMA formed indicated
that malt roots contained relatively large amounts of NDMA precursor
which could only have been formed as a result of germination. The
clean malt also contained NDMA precursor, but the amount of precursor
in clean malt was only slightly higher than the level of precursor
already present in raw barley.
The two tertiary amine alkaloids, hordenine and gramine, which
are biosynthesized in malt during germination were subjected to nitrosation.
Nitrosation of both amines at 65° (pH 4.4 or pH 6.4) resulted
in NDMA formation. Gramine was highly susceptible to nitrosation to
yield NDMA. At 24° in dilute acetic acid (pH 3.4), the initial rate
of nitrosation of gramine to yield NDMA was nearly equal to the initial
rate of NDMA formation from dimethylamine. The ratio of initial
rates of formation of NDMA from gramine and trimethylamine was
6250:1. At 23°, the ratio of initial rates of formation of NDMA from
gramine and hordenine was 5200:1.
N-Methyltyramine and N-methyl-S-aminomethylindole, the immediate
biosynthetic precursors of hordenine and gramine, were synthesized.
Nitrosation of N-methyltyramine yielded p-hydroxy-N-nitroso-N-methyl-
2-phenylethylamine as the major reaction product and p-hydroxy-m-nitro-
N-nitroso-N-methyl-2-phenylethylamine as the minor product. Nitrosation
of N-methyl-3-aminomethylindole yielded N-nitroso-N-methyl-3-
aminomethylindole as the minor reaction product; the major product was
a dinitroso compound identified as N¹-nitroso-N-nitroso-N-methyl-3-
aminomethylindole.
Investigation of the products of hordenine nitrosation at 65°
(pH 4.4) indicated the formation of NDMA and p-hydroxy-m-nitro-N-nitroso-
N-methyl-2-phenylethyl amine; p-hydroxy-N-nitroso-N-methyl-2-
phenylethylamine was not observed as a product of hordenine nitrosation
at 65°. NDMA appeared to be the major nitrosamine formed from hordenine.
The rapid reaction of gramine with nitrous acid and investigation
of the gramine nitrosation reaction products both indicated that
gramine did not undergo nitrosation by the expected mechanism of nitrosative
dealkylation. A new mechanism is proposed to explain the rapid
reaction of gramine with nitrous acid and to account for the fact that
NDMA was the only N-nitrosamine formed during the nitrosation of
gramine. / Graduation date: 1983
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/26958 |
| Date | 01 October 1982 |
| Creators | Mangino, Mario M. |
| Contributors | Scanlan, Richard A., 1937- |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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