Lee, Seoung RakLee, DahaeYu, Jae SikBenndorf, RenéLee, SullimLee, Dong-SooHuh, JungmooDe Beer, Z. WilhelmKim, Yong HoBeemelmanns, ChristineKang, Ki SungKim, Ki Hyun2019-10-082019-10-082018-11Lee, S.R., Lee, D.2., Yu, J.S., et al. 2018, 'Natalenamides A⁻C, Cyclic tripeptides from the termite-associated actinomadura sp. RB99', Molecules, vol. 23, no. 11, art. 3003, pp. 1-12.1420-3049 (print)1420-3049 (online)10.3390/molecules23113003http://hdl.handle.net/2263/71616In recent years, investigations into the biochemistry of insect-associated bacteria have increased. When combined with analytical dereplication processes, these studies provide a powerful strategy to identify structurally and/or biologically novel compounds. Non-ribosomally synthesized cyclic peptides have a broad bioactivity spectrum with high medicinal potential. Here, we report the discovery of three new cyclic tripeptides: natalenamides A⁻C (compounds 1⁻3). These compounds were identified from the culture broth of the fungus-growing termite-associated Actinomadura sp. RB99 using a liquid chromatography (LC)/ultraviolet (UV)/mass spectrometry (MS)-based dereplication method. Chemical structures of the new compounds (1⁻3) were established by analysis of comprehensive spectroscopic methods, including one-dimensional (¹H and 13C) and two-dimensional (¹H-¹H-COSY, HSQC, HMBC) nuclear magnetic resonance spectroscopy (NMR), together with high-resolution electrospray ionization mass spectrometry (HR-ESIMS) data. The absolute configurations of the new compounds were elucidated using Marfey's analysis. Through several bioactivity tests for the tripeptides, we found that compound 3 exhibited significant inhibitory effects on 3-isobutyl-1-methylxanthine (IBMX)-induced melanin production. The effect of compound 3 was similar to that of kojic acid, a compound extensively used as a cosmetic material with a skin-whitening effect.en© 2018 by The Authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/).Actinomadura spFungus-growing termiteNatalenamides A–CSkin-whitening effectsTripeptidesArticle