“…By means of these deduction techniques most of the important proline-and hydroxyproline-derived products are confirmed due to their hitherto proposed formation pathways. The labeling experiments support the expected l-deoxydiketose route leading to cyclotene via hexose reductone from the intact carbon chain of glucose and prove true an -dicarbonyl cleavage (Simon and Heubach, 1965;Hayase and Kato, 1986) to form unlabeled cyclopenta[6]pyridinone and 2-propionylpyridine derivatives. Maltoxazine, the important guide com-ponent of malt, wort, and beer , is proved to be generated from the intact glucose carbon chain via 3-deoxyaldoketose, whereas the so far supposed closely related formation of tentatively characterized 5-(l-hydroxyethylidene)-l,2,3,4,5,6-hexahydro-7H-cyclopenta[b]pyridin-7-one (Helak et al, 1989b) is disqualified by this method.…”