Colored compounds formed by Maillard-type reactions fromfuran-2-carboxaldehyde and primar
yand secondary amino acids inclu
ding SIZE="-1">L-alanine and
L-proline, respectively, have been identified.When furan-2-carboxaldehyde was heated with
L-prolinein aqueous solution at pH 7.0, an intenselyyellow compound was generated, which was identified as5(
S)-(2-carboxy-1-pyrrolidinyl)-2-hydroxy-(
E,
E)-2,4-pentadienal-(
S)-(2-carboxypyrrolidine)imine(
1) by application of several one- and two-dimen
sional NMR experiments and, in addition, by MS, UV, and IRspectroscopy. Further thermaltreatment of compound
1 resulted, upon a ring closurereaction, in the formation of(
E)-4,5-bis[(
S)-2-carboxy-1-pyrrolidinyl]-2-cyclopenten-1-one (
5), which hasbeen, to our knowledge, as yet notreported in the literature. To confirm the proposed structures,
L-proline was substituted bypyrrolidine and piperidine, lea
ding to analogous
N-c
yanines(
2 and
3) and cyclopentenones (
4and
6). On the other hand, thermal treatment of an aqueoussolution of furan-2-carboxaldehyde and
L-alanine led to the formation of the novel red compounds
8a and
8b, which were identified as(
S)-4-[(
E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(
E)-(2-furyl)methylidene]-2,3-dihydo-
-amino-3-oxo-1
H-pyrrole-6-acetic acid and the correspon
ding2-(
Z)-(2-furyl)methylidene isomer. This isthefirst time that chromophoric compounds compri
sing four linked ringswith an amino acid moietyincorporated were identified in a Maillard reactionsystem.Keywords: Nonenzymatic browning; Maillard reaction; furan-2-carboxaldehyde;alanine; proline;(
S)-4-[(
E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(
E)-(2-furyl)methylidene]-2,3-dihydro-
-amino-3-oxo-1
H-pyrrole-1-acetic acid
