B.-Y. Fan et al. / Tetrahedron 70 (2014) 2003e2014
2013
HRESIMS m/z 1877.0024 [MþH]þ (calcd for C89H154NO40
3.7. Preparation of Mosher’s ester
1877.0042); 1H and 13C NMR spectral data: see Tables 3 and 5.
The (S)- and (R)-MTPA ester derivatives of 11-
hydroxytetradecanoic acid methyl ester and 11-hydroxyhexa
decanoic acid methyl ester were prepared by using the advanced
Mosher ester procedure.15 Two aliquots of each compound (1 mg
3.5.8. Cus 10 (8). Colorless gum; [
a
]
27 ꢀ42.9 (c 0.18, MeOH); IR nmax
D
KBr cmꢀ1: 3443, 2932, 2856, 1729, 1641, 1517, 1463, 1384, 1075,
1044, 818; UV (MeOH) lmax (log ) 311 (3.27), 244 (4.00), 204
3
(4.20) nm; ESIMS m/z 1833.6 [MþH]þ and 1868.4 [MþCl]ꢀ; HRE-
SIMS m/z 1832.9757 [MþH]þ (calcd for C87H150NO39 1832.9780); 1H
and 13C NMR spectral data: see Tables 3 and 5.
each in 50
m
L pyridine-d5) were transferred into two NMR tubes.
L of pyridine-d5
Then, 5 L of (S)- or (R)-MTPA chloride and 450
m
m
were added. The tubes were immediately sealed, shaken vigorously
to ensure even mixing, and standed at room temperature in a des-
iccator in 14e16 h until the reaction was complete. The 1H NMR
spectra of the corresponding ester were obtained directly from the
3.5.9. Cus 11 (9). Colorless gum; [
a
]
27 ꢀ38.8 (c 0.57, MeOH); IR nmax
D
KBr cmꢀ1: 3445, 2932, 2854, 1729, 1643, 1516, 1461, 1384, 1078,
1044, 819; UV (MeOH) lmax (log
3
) 310 (3.20), 244 (4.04), 204
NMR tubes. The selected DdH values [DdH
H-14 of 11-hydroxytetradecanoic acid methyl ester and
dH¼þ0.04, H-16 of 11-hydroxyhexadecanoic acid methyl ester)
made it possible to conclude the 11S configurations of 11-
hydroxytetradecanoic acid methyl ester and 11-hydroxyhexa
¼
d
(S)ꢀ (R)] (DdH¼þ0.06,
d
(4.29) nm; ESIMS m/z 1841.5 [MþNa]þ and 1817.5 [MꢀH]ꢀ; HRE-
SIMS m/z 1818.9611 [MþH]þ (calcd for C86H148NO39 1818.9623); 1H
and 13C NMR spectral data: see Tables 4 and 5.
D
27
3.5.10. Cus 12 (10). Colorless gum; [
a
]
ꢀ53.0 (c 0.14, MeOH); IR
decanoic acid methyl ester.
D
27
nmax KBr cmꢀ1: 3451, 2932, 2854, 1728, 1645, 1516, 1462, 1384, 1078,
11S-Hydroxytetradecanoic acid methyl ester: Colorless oil; [
a
]
D
1046, 819; UV (MeOH) lmax (log
3 ) 311 (3.29), 244 (4.03), 204
þ2.1 (c 0.11, CHCl3); 1H NMR (500 MHz, CDCl3) dH 3.67 (3H, s, OCH3),
3.59 (1H, m, H-11), 2.30 (2H, t, J¼7.5 Hz, H-2), 0.93 (3H, t, J¼7.0 Hz,
H-14); ESIMS m/z 259 [MþNa]þ.
(4.24) nm; ESIMS m/z 1847.4 [MþH]þ; HRESIMS m/z 1868.9716
[MþNa]þ (calcd for C88H151NNaO39 1868.9755); 1H and 13C NMR
spectral data: see Tables 4 and 5.
1H NMR data (500 MHz, pyridine-d5) for (S-MTPA) ester of 11S-
hydroxytetradecanoic acid methyl ester: dH 3.66 (3H, s, OCH3), 5.29
(1H, m, H-11), 2.35 (2H, t, J¼7.5 Hz, H-2), 0.88 (3H, t, J¼7.0 Hz, H-14).
1H NMR data (500 MHz, pyridine-d5) for (R-MTPA) ester of 11S-
hydroxytetradecanoic acid methyl ester: dH 3.65 (3H, s, OCH3), 5.29
3.6. Alkaline hydrolysis of 1e10
Compounds 1e10 (3.0 mg each) in 3% K2CO3/H2O (3 mL) were
refluxed at 95 ꢃC for 1 h and acidified to pH 4.0 with 1 N HCl, re-
spectively. The precipitates were filtered (the filtrate was saved)
and methylated with MeOH, catalyzed with 0.5 N H2SO4 to yield 11-
hydroxytetradecanoic acid methyl ester from 1e3 and 6e10, and
11-hydroxyhexadecanoic acid methyl ester from 4 and 5.
The filtrate was extracted with ether (3 mLꢂ2). The ether layer
was washed with H2O, dried over anhydrous Na2SO4. The presence
of acetic acid in 2, 2-methylpropanoic acid in 3 and 5 was detected
by GCeMS on a Shimadzu GCMS-QP2010 Ultra at 70 eV under the
(1H, m, H-11), 2.35 (2H, t, J¼7.5 Hz, H-2), 0.82 (3H, t, J¼7.0 Hz, H-14).
27
11S-Hydroxyhexadecanoic acid methyl ester: Colorless oil; [
a
]
D
þ1.3 (c 0.14, CHCl3); 1H NMR (500 MHz, CDCl3) dH 3.65 (3H, s,
OCH3), 3.57 (1H, m, H-11), 2.28 (2H, t, J¼7.5 Hz, H-2), 0.88 (3H, t,
J¼7.0 Hz, H-16); ESIMS m/z 309 [MþNa]þ.
1H NMR data (500 MHz, pyridine-d5) for (S-MTPA) ester of 11S-
hydroxyhexadecanoic acid methyl ester: dH 3.66 (3H, s, OCH3), 5.30
(1H, m, H-11), 2.36 (2H, t, J¼7.5 Hz, H-2), 0.86 (3H, t, J¼7.0 Hz, H-16).
1H NMR data (500 MHz, pyridine-d5) for (R-MTPA) ester of
11S-hydroxyhexadecanoic acid methyl ester: dH 3.65 (3H, s, OCH3),
5.31 (1H, m, H-11), 2.35 (2H, t, J¼7.5 Hz, H-2), 0.82 (3H, t, J¼7.0 Hz,
H-16).
following conditions (30 mꢂ0.25 mmꢂ0.25
m
m, RTX-5MS column;
D
He, 0.8 mL/min; 35 ꢃC, 3 min; 35e300 ꢃC,
10 ꢃC/min): acetic
acid (tR 4.2 min) : m/z 60 [M]þ (78), 45 (86), 43 (100); 2-
methylpropanoic acid (tR 7.8 min): m/z 88 [M]þ (9), 73 (38), 71
(2), 60 (2), 55 (5), 45 (10), 43 (100), 41 (41), 29 (7), 27 (27). The
presence of nilic acid in 1, 4, and 6e10 as well as its absolute con-
figuration were identified by the preparation of 4-
bromophenyacyl-(2R,3R)-nilate according to previously reported
procedures.10,11
3.8. Preparation of aminoalditol derivative of 11
A solution of 11 (5 mg) in 10% AcOH/EtOH (3 mL) was treated
with p-anisidine (5 mg) and NaBH3CN (5 mg), and the reaction
mixture was allowed to stand at room temperature for 4 h. After
evaporation of the solvent in vacuo, the residue was desalted by
chromatography over Sephadex LH 20 column (MeOH), and then
purified by chromatography on silica gel column (CH2Cl2/MeOH) to
give colorless oil. The ESIMS and NMR data of the colorless oil were
superimposable on those of 12.
4-Bromophenyacyl-(2R,3R)-nilate: Colorless needles; [
a
]
27 ꢀ16.0
D
(c 0.10, CHCl3); 1H NMR (500 MHz, CDCl3) dH 7.78 (2H, br d,
J¼8.5 Hz, ArH), 7.65 (2H, br d, J¼8.5 Hz, ArH), 5.33, 5.43 (each 1H, d,
J¼16.5 Hz, CH2COAr), 3.97 (1H, dq, J¼7.0, 6.5 Hz, H-3), 2.62 (1H, dq,
J¼7.0, 7.0 Hz, H-2), 1.30 (1H, d, J¼6.5 Hz, CH3-4), 1.25 (1H, d,
J¼7.0 Hz, CH3-5).
The residues obtained from aqueous phase of 1e5 were desalted
on a Sephadex LH 20 column (MeOH), and subsequently purified by
chromatography on silica gel column (CH2Cl2/MeOH) to give 11
from 1e2, 12 from 3e5.11
3.9. Acid hydrolysis and sugar analysis of 11
Compound 11 (3 mg) was dissolved in 1 N H2SO4 (3 mL) and
heated at 90 ꢃC for 2 h. The mixture was neutralized by passing
through an ion-exchange resin (Amberlite MB-3) column, and then
concentrated to yield a residue of the sugar fraction. The residue
The aqueous phase of 6e10 was separately extracted with n-
BuOH (3 mLꢂ3). The lower layer was treated in the way as de-
scribed for that of 1e5, and yielded 12. The n-BuOH layer was
subjected to an open ODS column (MeOH/H2O, 75:25, v/v) to obtain
cuscutic acids A, D, C, B (13e16)11 for 6e9, respectively, and cuscutic
acid E (17) for 10.
was dissolved in 3 mL of dry pyridine and treated with 5 mg of
L-
cysteine methyl ester hydrochloride. After heated at 60 ꢃC for 1 h,
phenyl isothiocyanate (5
mL) was added, and the mixture was
heated at 60 ꢃC for another 1 h. The reaction mixture was analyzed
by reversed-phase HPLC, which was performed on an Agilent 1200
HPLC system (Agilent Technologies Inc.) equipped with a photodi-
Cuscutic acid E (17): Colorless gum; [
a]
27 ꢀ27.3 (c 0.24, MeOH);
D
IR nmax KBr cmꢀ1: 3453, 2929, 2854, 1638, 1401, 1075, 1042; ESIMS
m/z 857.8 [MꢀH]ꢀ; HRESIMS m/z 881.4351 [MþNa]þ (calcd for
ode array detector and an Agilent C18 column (particle size 5 mm,
C
39H70NaO20 881.4353); 1H and 13C NMR spectral data: see Tables 4
250ꢂ4.6 mm) at 30 ꢃC with isocratic elution of 25% CH3CN in 0.1%
HCOOH solution at a flow rate of 0.8 mL/min. Peaks were detected
and 5.