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The preserved fungal species Antrodia camphorata has diverse health-promoting effects and has been popularly used in East Asia as a traditional herb. We isolated a volatile compound from the culture medium of A. camphorata and identified it as gamma-dodecalactone (gamma-DDL). Cytomic screening for immune-modulating activity revealed that gamma-DDL can activate human NK cells to express the early activation marker CD69. Further experiments showed that gamma-DDL not only can induce NK cells to express CD69 but also stimulate NK cells to secrete cytotoxic molecules (FasL and granzyme B) and Th1 cytokines (TNF-alpha and INF-gamma). Measuring the distribution of gamma-DDL in the subcellular compartments of NK cells revealed that gamma-DDL has been converted to 4-hydroxydodecanoic acid (an acyclic isomer of gamma-DDL) in a time-dependent manner in the cytoplasm. Synthetic (R,S)-4-hydroxydodecanoic acid activated NK cells to express CD69 mRNA within 10min, in contrast to gamma-DDL, which activated NK cells to express CD69 within 50min. This faster activation suggests that gamma-DDL has converted to 4-hydroxydodecanoic acid and to stimulate the NK cells to express CD69. Optically pure (R)-(+)-4-hydroxydodecanoic acid and (S)-(-)-4-hydroxydodecanoic acid were obtained via: (1) synthesis of its diastereomeric esters of (R,S)-4-hydroxydodecanoic (R)-(-)-2-phenylpropionate; (2) separation of diastereomers via preparative HPLC, and (3) subsequent hydrolysis of the obtained optical pure ester of (R)-(+)-4-hydroxydodecanoic acid (R)-(-)-2-phenylpropionate and (R)-(-)-4-hydroxydodecanoic acid (R)-(-)-2-phenylpropionate, respectively. Further assays of NK cells activation using each enantiomer showed that only the (R)-(+)-4-hydroxydodecanoic acid can activate NK cells., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)