Modification of the amino acid sequence of a phenylpyruvate decarboxylase from Azospirillum brasilense produces a novel group of phenylpyruvate decarboxylases with improved specificity to certain substrates, including in particular C7-C11 2-ketoacids such as, for example, 2-ketononanoate and 2-keto-octanoate. This specificity enables effective use of the phenylpyruvate decarboxylase in, for example, an in vivo process wherein 2-ketobutyrate or 2-ketoisovalerate are converted to C7-C11 2-ketoacids, and the novel phenylpyruvate decarboxylase converts the C7-C11 2-ketoacid to a C6-C10 aldehyde having one less carbon than the 2-ketoacid. Ultimately, through contact with additional enzymes, such C6-C10 aldehydes may be converted to, for example, C6-C10 alcohols, C6-C10 carboxylic acids, C6-C10 alkanes, and other derivatives. Use of the novel genetically modified phenylpyruvate decarboxylases may represent a lower cost alternative to non-biobased approaches.