Journal of Natural Products
Article
alignment contained fragments of the genes cytochrome b,
cytochrome oxidase subunit I, 12S rRNA, 16S rRNA, and ND1. The
sequences were resolved on an ABI 3130XL automated sequencer
(Applied Biosystems). All newly determined sequences were
submitted to GenBank (accession numbers KF426665-KF426724).
The sequences were checked, and reading errors were corrected
manually in CodonCode Aligner (CodonCode Corp.). The align-
ments were done in MEGA 521 and were unambiguous (only a few
gaps required in the rRNA genes, mostly to accommodate the
outgroup sequences). MrModeltest version 2.322 was used to select
the best fitting nucleotide model of evolution under the Akaike
information criterion (a GTR+I+G model). Phylogenetic analysis
based on Bayesian inference was computed with MrBayes v3.0b423
using Markov chain Monte Carlo (MCMC) sets for 20 × 106
generations and sampled every 1000 generations. The trees
corresponding to the first 10 × 106 generations were conservatively
discarded as burn-in after empirically assessing the log-likelihood
values of the sampled trees.
= 6.3 Hz), 0.81 (3H, d, J = 6.8 Hz); 13C NMR (100 MHz, CDCl3) δ
174.3, 72.8, 34.6, 32.5, 31.5, 30.2, 28.1, 23.5, 21.0, 20.7, 19.3; EIMS
(70 eV) m/z (%) 184 (1) [M]+, 169 (1), 124 (8), 112 (50), 96 (20),
83 (61), 69 (44), 55 (100); HREIMS m/z 184.1458 (calcd for
C11H20O2, 184.1463); I = 1336.
(3S)-3-Methylhex-5-en-2-yl hex-5-enoate (24). (3S)-3-Methylhex-
5-en-2-ol (23) (0.19 g, 1.7 mmol), 5-hexenoic acid (0.18 g, 1.57
mmol), and DMAP (21 mg, 0.17 mmol) were added to absolute
CH2Cl2 (10 mL) at 0 °C. Then EDC·HCl (0.33 g, 1.75 mmol) was
added to the above solution.24 The reaction mixture was stirred at 0
°C for 1 h and at rt for 5 h until the complete consumption of the
alcohol (23) was observed by TLC. The reaction mixture was diluted
with Et2O (40 mL) and washed with saturated NaHCO3 (2 × 30 mL).
The organic phase was dried using MgSO4, and the crude product was
purified by column chromatography to yield (3S)-3-methylhex-5-en-2-
yl hex-5-enoate (24) (0.26 g, 1.23 mmol, 73%).
Rf = 0.4 (pentane/Et2O, 30:1); 1H NMR (300 MHz, CDCl3) δ 5.76
(2H, m), 5.01 (4H, m), 4.85 (1H, m), 2.29 (2H, t, J = 7.6 Hz), 2.19
(1H, m), 2.09 (2H, m), 1.89 (1H, m), 1.73 (3H, m), 1.16 (3H, d, J =
7.0 Hz), 0.91 (3H, d, J = 8.1 Hz); 13C NMR (75 MHz, CDCl3) δ
173.1, 137.7, 136.7, 116.2, 115.3, 73.2, 37.6, 37.2, 34.0, 33.1, 24.2, 17.0,
16.3; EIMS (70 eV) m/z (%) 166 (1), 128 (1), 114 (4), 99 (2), 97
(42), 81 (27), 72 (2), 69 (47), 68 (8), 55 (87), 43 (22), 41 (100), 39
(39).
Synthesis. (S)-Hex-5-en-2-yl (S)-4-methylhex-5-enoate (30). (S)-
4-Methylhex-5-enoic acid (29, 40 mg, 0.31 mmol), (S)-hex-5-en-2-ol
(33, 36 mg, 0.36 mmol), and DMAP (4 mg, 0.03 mmol) were
dissolved in 10 mL of absolute CH2Cl2 and cooled to 0 °C. N-Ethyl-
N′-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC, 76
mg, 0.4 mmol) was added in one portion, and the reaction was
stirred for 1 h at 0 °C and for 2 h at room temperature (rt), similar to
the procedure described by Patel et al.24 Then the reaction mixture
was diluted with tert-butyl methyl ether, washed with saturated
NaHCO3, and dried with MgSO4. After solvent removal under
reduced pressure the crude product was purified by column
chromatography on silica gel, yielding pure (S)-hex-5-en-2-yl (S)-4-
methylhex-5-enoate (30, 34 mg, 0.29 mmol, 92%).
(5Z,8S)-8-Methyl-5-decen-9-olide (25). (3S)-3-Methylhex-5-en-2-yl
hex-5-enoate (24) (77 mg, 0.36 mmol) was dissolved in dry toluene
(250 mL), and hexafluorobenzene (4.4 g, 23 mmol) was added to the
above solution. Then Grubbs II catalyst (1,3-bis(2,4,6-trimethylphen-
yl)-2-imidazolidinylidene)dichloro(phenylmethylene)
(tricyclohexylphosphine)ruthenium (40 mg, 0.076 mmol) was added,
and the reaction mixture was heated to 80 °C for 3 h. The reaction was
cooled to rt and washed with saturated NaHCO3. The organic phase
was dried using MgSO4. The organic solvents were evaporated, and
the Grubbs catalyst was filtered off on a silica gel filled microcolumn.
The column was washed (four column volumes) with pentane/Et2O
(40:1). The column fractions were evaporated, and the crude prodcut
was purified by column chromatography to yield (5Z,8S)-8-methyl-5-
decen-9-olide (25) (30 mg, 0.16 mmol, 45%).
1
Rf = 0.53 (pentane/tert-butyl methyl ether, 40:1); H NMR (200
MHz, CDCl3) δ 5.52−5.96 (2H, m), 4.81−5.12 (5H, m), 2.20−2.33
(2H, m), 1.96−2.19 (3H, m), 1.45−1.80 (4H, m), 1.15−1.25 (3H, d, J
= 6.1 Hz), 0.97−1.04 (3H, d, J = 6.8 Hz); 13C NMR (50 MHz,
CDCl3) δ 173.4, 143.5, 137.8, 114.9, 113.5, 70.2, 37.5, 35.1, 32.5, 31.5,
29.7, 20.1, 19.9; EIMS (70 eV) m/z (%) 153 (1), 128 (40), 111 (36),
82 (57), 67 (72), 55 (100), 41 (49).
1
(4S,5Z,9S)-4-Methyl-5-decen-9-olide (31). A solution of (S)-hex-5-
en-2-yl (S)-4-methylhex-5-enoate (30, 20 mg, 0.095 mmol) and
hexafluorobenzene (1.8 mL, 6 mmol) was prepared in 150 mL of dry
toluene according to the procedure of Rost et al.25 The Hoveyda−
Grubbs-II catalyst dichloro[1,3-bis(2,4,6-trimethylphenyl)-2-
imidazolidinylidene](2-isopropoxyphenylmethylene)ruthenium(II)
(12 mg, 0.019 mmol) was added to this solution, and the reaction was
stirred for 3 h at 80 °C. The reaction was quenched by the addition of
saturated NaHCO3 solution after cooling to rt, and the phases were
separated. The organic layer was dried with MgSO4, and the solvent
was removed under reduced pressure. After column chromatographic
purification on silica gel (4S,5Z,9S)-4-methyl-5-decen-9-olide (31, 12
mg, 0.066 mmol, 69%) was obtained.
Rf = 0.52 (pentane/Et2O, 10:1); H NMR (300 MHz, CDCl3) δ
5.36 (2H, m), 4.71 (1H, qd, J = 6.5, 4.1 Hz), 2.27 (3H, m), 2.17 (2H,
m), 1.91 (2H, m), 1.73 (2H, m), 1.20 (3H, d, J = 6.4 Hz), 0.98 (3H, d,
J = 6.6 Hz); 13C NMR (75 MHz, CDCl3) δ 175.3, 133.9, 131.0, 75.0,
38.3, 33.7, 32.2, 26.5, 26.0, 17.3, 14.1; EIMS (70 eV) m/z (%) 182
(12) [M]+, 164 (4), 149 (5), 138 (14), 126 (12), 110 (25), 99 (89),
95 (32), 93 (17), 84 (37), 81 (71), 79 (40), 68 (26), 67 (81), 55 (76),
53 (41), 41 (100), 39 (80).
(8S,9RS)-8-Methyl-9-decanolide (6). (5Z,8S)-8-Methyl-5-decen-9-
olide (25) (30 mg, 0.16 mmol) was dissolved in MeOH (30 mL,
HPLC grade), and 10 mg of 10% palladium on activated carbon was
added. Then hydrogen gas was passed into the reaction solution at a
pressure of 2 bar for 5 h. Next the catalyst was filtered off on a Celite-
filled microcolumn, and the column was washed with MeOH. The
MeOH fractions were collected and evaporated to yield (8S,9RS)-8-
methyl-9-decanolide (6) (23 mg, 0.12 mmol, 76%). The ratio (8S,9S):
(8S,9R) was 1:0.7.
1
Rf = 0.55 (pentane/tert-butyl methyl ether, 19:1); H NMR (400
MHz, CDCl3) δ 5.28−5.46 (1H, m), 4.98−5.15 (1H, m), 4.61 (1H,
m), 2.16−2.25 (2H, m), 2.10−2.16 (1H, m), 1.94−2.05 (2H, m),
1.46−1.58 (4 H, m), 1.09 (3H, d, J = 6.5 Hz), 1.01 (3H, d, J = 7.0 Hz);
13C NMR (100 MHz, CDCl3) δ 175.8, 132.6, 129.0, 71.1, 34.5, 33.1,
32.5, 32.0, 29.8, 21.7, 15.2; EIMS (70 eV) m/z (%) 182 (5) [M]+, 140
(5), 125 (7), 109 (15), 85 (100), 67 (51), 55 (31).
[α]2D1.5 −8.3 (c 0.7, CHCl3); H NMR (600 MHz, CDCl3) δ 4.8
1
(1H, qd, J = 6.8, 3.4 Hz), 4.4 (1H, dq, J = 10.4, 6.2 Hz) 2.4 (2H, m)
2.2 (1H, ddt, J = 10.8, 7.2, 3.6 Hz), 2.1 (1H, m), 2.0 (2H, m), 1.8 (1H,
m), 1.7 (1H, m), 1.6 (2H, m), 1.4 (8H, m), 1.2 (4H, m), 1.1 (3H, d, J
= 6.2 Hz), 1.1 (3H, d, J = 6.8 Hz), 0.8 (3H, d, J = 7.0 Hz), 0.7 (3H, d, J
= 7.0 Hz); 13C NMR (151 MHz, CDCl3) (8S,9S)-6 δ 173.3, 75.7, 35.7,
35.1, 30.6, 27.7, 24.2, 22.5, 20.4, 19.8, 12.8; (8S,9R)-6 δ 174.0, 77.7,
40.0, 34.7, 29.7, 27.0, 25.9, 22.6, 20.6, 18.9, 17.8; EIMS (70 eV) m/z
(%) 184 (1) [M]+, 166 (2), 148 (2), 140 (11), 123 (2), 112 (17), 109
(3), 98 (62), 94 (6), 83 (19), 81 (12), 69 (24), 67 (14), 56 (26), 55
(71), 53 (13), 45 (14), 42 (46), 41 (100), 39 (62); HREIMS m/z
(4R,9S)-4-Methyldecan-9-olide (4R,9S-4). A solution of
(4S,5Z,9S)-4-methyl-5-decen-9-olide (31) (12 mg, 0.066 mmol) in 1
mL of absolute MeOH was prepared in a 1 mL vial, and 2 mg of 10%
palladium on activated charcoal was added to hydrogenate the double
bond according to the procedure of Kitahara et al.7 Hydrogen was
bubbled through this solution with a pressure of 1 bar for 5 h. Then
the catalyst was filtered off, and methanol was carefully evaporated in a
gentle stream of nitrogen. Pure (4R,9S)-4-methyldecan-9-olide (4, 9
mg, 0.049 mmol, 74%) was obtained.
184.1466 (calcd for C11H20O2 184.1463); I(8S,9S)‑6 = 1346, I(8S,9R)‑6
=
[α]D26.7 +10.3 (c 0.74, CH2Cl2); H NMR (400 MHz, CDCl3) δ
1329.
1
4.88−5.00 (1H, m), 2.07−2.21 (2H, m), 1.77−1.96 (2H, m), 1.63−
1.75 (2H, m), 1.51−1.62 (3H, m), 1.25−1.43 (4H, m), 1.20 (3H, d, J
6-Methyloctan-2-ol (36). 3-Methylmagnesium bromide was
prepared by dropwise addition of 1-bromo-3-methylpentane (35,
1556
dx.doi.org/10.1021/np400131q | J. Nat. Prod. 2013, 76, 1548−1558