Characterization of two unknown compounds in methanol extracts of rosemary oil

In this study, two unknown compounds in rosemary oil, containing 3% carnosic acid and 0.3% carnosol, were identified and characterized. After methanol extraction, purification, and analysis by reversed-phase HPLC and LC-MS, a recovery of 92% (+/-8%) of carnosic acid was obtained, but no carnosol was found. However, two unknown compounds with a molecular weight of 330.2 and 302.2 were consistently detected. From additional LC-MS-MS, (1)H NMR, and elemental analyses, it became clear that the first compound (M(w) = 330.2) could not be carnosol. It was hypothesized that it originated from the breakdown of the intramolecular bond of carnosol, followed by the addition of a water molecule. Possibly, an unsaturated double bond was formed after dehydration. Assuming that this compound was an intermediate in the conversion to rosmanol, the second unknown compound (M(w) = 302.2) may have resulted from the breakdown of the intramolecular bond of rosmanol. Similarly, an unsaturated double bond may have been formed. After splitting off carbon oxide, a detectable molecule with a molecular weight of 302.2 was observed.