Isolation and biomimetic total synthesis of tomentodiones A–B, terpenoid-conjugated phloroglucinols from the leaves of Rhodomyrtus tomentosa

Abstract

Tomentodiones A (1) and B (2), a pair of C-11′ epimers of caryophyllene-conjugated phloroglucinols with an unprecedented skeleton, were isolated from the leaves of Rhodomyrtus tomentosa.

Tomentodione E, a new sec-pentyl syncarpic acid-based meroterpenoid from the leaves of Rhodomyrtus tomentosa

“…The NOE correlations between H-9 and H 3 -12 as well as H-1 and H 3 -13/H-5 indicated that the cyclobutane ring was trans-fused with the nine-member ring. Additionally, the relative configuration of the sesquiterpoid moiety of 1 (1a) could be further corroborated by comparison of the NMR data with the known meroterpenoids 2 and 3 [11,14,16]. Moreover, cross peaks between H 3 -14 and H-8′/H-6, between H-5 and H-7′ indicated that the sesquiterpenoid moiety was trans-fused with the dihydropyran ring ( Figure 3).…”

“…The four known compounds were identified as myrtucommulone K (2) [16], tomentodione B (3) [11], tomentodione C (4) [14] and tomentosenol A (5) [13], respectively, by comparison of their spectral data with those reported in the literatures.…”

“…Comparison of the NMR data assigned to 1a with those of myrtucommulone K (2), an XRD-confirmed meroterpenoid discovered from Myrtus communis [16], the similar NMR data confirmed the assignment of β-caryophyllene moiety. Moreover, the remaining 15 resonances in 13 C NMR data of 1 were assigned to a sec-pentyl syncarpic acid motif (1b) by detailed analyses of 1 H-1 H COSY and HMBC spectra of 1 ( Figure 2) as well as comparison with the known compound tomentodione B (3) [11,14]. The HMBC correlations between H-7′ and C-1′/C-5′/C-4/C-6/C-9′/C-11′ revealed that 1a and 1b were connected through the C-5-C-7′ bond ( Figure 2).…”

“…In China, the roots, stems, leaves, flowers, and fruits of R. tomentosa have been historically used as folk medicine and functional ingredients for a long time [2][3][4][5]. Previously phytochemical investigation revealed that phenols and terpenes were the major chemical constituents of R. tomentosa, which had been regarded as the key active components of this plant [6][7][8][9][10] leptospermone-based meroterpenoids with diverse skeletal types had been reported from the leaves of titled plant, some of which exhibited potential antibacterial and antitumor activities [11][12][13][14][15]. Structurally, it is assumed that these meroterpenoids arise from the crucial phloroglucinol precursor leptospermone coupled with mono-or sesquiterpenoid precursors through various conjugation manners to form diverse carbon skeletons.…”

Antioxidant activity and cytotoxicity property of extracts from various coastal plants against HepG2 cell lines

“…It is recommended that more detailed study such as deep and systematic phytochemical investigation and its mechanism of toxicity action to be carried out on the extracts of this study to figure out what caused the difference in cytotoxicity displayed by the leaves and root extract of the plant. In recent years, there are considerable phytochemical studies aimed at exploring the relatively unknown R. tomentosa leaves and have resulted in the isolation of several unique phloroglucinols which are all novel to science (Hiranrat and Mahabusarakam, 2008;Liu et al, 2016). However, their cytotoxicity is yet to be tested and more can be done in the future to determine their bioactivities.…”