J. Park et al.
Phytochemistry 187 (2021) 112782
d, J = 14.3 Hz, H-8′′)/113.9 (C-8′′) and 5.03 (2H, d, J = 16.2 Hz,
H-10′′)/116.9 (C-10′′)), two methylenes (2.43 (2H, dd, J = 7.3 and 14.5
Hz, H-4′′)/28.4 (C-4′′) and 2.37 (2H, dd, J = 6.8 and 7.9 Hz, H-5′′)/31.1
(C-5′′)), and one methyl (1.84 (3H, s, H-9′′)/12.6 (C-9′′)). The 13C NMR
signals at δC 169.4 (C-1′′), 146.8 (C-6′′), and 128.9 (C-2′′) suggested the
presence of one carboxylic and two olefinic quaternary carbons,
respectively. The COSY NMR data showed correlations between
H-3′′/H-4′′, H-4′′/H-5′′ and H-7′′/H-8′′, and the HMBC correlations from
H-3′′ to C-1′′ and C-9′′, H-4′′ to C-2′′, C-3′′, and C-6′′, H-5′′ to C-3′′, C-6′′,
C-7′′, and C-10′′, H-7′′ to C-5′′, C-6′′, and C-10′′, H-8′′ to C-6′′ and C-7′′,
H-9′′ to C-1′′, C-2′′, and C-3′′, and H-10′′ to C-5′′ and C-7′′ suggested the
presence of 2-methyl-6-methylene-2,7-octadienoate. Finally, the struc-
ture of compound 1 was completed based on the HMBC correlation
between H-6 of the β-arbutin moiety and C-1′′ of the 2-methyl-6-methy-
lene-2,7-octadienoyl group. Consequently, the structure of compound 1
was identified as 6-O-(2-methyl-6-methylene-2,7-octadienoyl)-arbutin.
Compound 2 was obtained as a white powder, and its molecular
formula was determined to be C22H30O9 by HRESIMS analysis (m/z
437.1834 [M-H]- calcd for 437.1812). The 1D and 2D NMR data of 2
showed similar patterns to those of 1, except for the signals of the linear
monoterpenoid moiety that was attached to C-6 of the glucopyranosyl
group. The 1D and HSQC NMR data showed the presence of two olefinic
groups (δH/δC 6.79 (1H, td, J = 1.4 and 7.3 Hz, H-3′′)/143.7 (C-3′′) and
5.39 (1H, t, J = 6.1 Hz, H-7′′)/125.7 (C-7′′)), one oxymethylene (4.08
(2H, d, J = 6.7 Hz, H-8′′)/59.4 (C-8′′)), two methylenes (2.36 (2H, dd, J
= 7.4 and 14.9 Hz, H-4′′)/28.0 (C-4′′) and 2.16 (2H, t, J = 7.6 and 7.6 Hz,
H-5′′)/39.1 (C-5′′)), and two methyl groups (1.85 (3H, s, H-9′′)/12.5 (C-
9′′) and 1.70 (3H, s, H-10′′)/16.2 (C-10′′)). The 13C NMR signals at δ
C
169.4 (C-1′′), 138.5 (C-6′′), and 128.9 (C-2′′) indicated the presence of
one carboxylic and two olefinic quaternary carbons, respectively. The
COSY NMR correlations between H-3′′/H-4′′, H-4′′/H-5′′, and H-7′′/H-
8′′, and the HMBC correlations from H-3′′ to C-1′′ and C-9′′, H-4′′ to C-2′′
and C-6′′, H-5′′ to C-3′′, C-6′′, C-7′′, and C-10′′, H-7′′ to C-5′′ and C-10′′, H-
8′′ to C-6′′ and C-7′′, H-9′′ to C-1′′, C-2′′, and C-3′′, and H-10′′ to C-6′′ and
C-7′′ suggested the presence of a 2,6-dimethyl-8-hydroxy-2,6-octadie-
noyl group. The location of this group was confirmed by the HMBC
correlation from H-6 to C-1′′, and 2 was identified as 6-O-(2,6-dimethyl-
8-hydroxy-2,6-octadienoyl)-arbutin.
Compound 3 was obtained as a white powder with a molecular for-
mula of C23H32O9, determined based on the HRESIMS data (m/z
451.1975 [M-H]- calcd for 451.1968). The 1D and 2D NMR data showed
similar patterns to those of 2, except for the presence of a methoxy group
at C-8′′ instead of a hydroxyl group. Significant changes in the chemical
shifts of C-6′′ (δC 140.8, +2.3 ppm), C-7′′ (δC 122.6, ꢀ 3.1 ppm), and C-8′′
(δ 69.7, +10.3 ppm) were observed compared to those of 2. The posi-
C
Fig. 1. Cytotoxic (A) and tyrosinase inhibition activities (B) of eight EtOAc sub-
fractions; VEE1–8 (100 mg/ml).
tion of the methoxy group at C-8′′ was confirmed by the HMBC corre-
lation between δ 3.28 (3H, s, H-11′′) and δ 69.7 (C-8′′). As a result, the
substituent attacHhed to the aglycone was deCtermined to be 2,6-dimethyl-
8-methoxy-2,6-octadienoate. Finally, the structure of compound 3 was
identified as 6-O-(2,6-dimethyl-8-methoxy-2,6-octadienoyl)-arbutin.
Compound 4 was isolated as a white powder and had the molecular
formula of C23H32O9 (HRESIMS; m/z 451.1975 [M-H]- calcd for
451.1968). Compound 4 was identified as a derivative of 7 with the
substitution of a methoxy group at C-6′′, which was confirmed by 1D and
formula, C22H28O8, based on HRESIMS analysis (m/z 419.1690 [M-H]-
calcd for 419.1706). The 1D and HSQC NMR data of 1 exhibited char-
acteristic signals at δH/δC 4.71 (1H, d, J = 7.4 Hz, H-1)/103.6 (C-1), 4.51
(1H, dd, J = 2.1 and 11.8 Hz, H-6)/65.1 (C-6), 4.24 (1H, dd, J = 7.2 and
11.8 Hz, H-6)/65.1 (C-6), 3.62 (1H, ddd, J = 2.1, 7.2 and 9.5 Hz, H-5)/
75.4 (C-5), 3.43 (H, m, H-3)/77.9 (C-3), 3.43 (H, m, H-2)/74.9 (C-2),
and 3.36 (1H, dd, J = 6.5 and 11.7 Hz, H-4)/71.9 (C-4) for the β-D-
glucosyl moiety, as well as 153.9 (C-4′), 152.3 (C-1′), 6.93 (2H, d, J =
8.9 Hz, H-2′ and 6′)/119.5 (C-2′, 6′) and 6.66 (2H, d, J = 8.9 Hz, H-3′ and
5′)/116.6 (C-3′ and 5′) for the hydroquinone group, with two hydroxyl
groups at the para position. The HMBC NMR data showed a correlation
between δH 4.71 (1H, d, J = 7.4 Hz, H-1) and δC 152.3 (C-1′), estab-
lishing the linkage of β-D-glucosyl and hydroquinone groups, and
confirmed that the compound 1 was a derivative of β-arbutin (Paw-
lowska et al., 2006). The 1D and HSQC NMR data also exhibited the
presence of two olefinic groups (δH/δC 6.82 (1H, td, J = 1.4 and 7.3 Hz,
H-3′′)/143.7 (C-3′′) and 6.40 (1H, dd, J = 10.9 and 17.7 Hz, H-7′′)/139.7
(C-7′′)), two exomethylenes (5.28 (1H, d, J = 14.3 Hz, H-8′′)/5.09 (1H,
2D NMR data. The chemical shifts of C-5′′ (δ 39.2, ꢀ 2.5 ppm), C-6′′ (δ
C
78.5, +4.8 ppm), C-7′′ (δC 144.3, ꢀ 1.6 ppm),CC-8′′ (δC 115.8, +3.3 ppm),
and C-10′′ (δ 21.9, ꢀ 6.0 ppm) confirmed the modification of C-6′′. The
C
HMBC correlation between δH 3.17 (3H, s, H-11′′) and δC 78.5 (C-6′′)
verified the location of the methoxy group. The absolute configuration
of C-6′′ in compound 4 was confirmed by the acid hydrolysis of 4 and 7.
The hydrolytic products of 4 and 7 had the same Rf values in the thin
layer chromatography (TLC) analysis (Fig. S37). The substituent
attached to the aglycone, β-arbutin, was determined to be (6S)-2,6-
dimethyl-6-methoxy-2,7-octadienoate. Consequently, 4 was identified
as 6-O-[(6S)-2,6-dimethyl-6-methoxy-2,7-octadienoyl]-arbutin.
Compound 5 was obtained as a white powder with a molecular
2