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New heavy labelled auxins for mass spectrometry

The preparation of labelled derivatives of indole-3-acetic acid (IAA) is important for the standardization of mass spectrometry techniques. We are focused on the synthesis of IAA metabolites arising from [D5]-indole or [D5]-IAA as starting materials. In order to increase the number of isotopic atoms in the amino acid conjugates, N-15 labelled amino acids were used for the synthesis. The conjugates of [D5]-IAA with [N-15]-glycine, [N-15]-alanine, [N-15]-aspartic acid and [N-15]-glutamic acid were prepared by reaction of [D5]-IAA succinimide ester with the corresponding alpha-amino acid in alkaline medium. The aliphatic and aromatic N-15 labelled amino acids gave the conjugates via condensation of [D5]-IAA chloroformate anhydride with [N-15]-valine, [N-15]-leucine, [N-15]-isoleucine or [N-15]-phenylalanine in strongly alkaline medium. The same type of reaction was used for the preparation of [N-15]-indole-3-acetamide, where the mixed anhydride was poured into an aqueous solution of [N-15]-ammonia. Indole-3-ethanol and IAA-beta-D-glucosyl ester were labeled only in the indole ring. [D5]-indole-3-ethanol and [D5]-indole-3-methanol were prepared by reduction of either [D5]-IAA or [D5]-indole-3-carboxylic acid with lithium aluminium hydride.

heavy-isotope labelled auxin; amino acid conjugate; chemical synthesis; internal standard; mass spectrometry

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