Unambiguous structure of the compounds in the reaction of L-tryptophan and 5-hydroxy-l-tryptophan with alkyl isocyanates in acetone

On the basis of X-ray crystallographic analysis, it is shown that the reaction of L-tryptophan and 5-hydroxy-L-tryptophan with alkyl isocyanates in acetone affords, in agreement with Claesson's work, 3-alkylcarbamoyl-4-(3-indolylmethyl)-1,3-oxazolidin-5-ones 2 and not 2-(3-alkyl-4,4-dimethyl-2-oxo)-1,3-diazetidinyl]-3-(3-indolyl)propionic acids 1 as previously proposed.