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New monocyclic monoterpenoid glycoside from Mentha haplocalyxBriq.
Chemistry Central Journalvolume 6, Article number: 37 (2012)
Two new monocyclic monoterpenoid glycosides,rel-(1R,2S,3R,4R) p-menthane-1,2,3-triol3-O-β-D-glucopyranoside (1) and rel-(1S,2R,3S) terpinolene-1,2,3-triol3-O-β-D-glucopyranoside (2) were isolated from aqueous acetone extract of theaerial parts of Mentha haplocalyx Briq.. Their structures were elucidated through spectralanalysis using MS and NMR spectrometers.
Mentha species are used for their flavoring and medicinal properties widely throughoutthe world . Mentha haplocalyx Briq., is widely used in food, cosmetics and medicines,distributed in the southwest of China . It has traditionally been used to treat various diseases of breath, procreation anddigestive systems in China. Primary investigation on this plant has led to the isolation ofpolyphenolic acids, several flavonoids and monoterpenoids [3–6], and in a continuation study to obtain minor constituents, two new monocyclicmonoterpenoid glycosides, rel- (1R,2S,3R,4R)p-menthane-1,2,3-triol 3-O β-D-glucopyranoside (1) andrel- (1S,2R,3S) terpinolene-1,2,3-triol3-O β-D-glucopyranoside (2) were obtained (Figure 1). This paper deals with the isolation and identification of these new compounds.
Repeated column chromatography (CC) of the chlorophyll removal fraction in the 70% aqueousacetone extract obtained from the aerial parts of M. haplocalyx over DianionHP 2MGL, MCI-gel CHP-20P and silica gel resulted in the isolation of twocompounds. On the basis of spectroscopic methods, including 2D-NMR (HMQC, HMBC,1H-1H COSY and NOESY), the structures of two new were determined asrel- (1R,2S,3R,4R) p-menthane-1,2,3-triol3-O-β-D-glucopyranoside (1) and rel-(1S,2R,3S) terpinolene-1,2,3-triol3-O-β-D-glucopyranoside (2).
Compound 1 was obtained as a pale amorphous powder. Its HR-ESI-MS displayed quasi-molecular-ionpeak [M + Na]+ at m/z 373.1521([C16H30O8Na]+), and the EI-MS gave fragment-ion peaksat m/z 171 [M + 1–162(glucosyl)-H2O]+and 153 [M + 1–162(glucosyl)-2H2O]+corresponding to a molecular formula C16H30O8, with thepresence of 16 carbon signals in the 13C-NMR spectrum.
The 1H- and 13C-NMR spectral data displayed the presence of two secondarymethyl δ 0.81 (3H, d J = 7.0 Hz, H-10), 0.92 (3H,d J = 7.0 Hz, H-9)], a tertiary methyl δ 1.21 (3H,s, H-7)], two methylenes δ 1.37 (2H,dt J = 11.7, 8.3 Hz, H-5), 1.40 (1H, m, H-6α) and 1.57 (1H,m, H-6β)], four methines (two of them was oxygenated) δ 3.82 (1H,d J = 10.8, 9.2 Hz, H-3), 3.33 (1H,d J = 10.8 Hz, H-2), 2.31 (1H, m, H-8), and 1.69 (1H, m, H-4)],and an oxygentated quaternary carbon, suggesting that compound 1 was a menthane-type monoterpenewith three OH-groups [7, 8]. Moreover, 1H-1H COSY correlations were observed betweenH-C(9)/H-C(8)/H-C(10), H-C(8)/H-C(4), and H-C(6)/H-C(5)/H-C(4)/H-C(3)/H-C(2), that the deduced spinsystem implied that the three OH-groups were located at C(1), C(2) and C(3) in 1, respectively. Inaddition, one glucopyranosyl unit δ (H) 4.33 (1H,d J = 8.2 Hz, H-(1′)), δ(C) 105.9(C-1′)] was evident from 1H- and 13C-NMR of 1. The J value(8.2 Hz) of the anomeric proton concluded the β-configuration of the glucosemoiety, suggesting that 1 was a p-menthane-1,2,3-triol glycoside. This was furtherconfirmed by the HMBC experiment, in which correlations of the glucosyl H-1′ (δ4.33) with the C(3) (δ 81.9) were observed. Furthermore, other HMBC correlationsconfirmed the structure of compound 1. Thus, these 2D-NMR methods deduced compound 1 asp-menthane-1,2,3-triol 2-O β-D- glucopyranoside. The couplingconstants of 10.8 Hz for H-C(3)/H-C(2), 9.2 Hz for H-C(3)/H-C(4) for 1 showed thatH-C(2), H-C(3) and H-C(4) were axial protons. The relative configuration at C(1) was determined fromROESY correlation of δ 1.21 (Me(7)) with H-2 (δ 3.33). It was in goodagreement with those of rel-(1R,2S,3R,4R,6S)p-menthane-1,2,3,6-tetrol . Therefore 1 should possessrel-(1R,2S,3R,4R)-configuration.
Compound 2 was obtained as a white amorphous powder. Its molecular formula was assigned asC16H28O8 on the basis of the 13C-NMR data and negativeHR-ESI-MS (m/z 347.1711 [M-H]-), which was 2 amu less than that of 1.
The 1H- and 13C-NMR spectra of compounds 1 and 2 were very similar and gavesame signals assignable to two secondary methyl, a tertiary methyl, two methylenes, two oxygenatedmethines, an oxygenated quaternary carbon and a β-D-glucopyranosyl unit. Comparison ofthe NMR data of 2 and 1 indicated that the only difference was the presence of two olefinic carbonsin 2 instead of the two methines in 1. It suggested that a double bond situated at C(4) and C(8)positions in 2. This was supported by the IR spectrum showing a strong band at1649 cm-1, probably due to a tetra-substituted double bond and the correlations ofthe H-C(5) with the olefinic carbons C-4 and C-8 observed in the HMBC spectrum. The1H-1H COSY interactions of H-2 (δ 3.37)/H-3 (δ5.02), and H-5 (δ 2.42, 2.14)/H-6 (δ 1.75, 1.33) provided C-2 and C-3positions. This was sustained by the HMBC experiment showing correlations of H-3 (δ5.02) with the C(1), C(2), C(4), C(5) and C(8) observed, respectively. It reveals aterpinolene-1,2,3-triol fragment in 2 . The full assignments of the aglycon and sugar signals were carried out by HSQC,1H-1H COSY and HMBC experiments. The HMBC correlations of glucosyl H-1′(δ 4.09) in 2 with the C(3) at δ 76.1 confirmed the location of glucosylat C(2). The coupling patterns [(δ 3.37,d J23 = 2.86, H-2) and (δ 5.02,d J2, 3 = 2.86, H-3)] demonstrated that H-C(2) and H-C(3)were axial-equatorial or equatorial-equatorial couplings. In the ROESY experiments that H-2 and Me-7ROESY correlation was missing, while H-3 and Me-7 was present. It was illustrated that H-2 and H-3trans located on the alpha and beta face, respectively. Therefore, the structure of 2 wasdetermined to be rel- (1S, 2R, 3S) terpinolene-1,2,3-triol3-O β-D- glucopyranoside .
Optical rotations were measured on a P-1020 Polarimeter (JASCO, Tokyo, Japan). IR spectra:IR-450 spectrometer with KBr pellets; 1H- and 13C-NMR, HSQC, HMBC and1H-1H COSY, ROESY spectra: DRX-500 spectrometers operating at500 MHz for 1H, and 125 MHz for 13C, respectively, inCD3OD; ESI-MS, EI-MS and HR-EI-MS: APEX II FT-ICR and VG-ZAB-HS spectrometer.Column chromatography (CC): Dianion HP 2MGL, Silica gel, and MCI-gel CHP 20P. TLC:silica gel G plates with CHCl3-MeOH-H2O (8:2:0.2 or 7:3:0.5).
The aerial parts of M. haplocalyx was purchased from Beijing TongRenTangMedicinal Material Co., Beijing, China, in June 2006, and identified by Prof. B.L., in Beijing University of Chinese Medicine.
Extraction and isolation
The aerial parts of M. haplocalyx (5.0 kg) was extracted with 70% aqueousacetone three times (10 L × 3) at room temperature. After removal of theorganic solvent under reduced pressure, the aqueous solution was partitioned with ethyl ether toyield ethyl ether and aqueous fraction. The aqueous fraction was concentrated to a small volume(200 ml) and subjected to a Dianion HP 2MGL column, eluting with H2O-MeOH(1:0–0:1) to afford six fractions (Frs. 1–6). Frs. 4 (4 g) wassubjected to CC on silica gel (CHCl3/MeOH, 9:1–7:3) and MCI-gel CHP20Peluted with H2O/MeOH to give 1 (3 mg) and 2 (4 mg).
(1R,2S,3R,4R) p-menthane-1,2,3-triol3-O-β-D- glucopyranoside (1): pale amorphous powder,[α] = +5.1° (c = 0.187, MeOH), IR(KBr): 3363, 2919, 1372, 1259, 1162, 1034. 1H-NMR (CD3OD, 500 MHz) and13C-NMR (CD3OD, 125 MHz): Table 1 showed. EI-MSm/z 171 [M + 1 − 162(glucosyl)-H2O]+ and 153 [M + 1 − 162(glucosyl)-2H2O]+, 135, 127, 112, 97, 84, 73, 55. HR-ESI-MS: m/z 373.1521([C16H30O8Na]+), calcd forC16H30O8Na, 373.1990.
(1S,2R,3R) terpinolene −1,2,3-triol3-O-β-D- glucopyranoside (2): pale amorphous powder,[α]= –44.9° (c = 0.323, MeOH), IR(KBr): 3308, 2938, 1649, 1449, 1341, 1259, 1076. 1H-NMR (CD3OD, 500 MHz)and 13C-NMR (CD3OD, 125 MHz): Table 1 showed.ESI-MS: m/z 347.2 [M-H]-, 185.1[M-H-162(glucosyl)]-. HR-ESI-MS: m/z 347.1711[M-H]-, calcd for C16H27O8, 347.1710.
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This work was supported by the Research Fund for the Doctoral Program of Higher Education ofChina (No. 20100013110002), the National Natural Science Foundation of China (No. 81173520), theResearch Fund for Self-selected Topic of Beijing University of Chinese Medicine (No. 0100600122) andBeijing Nova Program (No. 2011070).
The authors declare that they have no competing interests.
GS carried out the chemical analysis-structure elucidation and drafted the Manuscript; CX carriedout the chemical and biological studies; BL conceived of the study and its design and coordinationof the scientific teams. All authors have read and approved the final manuscript.
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