Ultraperformance liquid chromatography coupled with negative electrospray tandem mass spectrometry (UPLC-ESI-MS/MS) was used to determine 7 hydroxy fatty acids in the pollen of Brassica campestris L. var. oleifera DC. All the investigated hydroxy fatty acids showed strong deprotonated molecular ions [M–H]？, which underwent two major fragment pathways of the allyl scission and the β-fission of the alcoholic hydroxyl group. By comparison of their molecular ions and abundant fragment ions with those of reference compounds, they were tentatively assigned as 15,16-dihydroxy-9Z,12Z-octadecadienoic acid (1), 10,11,12-trihydroxy-(7Z,14Z)-heptadecadienoic acid (2), 7,15,16-trihydroxy-9Z,12Z-octadecadienoic acid (3), 15,16-dihydroxy-9Z,12Z-octadecadienoic acid (4), 15-hydroxy-6Z,9Z,12Z-octadecatrienoic acid (5), 15-hydroxy-9Z,12Z- octadecadienoic acid (6), and 15-hydroxy-12Z-octadecaenoic acid (7), respectively. Compounds 3, 5, and 7 are reported for the first time. 1. Introduction Pollen contains many kinds of nutrient which are necessary to human body. It is well known as a natural nutrition, health food, and “perfect food.” The pollen preparation (Qian Lie Kang Tablets) made of Brassica campestris L. var. oleifera DC. has also been widely used in China as a good treatment for benign prostatic hyperplasia (BPH), and a chemical study has found plenty of fatty acids in the pollen [1]. Reports have shown promising therapeutic effects of fatty acids and their derivatives in treatment of BPH [2–6]. Hydroxy fatty acids contained in pollen are important bioactive substances. Various kinds of hydroxy fatty acids exhibit many pharmacological activities such as antitumor, antifungal, and prostaglandin E-like [7–9]. Although the pollen preparation has been used as phytotherapy for BPH for a long time, its active components and mechanism of action remain unclear. The effects of the supercritical fluid extract and its residue of the plant were screened so as to clarify its active constituents, and its supercritical fluid extract decreased the size of the prostate of androgen-induced prostatic rats by in vivo experiments and also demonstrated remarkable inhibitory effects on 5 -reductase and aromatase through in vitro experiments. The chemical investigation of its supercritical fluid extract has led to the isolation of some fatty acids and fatty acid derivatives [10], and the activity test experiments showed that fatty acids possessed strong inhibitory activity on 5 -reductase, which were consistent with literature reports [2–4]. The activity test experiments also displayed
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