The principal pathway for monoterpene biosynthesis in peppermint. The responsible enzymes are: geranyl diphosphate synthase (1), (4S)-(−)-limonene synthase (2), cytochrome P450 (−)-limonene-3-hydroxylase (3), (−)-trans-isopiperitenol dehydrogenase (4), (−)-isopiperitenone reductase (5), (+)-cis-isopulegone isomerase (6), (+)-pulegone reductase (7), and (−)-menthone reductase (8).