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Molecules 2018, 23(11), 3003; https://doi.org/10.3390/molecules23113003

Natalenamides A–C, Cyclic Tripeptides from the Termite-Associated Actinomadura sp. RB99

1
School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
2
Leibniz Institute for Natural Product Research and Infection Biology—Hans-Knöll-Institute, Beutenbergstraße 11a, 07745 Jena, Germany
3
College of Bio-Nano Technology, Gachon University, Seongnam 13120, Korea
4
College of Korean Medicine, Gachon University, Seongnam 13120, Korea
5
College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Gwanak-gu, Seoul 08826, Korea
6
Forestry and Agriculture Biotechnology Institute, University of Pretoria, Pretoria 0028, South Africa
7
SKKU—Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 16419, Korea
*
Author to whom correspondence should be addressed.
Received: 1 October 2018 / Revised: 11 November 2018 / Accepted: 12 November 2018 / Published: 16 November 2018
(This article belongs to the Section Natural Products Chemistry)
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Abstract

In 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 13). 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 (13) 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. View Full-Text
Keywords: fungus-growing termite; Actinomadura sp.; tripeptides; natalenamides A–C; skin-whitening effects fungus-growing termite; Actinomadura sp.; tripeptides; natalenamides A–C; skin-whitening effects
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Lee, S.R.; Lee, D.; Yu, J.S.; Benndorf, R.; Lee, S.; Lee, D.-S.; Huh, J.; de Beer, Z.W.; Kim, Y.H.; Beemelmanns, C.; Kang, K.S.; Kim, K.H. Natalenamides A–C, Cyclic Tripeptides from the Termite-Associated Actinomadura sp. RB99. Molecules 2018, 23, 3003.

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