Preparation of labelled compounds by biosynthesis

Biosynthetic methods are of importance in the preparation of natural products and related compounds [60]. The requirements of such methods are that a system must be devised that not only produces the desired product, but produces it in a readily isolable form. 

More specific labelling may be obtained in a biosynthetic process using enzymic methods of synthesis. The preparation of amino acids by the reductive amination of 2-keto acids is well known. Indeed, the synthesis of N-labelled amino acids by this route is among the earliest literature on the preparation of compounds labelled with stable isotopes [73], Such reductions can be carried out enzymically and L - [a- N] glutamic acid has been prepared in good yield from 2-oxoglutaric acid and N-labelled ammonium chloride in the presence of reduced nicotinamide adenine dinucleotide phosphate [74], 

As will be clear from a subsequent section, a number of antibiotics labelled with stable isotopes have been prepared in studies of their biosynthesis from labelled precursors. 

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