Formation of 1-Alkyl-5-(hydroxymethyl)pyrrole-2-aldehydes in the Browning Reaction between Hexoses and Alkylamines

d-Glucose and butyl-, ethyl-, or methyl-amine were reacted at 100°C or 70°C in an aqueous or methanol solution neutralized with acetic acid to obtain browning reaction products, and the formation of N-substituted 5-(hydroxymethyl)pyrrole-2-aldehydes in the reaction was investigated.

At first, the reaction products were treated with 2,4-dinitrophenylhydrazine reagent and the resulting 2,4-dinitrophenylhydrazones (2,4-DNPs) were fractionated by column chromatography to isolate crystalline 2,4-DNPs. When the products obtained from d-glucose and butylamine were treated with the reagent consisting of 2,4-dinitrophenylhydrazine, sulfuric acid, water and either ethanol or methanol, 2,4-DNP of l-butyl-5-(ethoxymethyl or meth-oxymethyl)pyrrole-2-aldehyde (I or II) was isolated. In this formation ethanol or methanol was considered to be directly involved. On the other hand, 2,4-DNP of 5-hydroxymethyl derivative (III) was not detected, even when the reagent containing water alone as a solvent was used.

Secondly, in order to isolate the free pyrrolealdehyde, the above browning reaction products were extracted with ethyl acetate and the extract was chromatographed on a silica gel column. From the main carbonyl fraction was isolated 1-butyl-, ethyl-, or methyl-5-(hydroxymethyl)-pyrrole-2-aldehyde (III, IV, or V), which was characterized by elementary analyses and ultraviolet, infrared, and nuclear magnetic resonance spectra.