A new total synthesis of the mycotoxin ochratoxin A (OTA) is presented, in which it is prepared in 9% overall yield from commercially available substrates. The key step consists of the condensation reaction between protected L-phenylalanine and 5-chloro-8-hydroxy-3-methyl-1-oxoisochromane-7-carboxylic acid (ochratoxin α, OTα). The same strategy could be successfully applied to L-d5-phenylalanine, leading to the first total synthesis of d5-OTA, a molecular tracer for the detection and analytical quantification of the natural mycotoxin in food samples by means of stable isotope dilution assay (SIDA).