冰片（分子式：C10H18O），又名片腦、桔片、龍腦香、梅花冰片、羯布羅香、梅花腦、冰片腦、梅冰、龍腦、瑞腦、腦子、天然冰片、老梅片、梅片等，是由2個異戊二烯結構單元組成的環狀化合物，屬於單萜衍生物[1]。根據旋光性分為左旋龍腦和右旋龍腦[2]。右旋龍腦主要來源於龍腦樟和陰香樹[3]，而左旋龍腦主要來源於菊科植物[4]。
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冰片的合成前體由細胞質中的甲羥戊酸途徑和質體中的4-磷酸-2-甲基赤蘚糖途徑產生的異戊烯基焦磷酸和二甲基烯丙基焦磷酸合成[5]。在香葉基焦磷酸合酶的催化作用下，這些合成物縮合生成香葉基焦磷酸[6]，隨後在二磷酸龍腦合酶的作用下環化成二磷酸龍腦，最終在鹼性磷酸酶的作用下脫去磷酸基團生成龍腦[2]。此外，龍腦在龍腦脫氫酶的催化作用下被氧化成樟腦[7]。
冰片極易被氧化成酮而生成樟腦，人工合成方法是通過Meerwein–Ponndorf–Verley還原反應將樟腦還原成冰片。加入硼氫化鈉可以加快反應速率，使反應成為不可逆反應，這是由於動力學控制反應產物為異冰片。
冰片被認為具有抗菌、保護心腦血管、鎮痛消炎、防止血栓、促進藥物透過血腦屏障等多種作用[8]。常應用於臨床治療，作為止痛劑、鎮痛劑和麻醉劑[9]。
冰片具有劑量毒性，大量使用會引起毒性反應。[10]
Wang, Hong; Ma, Dongming; Yang, Jinfen; Deng, Ke; Li, Meng; Ji, Xiaoyu; Zhong, Liting; Zhao, Haiying. An Integrative Volatile Terpenoid Profiling and Transcriptomics Analysis for Gene Mining and Functional Characterization of AvBPPS and AvPS Involved in the Monoterpenoid Biosynthesis in Amomum villosum. Frontiers in Plant Science. 2018-06-20, 9. doi:10.3389/fpls.2018.00846. Chen, Changjie; Miao, Yuhuan; Luo, Dandan; Wang, Zixin; Guo, Lujuan; Zhao, Tingting; Liu, Dahui. Cloning and Functional Verification of the Borneol Dehydrogenase Encoding Gene AArBDH1 in Artemisia argyi. Chinese Bulletin of Botany. 2023-07-01, 58 (4): 560. doi:10.11983/CBB22123. Xingxing, Liu; Xi, Zhang; Xiali, Guo; Shangji, Gong; Xiangmei, Jiang; Yuxin, Fu; Liping, Luo. Multivariate Analyses of Volatile Chemical Composition in Leaves of Different Cinnamomum camphora Chemotypes. Chinese Bulletin of Botany. 2014, 49 (2): 161. doi:10.3724/SP.J.1259.2014.00161. Ho, Tsung-Jung; Hung, Chien-Che; Shih, Tzenge-Lien; Yiin, Lih-Ming; Chen, Hao-Ping. Investigation of borneols sold in Taiwan by chiral gas chromatography. Journal of Food and Drug Analysis. 2018-01, 26 (1): 348–352. doi:10.1016/j.jfda.2016.10.012. Hurd, Matthew C.; Kwon, Moonhyuk; Ro, Dae-Kyun. Functional identification of a Lippia dulcis bornyl diphosphate synthase that contains a duplicated, inhibitory arginine-rich motif. Biochemical and Biophysical Research Communications. 2017-08, 490 (3): 963–968. doi:10.1016/j.bbrc.2017.06.147. Ma, Rui; Su, Ping; Guo, Juan; Jin, Baolong; Ma, Qing; Zhang, Haiyan; Chen, Lingli; Mao, Liuying; Tian, Mei; Lai, Changjiangsheng; Tang, Jinfu; Cui, Guanghong; Huang, Luqi. Bornyl Diphosphate Synthase From Cinnamomum burmanni and Its Application for (+)-Borneol Biosynthesis in Yeast. Frontiers in Bioengineering and Biotechnology. 2021-02-11, 9. doi:10.3389/fbioe.2021.631863. Khine, Aye Aye; Lu, Pei-Chieh; Ko, Tzu-Ping; Huang, Kai-Fa; Chen, Hao-Ping. Cloning, expression, identification and characterization of borneol dehydrogenase isozymes in Pseudomonas sp. TCU-HL1. Protein Expression and Purification. 2020-11, 175: 105715. doi:10.1016/j.pep.2020.105715.
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