l‐Serine is the Direct Precursor for the Pyrazine Ring Construction in the Biosynthesis of 3‐Isobutyl‐2‐Methoxypyrazine in Bell Pepper Fruits (Capsicum annuum L.)

3‐Isobutyl‐2‐methoxypyrazine (IBMP) is an extremely potent odorant and responsible for the specific aroma of many fruits and vegetables. Especially bell pepper contains high levels of IBMP, which is the character impact compound of its typical aroma. However, since the discovery of methoxypyrazines in plants in the 1960s the biosynthesis of their pyrazine ring motif remained so far unknown. Therefore, the biosynthetic pathway to IBMP was investigated by feeding experiments with stable‐isotope labeled precursors. For the first time it could be shown that l‐serine plays a key role in the pyrazine ring construction of 3‐alkyl‐2‐methoxypyrazines (MPs). Based on HS‐SPME‐GCxGC‐TOF‐MS analysis, it is shown that the biosynthetic pathway to IBMP is closely linked to photorespiratory derived l‐serine. The biosynthetic pathway of 3‐isobutyl‐2‐methoxypyrazine (IBMP) was investigated in plants using in vivo feeding experiments with stable‐isotope labeled precursors. It has been demonstrated that photorespiratory derived l‐serine serves as a C2‐builing block and an N‐donor in IBMP‐biosynthesis.