Chemical Constituents from Berchemia polyphylla var. Leioclada (2024)

Associated Data

Supplementary Materials

Abstract

Introduction

The genus Berchemia,belonging to the family Rhamnaceae,consists of 31 species worldwide. These species are primarily foundin temperate and tropical regions across east to southeast Asia. Approximately18 species are distributed in the southern part of China. Medicinally,the roots, stems, or leaves of some Berchemia speciesare utilized for their ability to dispel wind and dampness, promoteblood circulation, relieve pain, and alleviate cough and phlegm. Naturalproducts derived from Berchemia plants include flavonoids,glycosides, lignans, quinones, and terpenes. Notably, dimeric quinonesextracted from this genus exhibit significant biological activity,highlighting their distinctive role as key components.¹ “Tiebaojin” is a frequently used traditionalmedicine in Guangxi Zhuang and southwest minority areas of China.After conducting investigations, it has been found that “Tiebaojin”is derived from four species of the Berchemia genus,namely, Berchemia lineata, Berchemia floribunda, Berchemia polyphylla Wall. ex Laws., and B. polyphylla var. leioclada. According to the “Guangxi Standards of ChineseMedicinal Materials” and the “Dictionary of TraditionalChinese Medicine”, B. lineata has been identified as the primary plant source of “Tiebaojin”.^2,3 Due to the extensive use of B. lineata in Zhuang medicine compound preparations, its resources are depletingrapidly. Therefore, it is imperative to intensify research effortson the other three plant sources of “Tiebaojin”.⁴

Previous studies have focused on phytochemicalinvestigations ofthe stems and leaves of B. lineata,which have identified several new phenolic compounds including naphthopyrones,flavonoids, and bibenzyls.⁵ However, thereis limited research on the chemical constituents of B. polyphylla var. leioclada, which is another sourceof “Tiebaojin”.⁶ This studyaims to compare the chemical components of B. lineata and B. polyphylla var. leiocladato provide a scientific basis for the use of the latter as “Tiebaojin”and to expand the medicinal plant resources associated with it. Inthis study, we have identified and characterized three new dimericquinones named berpolydiquinones A-C (1–3) and one new dimeric naphthalene named berpolydinaphthaleneA (4). Additionally, we have isolated 21 known phenoliccompounds (8–25) with diverse carbonskeletons from the stems and leaves of B. polyphylla var. leioclada. The isolation and structural elucidation of thesepreviously undescribed dimeric quinones and naphthalene are presentedin this article (Figure ​Figure11).

Results and Discussion

Compound 1 was obtained as a yellow, amorphous powder.The molecular formula was assigned as C₃₀H₂₆O₁₀ based on high-resolution electrospray ionization massspectroscopy (HR-ESI-MS) (m/z 547.16008[M + H]⁺, calcd for C₃₀H₂₇O₁₀, 547.15987). The ¹H NMR spectrum (Table 1) of compound 1 showed the presenceof various groups, including two methoxy groups at δ_H 3.89 (3H, s, 2-OCH₃) and 3.87 (3H, s, 2′-OCH₃), four methyl groups at δ_H 1.62 (3H, d, J = 6.6 Hz, CH₃-12′), 1.26 (3H, d, J = 6.0 Hz, CH₃-11′), 2.57 (3H, s, CH₃-12), and 2.38 (3H, s, CH₃-13). Additionally, therewas a double-bonded proton at δ_H 6.26 (1H, s, H-3′),an isolated aromatic proton at δ_H 7.58 (1H, s, H-8),two oxymethines at δ_H 3.67 (1H, m, H-7′) and5.13 (1H, q, J = 6.6 Hz, H-5′), and a methylenegroup at δ_H 2.61 (1H, m, H_a-8′),2.28 (1H, m, H_b-8′). The ¹³C NMR, DEPT,and HSQC spectra confirmed the presence of 30 carbons, including 4CH₃ groups, 2 OMe groups, 2 sp² CH groups, 1sp³ CH₂ group, 2 sp³ CH groups, and5 conjugated carbonyl groups at δ_C 181.6 (C-1′),192.9 (C-4′), 181.6 (C-1), 191.1 (C-4), 205.1(C-11). In addition,there are 14 sp² nonprotonated carbons. A comparison ofthe NMR data of compound 1 with those of floribundiquinonesA-C revealed that these compounds contained the same benzisochromanquinonemoiety, which was identified the subunit as 7-dehydroxyventiloquinoneH with an additional quaternary carbon at C-9′.^7,8 Apart from the signals of the 7-dehydroxyventiloquinone H moiety,the remaining signals included one methyl group [δ_H 2.38 (3H, s, H-13), δ_C 20.2 (q)], one methoxy group[δ_H 3.89 (3H, s), δ_C 61.6 (q)],one acetyl group [δ_H 2.57 (3H, s, H-12), δ_C 32.1 (q), 205.1 (s)], one sp² methine [δ_H 7.58 (1H, s, H-8), δ_C 122.4 (d)], two conjugatedcarbonyls [δ_C 181.6 (s), 191.1 (s)] and seven sp² nonprotonated carbons. The additional NMR data indicatedthe presence of a naphthoquinone unit with a methoxy, a methyl, anacetyl, and a hydroxyl group. By comparing the remaining NMR datawith the literature on 2-methoxystypandron,^9,10 itwas observed that the quinone ring did not have a double-bonded protonand had an extra nonprotonated carbon. These findings suggested thatthe substituent pattern of the benzene ring in the naphthoquinoneunit was consistent with that of 2-methoxystypandron, which was furtherconfirmed by HMBC correlations (Figure ​Figure22). Due to the lack of relevant ROESY correlations,the methoxy group can be attached to either C-2 or C-3 on the quinonering, allowing for a nonbiaryl connectivity between the two unitsthrough C-9′ to C-2 or C-9′ to C-3. Through ROESY correlationof H-5′ and H-7′, it was determined that they are inthe cis orientation, consistent with the literaturereports on floribundiquinones A–D. This suggests that the benzisochromanquinonesisolated from Rhamnaceae plants exhibit the same chirality from abiogenetic perspective. Additionally, we successfully isolated 7-dehydroxyventiloquinoneH and confirmed its absolute configuration through equivalent circulatingdensity (ECD) calculations, which aligns with the biosynthetic analysis.Thus, the absolute configurations of C-5′ and C-7′ weredetermined as R and S, respectively.⁷

Although compound (1) consisted of two structurallyand electronically different electronic transition dipole moments(TDMs), the exciton chirality method (ECM) was still applicable todetermine the absolute configuration of the nonbiaryl axis. Accordingto the ECM rule, the coupling of the transition dipole moments (TDMs)resulted in a negative first cotton effect (CE) at longer wavelengthsand a positive second CE at shorter wavelengths, indicating a negativechirality. Conversely, a positive first CE and a negative second CEindicated a positive chirality. The positive chirality suggests thatthe TDMs of the two chromophores are oriented in a clockwise manner,while the negative chirality suggests that the TDMs of the two chromophoresare oriented in an anticlockwise manner.^11,12 In the ECD spectrum of compound 1, a negative CE isobserved around 307 nm, while a positive CE is observed around 286nm. These CE values indicate the presence of negative chirality, whichcan be attributed to the anticlockwise arrangement of the two naphthoquinonechromophores. Taking into account the position of the nonbiaryl axis,compound 1 could potentially have two diastereomers (P)-3, 9′-linkage 1a and (M)-2, 9′-linkage 1b. To confirm the structureof compound 1, we conducted NMR calculations with DP4+analysis on two possible diastereomers: [(P)-3, 9′-linkage]-1a and [(M)-2, 9′-linkage]-1b.^13,14 The DP4+ analysis showed that[(P)-3, 9′-linkage ]-1a, witha 100% DP4+ probability, was the most likely structure for compound 1 (Figure ​Figure33). As a result, the structure of compound 1 was determinedand was named berpolydiquinone A.

Compound 2 was obtainedas a yellow amorphous powder.The molecular formula was determined to be C₂₉H₂₀O₉ based on HR-ESI-MS (m/z 513.11841 [M + H]⁺, calcd for C₂₉H₂₁O₉, 513.11801). A comparison of the NMR data of compound 2 with those of 2-methoxystypandron and chrysophanol indicatedthat compound 2 is a naphthoquinone-anthraquinone dimerconsisting of two subunits: 2-methoxystypandron and chrysophanol.^10,15 When compared to the NMR data of floribundiquinone E,¹⁶ compound 2 lacks the signal ofa methoxy group and an isolated aromatic proton but exhibits a pairof ortho-coupled aromatic proton signals at δ_H 7.92 (1H, d, J = 7.8 Hz) and 7.33 (1H, d, J = 7.8 Hz), indicating that the two subunits are connectedthrough C-8 to C-7′. HMBC correlations from H-6′ to130.7 (s, C-8), H-5′ to 135.8 (s, C-7′) and from CH₃-13 to 130.7 (s, C-8) confirmed this deduction. The ECD spectrumof compound 2 exhibited a negative chirality, indicatingthat the two chromospheres in space rotated in an anticlockwise manner.This observation establishes the axial chirality as the absolute M-configuration.¹⁷ Based on thesefindings, the structure of compound 2 was determinedand named berpolydiquinone B.

Compound 3 was obtainedas a yellow, amorphous powder.The molecular formula was determined to be C₂₈H₂₀O₉ based on HR-ESI-MS (m/z 501.11768 [M + H]⁺, calcd for C₂₈H₂₁O₉, 501.11801). A comparison of the NMR data of compound 3 with those of 3-methoxy-7-methyljuglone and physcion revealedthat compound 3 is a naphthoquinone-anthraquinone dimercomposed of two subunits: 3-methoxy-7-methyijuglone and physcion.^18,19 When comparing the NMR data of 3-methoxy-7-methyljuglone and physcionwith compound 3, it was observed that compound 3 lacks two pairs of meta-coupled aromaticproton signals but exhibits two isolated aromatic protons at δ_H 7.68 (1H, s) and 6.84 (1H, s). In the HMBC spectrum, the5-OH signal at δ_H 12.38 (1H, s) showed correlationswith δ_C 112.2 (s, C-10), 158.9 (s, C-5), and 133.7(s), and the CH₃-13 signal at δ_H 2.07(3H, s) showed correlations with δ_C 121.7 (d, C-8),144.9 (s, C-7), and 133.7 (s). These correlations suggested that thechemical shift at δ_C 133.7 (s) corresponded to C-6.In the same way, the chemical shift at δ_C 120.3 (s)was assigned to C-5′. This assignment was supported by theHMBC spectrum. These findings indicate that the biaryl connectivityof two subunits is determined at the C-6 and C-5′ positions.The ECD spectrum of compound 3 also showed a negativechirality, suggesting the axial chirality as the absolute M-configuration.¹⁷ Based on thesefindings, the structure of compound 3 was determinedand named berpolydiquinone C.

Compound 4 was obtainedas a brown powder. The molecularformula was determined to be C₃₂H₃₄O₈ based on HR-ESI-MS (m/z 569.21399[M + Na]⁺, calcd for C₃₂H₃₄O₈Na, 569.21459). The ¹³C and DEPT NMR spectra (Table 2) displayed 16 carbonsignals, including three sp² methines, seven sp² quaternary carbons, one methoxy group, two methyl groups, and threeoxygenated sp³ methines. Based on the HR-ESI-MS data, itcan be deduced that compound 4 is a derivative of dimericnaphthalene with a symmetrical structure. The ¹H–¹H COSY correlations of H-2/H-3/H-4; HMBC correlations fromH-2 to δ_C 158.5 (s, C-1), 116.5 (s, C-9); as wellas MeO to δ_C 158.5 (s, C-1) suggested that compound 4 contained a 1,2,3-trisubstituted benzene ring with a methoxygroup at the C-1 position. Based on the ¹H–¹H COSY and HSQC experiments, it can be deduced that thereare two structural fragments: a CH₃(CH)O– and b−CH(O)CH(O)CH₃. The HMBC correlations from H-11to δ_C 81.7 (d, C-14) indicate that these two fragmentsare connected through an ether bond at the C-11 and C-14 positions,resulting in the formation of a 1-methyl-2-(2-hydroxy-propyl)-dihydrofuranring. Furthermore, the HMBC correlations from H-14 to δ_C 149.8 (s, C-8), 127.2 (s, C-7), and 141.6 (s, C-6), alongwith the correlations from H-11 to δ_C 120.6 (s, C-5)and 141.6 (s, C-6), suggest that the C-8 position of the naphthalenering is substituted by a hydroxyl group and that the furan ring isfused to the C-6 and C-7 positions of the naphthalene ring. The biarylconnectivity at the C-5 positions was determined based on the factthat C-5 is a quaternary carbon and its chemical shift is downfield.Compound 4 was identified as a dimer of naphthofuran,formed by the polymerization of two identical monomers at the C-5-C-5′position through a σ bond. The relative configuration of compound 4 was deduced by using the ROESY spectrum and DP4+ analysis.The cis orientation between H-11 and H-14 was determinedbased on the ROESY correlations of H-14 (δ_H 5.70)/H-11(δ_H 4.85). As the biaryl axis and the configurationof C-12 have not been determined, compound 4 may havefour diastereoisomers, including [(M)-11R*, 12S*, 14R*, 11′R*, 12′S*, 14′R*]-4a, [(M)-11R*,12R*, 14R*, 11′R*, 12′R*, 14′R*]-4b, [(M)-11S*, 12S*, 14S*, 11′S*,12′S*, 14′S*]-4c, and [(M)-11S*, 12R*, 14S*, 11′S*,12′R*, 14′S*]-4d. To verify the relative configuration of compound 4, NMR calculations were performed with DP4+ analysis on thefour possible isomers. According to DP4+ analysis, it was determinedwith a 100% probability that the structure of compound 4 is [(M)-11R*, 12R*, 14R*, 11′R*, 12′R*, 14′R*]-4b (Figure ​Figure44). Compound 4 is classified as a member of 1,1′-binaphthyl. TheECM rule can also be used to determine the absolute configurationof the biaryl axis. In the ECD spectrum of compound 4, a negative CE at 244 nm and a positive CE at 226 nm were observed,indicating a negative chirality. The absolute M-configurationwas assigned to the biaryl axis.²⁰ Therefore,the compound was determined and named berpolydinaphthalene A.

Additionally, the remaining phenolic compoundswere identifiedas floribundiquinone E (5),¹⁶ quercetin (6),²¹ kaempferol(7),²² tricin (8),²³ isorhamnetin (9),²⁴ 5,7,4′-trihydroxy-3,3′,5′-trimethoxyflavone(10),²⁵ naringenin (11),²⁶ 5,7,3′,4′-tetrahydroxy-2-methoxy-3,4-flavandione-3-hydrate(12),²⁷ 2,5-dimethyl-7-hydroxychromone(13),²⁸ 2,5-dimethyl-7-methoxychromone(14),²⁹ vittarin-B (15),³⁰ 3-methoxy-5-[2-(4-methoxyphenyl)ethyl]phenol(16),³¹ (11S)-diaprothin (17),³² citreoisocoumarinol(18),³³ eleutherol (19),³⁴ bercheminol C (20),⁵ rubrofusarin-6-O-α-l-rhamnosyl-(1 → 6)-O-β-d-glucopyranoside (21),³⁵ bercheminolA (22),⁵ chrysophanol (23),³⁶ emodin (24),³⁷ and glucofrangulin A (25)³⁸ by comparisons of their spectroscopic data withreported values.

In this study, 25 phenolic compounds were isolatedand identifiedfrom the stems and leaves of B. polyphylla var. leioclada. These compounds can be categorized into four dimericquinone (1–3, 5), twonaphthalenes (4, 19), seven flavonoids (6–12), two chromones (13–14), two bibenzyls (15–16), two isocoumarins (17–18), twonaphthopyrones (20–21), a phenoliccompound with a novel carbon skeleton (22), and threeanthraquinones (23–25). Notably,compounds 4, 17–19 havenot been previously found in the family Rhamnaceae. Compound (4) is particularly interesting as it is a new structure typeof dimeric naphthalene with a symmetrical structure. Flavonoids, alarge class of polyphenols, were also found in the genus Berchemia plant. In this work, seven flavonoids (6–12) were isolated from B. polyphylla var. leioclada. Among them, compounds 6–7 and 9–10 were flavonols,compound 8 was a flavone, compound 11 wasa dihydroflavone, and compound 12 was a hydrate of flavonoids.Flavonoids are considered to be the traditional active ingredientsof the genus Berchemia plant, with quercetin beinga representative compound used for quality control of “Tiebaojin”due to its wide range of biological activities. In addition, quercetinwas isolated from two species of the genus Berchemia plant (B. polyphylla var. leiocladaand B. lineata), both of which areused as “Tiebaojin” in Zhuang medicine. Furthermore,compounds 7, 11, 13, 15, 20–22, and 24 were also isolated from B. polyphylla var. leioclada and B. lineata. Thesefindings provide a scientific basis for considering B. polyphylla var. leioclada as a source of “Tiebaojin”and expand the range of medicinal plants for the traditional medicine“Tiebaojin”. Dimeric quinones are distinctive chemicalconstituents found in plants belonging to the genus Berchemia. In this study, we have identified one novel naphthoquinone-benzisochromanquinonedimer, as well as two new naphthoquinone-anthraquinone dimers. Thesediscoveries contribute to the existing repertoire of quinone compoundsfound in this particular genus of plants. Consequently, our findingshighlight the significance of B. polyphylla var. leioclada as a valuable source of diverse phenolic compounds,warranting further investigation.

Experimental Section

Acknowledgments

This workwas supported by the National Natural Science Foundationof China (no. 81960762) and the National Key Research and DevelopmentProgram (no. 2022YFC3502200).

Supporting Information Available

The Supporting Informationis available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.3c08357.

• HRESIMS, UV, CD, and 1Dand 2D NMR spectra of compounds 1–4; NMR calculations of compounds 1 and 4 (PDF)

Author Contributions

^∥ W.-L.X. and Z.-Y.L. contributed equally to this work.

Notes

The authorsdeclare no competing financial interest.

Supplementary Material

References