Four New Phloroglucinol-Terpene Adducts from the Leaves of Myrciaria cauliflora
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ORIGINAL ARTICLE
Four New Phloroglucinol‑Terpene Adducts from the Leaves of Myrciaria cauliflora Ming Chen1,2 · Jia‑Qing Cao1 · Wen‑Jing Wang1,2 · Ni‑Ping Li1,2 · Yan Wu1,2 · Lei Wang1,2 · Wen‑Cai Ye1,2 Received: 25 September 2020 / Accepted: 13 November 2020 © The Author(s) 2020
Abstract Myrcauones A–D (1–4), four new phloroglucinol–terpene adducts were isolated from the leaves of Myrciaria cauliflora. Their structures with absolute configurations were elucidated by combination of spectroscopic analysis, single crystal X-ray diffraction, and electronic circular dichroism (ECD) calculations. Compound 1 was a rearranged isobutylphloroglucinol– pinene adduct featuring an unusual 2,3,4,4a,10,11-hexahydro-1H-3,11a-methanodibenzo[b,f]oxepin backbone. Compound 4 showed moderate antibacterial activity against Gram-positive bacteria including multiresistant strains. Graphic Abstract
Keywords Myrciaria cauliflora · Phloroglucinol–terpene adducts · Antibacterial activity
Ming Chen and Jia-Qing Cao contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13659-020-00288-4) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article
1 Introduction The plant Myrciaria cauliflora is an evergreen shrub and widely distributed in southern and central Brazil [1]. This plant has been traditionally used as a folk medicine to treat asthma, diarrhea, and gastrointestinal diseases [2, 3].
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Previous phytochemical investigations on this plant only reported essential oils and flavonoids [4–6]. As a part of our efforts to search for structural unique and bioactive constituents from Myrtaceae plants [7–10], four new phloroglucinol–terpene adducts, myrcauones A–D (1–4), were isolated from the leaves of M. cauliflora. Their structures and absolute configurations were determined by means of 1D and 2D NMR spectroscopy, X-ray diffraction analysis, and electronic circular dichroism (ECD) calculations. Compound 1 is a rearranged isobutylphloroglucinol–pinene adduct featuring an unusual 2,3,4,4a,10,11-hexahydro-1H-3,11amethanodibenzo[b,f]oxepin backbone. All isolates were evaluated for their antibacterial activities. Herein, we describe the isolation, structural elucidation, and antibacterial activities of these myrcauones A–D (1–4).
2 Results and Discussion 2.1 Structural Elucidation Compound 1 was obtained as yellow gum. The molecular formula of 1 was established as C22H32O3 by its HRESIMS data (m/z 345.2423 [M+H]+, calcd for C22H33O3: 345.2424). The UV spectrum displayed absorption maximum at 206 nm. The IR spectrum showed characteristic absorptions for hydroxyl group (3475 cm−1) and aromatic ring (1611 and
Fig. 1 Chemical structures of 1–4
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1488 cm−1). The 1H NMR spectrum of 1 suggested the presence of an olefinic proton [δH 6.23 (1H, s, H-5′)], a hydroxyl group [δH 4.75 (1H, s, 2′-OH)], a methoxy group [δH 3.76 (3H, s, H 3-11
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