β-Carbolines are naturally
occurring bioactive alkaloids.
In this work, carbohydrate-derived β-carbolines (βCs),
1-(1,3,4,5-tetrahydroxypent-1-yl)-β-carboline isomers (
1a/b
), 1-(1,4,5-trihydroxypent-1-yl)-β-carboline (
2
), 1-(1,5-dihydroxypent-3-en-1-yl)-β-carboline (
3
), and 1-(1,2,3,4,5-pentahydroxypent-1-yl)-β-carboline
(
4
) were identified and analyzed in commercial foods.
The concentrations of βCs
1–4
in foods ranged
from undetectable to 11.4 μg/g levels, suggesting their intake
in the diet. Processed foods contained higher amounts than fresh or
unprocessed foods, and the highest content was found in processed
tomato and fruit products, sauces, and baked foods. βCs
1–3
were formed in foods during heating, and
1a/b
were the main compounds. The formation of carbohydrate-derived
βCs was studied in model reactions of tryptophan and carbohydrates.
They formed in reactions of tryptophan with glucose under acidic conditions
at temperatures higher than 80 °C. The formation of
1a/b
was favored, but
2–3
increased at high temperatures.
Noticeably, the βCs
1–3
formed in the reactions
of tryptophan with fructose or sucrose, and the formation from fructose
was much higher than from glucose. Thus, fructose was the main carbohydrate
involved in the formation of
1–3
, whereas sucrose
gave these βCs after acid hydrolysis. It is shown for the first
time that the mechanism of formation of βCs
1–3
occurs from the sugar intermediate 3-deoxyglucosone that reacts
with tryptophan affording these carbohydrate-derived βCs. A
mechanism of reaction to give βCs
1–3
is
proposed that relies on the tautomerism (keto–enediol or enamine–imine)
of intermediates involved in the reaction. Carbohydrate βCs
1–4
were assessed as inhibitors of monoamine oxidase
(MAO), as antioxidants, and for their interaction with DNA. They were
not good inhibitors of MAO-A or -B, were poor antioxidants, and did
not appreciably interact with DNA.
