Abstract: Nitrogen containing compounds may have formulas (I), (II) and (IV), and such compounds may be suitable for detecting alkyne group containing organic compounds by mass spectrometry. Furthermore, methods may also include synthesizing these compounds, detecting of organic compounds containing the specific compounds, uses of the compounds in mass spectrometry for determining enzyme activity or monitoring the lipid metabolism in a cell, and a kit which contains at least one of these compounds and at least one internal standard.

Abstract: This invention relates to an amino acid based on a naturally occurring non-polar, non-aromatic ?-amino acid, wherein said amino acid differs from the naturally occurring counterpart in that the side chain contains a diazirine ring. Furthermore provided are methods of synthesizing a (poly)peptide with one or more amino acids of the invention incorporated, methods for cross-linking interacting molecules, methods of synthesizing the amino acids of the invention, and a kit comprising the amino acids of the invention.