Sesterterpenoids from the Sponge Sarcotragus sp.
Journal of Natural Products, 2008, Vol. 71, No. 4 557
δ 2.50 (1 H, m, H-2), 2.45 (2 H, t, J ) 6.8 Hz, H-5), 2.14 (3 H, s,
H-7), 1.61 (2 H, m, H-4), 1.44 (2 H, m, H-3), 1.20 (3 H, d, J ) 7.2
Hz, 2-CH3). Authentic 2-methyl-6-oxo-heptanoic acid prepared from
2,6-dimethylcyclohexanone following the procedure reported previously
ppm; H-15, –0.026 ppm; H-16, –0.005 ppm; H-17, –0.014 to –0.010
ppm; H-18, –0.023 ppm; H-19, +0.063 ppm; H-2′, –0.015 ppm; OCH3,
0 ppm.
PGME Amidation of 12. Prepared as described for 10. We obtained
7,12,13
1
1.6 and 1.5 mg of 12R and 12S from 2.4 and 2.2 mg of 12 (mixture of
gave identical H NMR data.
The same degradation with 4 and
1
6 yielded (R)-(-)-2-methyl-6-oxo-heptanoic acid with [R]2D0 values of
–6.7 (c 0.03, MeOH) and –8.3 (c 0.06, MeOH), respectively.
Oxidative Cleavage of Sesterterpenoids to Dimethyl-2-methyl-
glutarate (2, 3, and 8). The reaction was carried out following the
general procedure for 3: 26.3 mg of RuCl3 ·xH2O was added to a
biphasic solution of 7.8 mg (0.02 mmol) of 3 and 50.3 mg (0.24 mmol)
of NaIO4 in a mixture of 1 mL of CCl4, 1 mL of MeCN, and 1.5 mL
of H2O. After vigorously stirring the mixture for 2 h at room
temperature, the solvents were removed under vacuum. The residue
was redissolved in acetone and filtered on an ODS Sep-Pak column.
One milliliter of HCl ·MeOAc was added to the filtrate under N2 and
stirred for 12 h. The solvent was removed under vacuum, and the
residue was separated by reversed-phase HPLC (20% MeOH(aq)) to
yield 1.4 mg (0.008 mmol, 40.0% yield) of dimethyl-2-methyl glutarate
at a retention time of 7.4 min (flow rate 0.5 mL/min): [R]2D0 –9.1 (c
0.1, MeOH); 1H NMR (CD3OD) δ 3.63 (6 H, s, OCH3), 2.48 (1 H, m,
H-2), 1.89 (2 H, t, J ) 7.5 Hz, H-4), 1.72 (2 H, m, H-3), 1.14 (3 H, d,
J ) 7.2 Hz, 2-CH3). Authentic glutarates prepared similarly from (R)-
(-)-2-methylglutaric acid and (S)-(+)-2-methylglutaric acid gave [R]2D0
–20.8 (c 0.53, MeOH) and +19.1 (c 0.79, MeOH), respectively. The
same process with 2 and 8 gave (R)-(-)-dimethyl-2-methylglutarate
with [R]2D0 values of –16.0 (c 0.07, MeOH) and –13.1 (c 0.15, MeOH),
respectively.
12a and 12b), respectively. 12R H NMR (CD3OD) δ 7.377–7.337
(H-1, Ar), 7.231 (H-4), 6.276 (H-2), 5.452 (H-2′), 5.087 (H-15), 3.689
(OCH3), 1.652 (H-14), 1.582 (H-9), 0.942 (H-19); 12S 1H NMR
(CD3OD) δ 7.379–7.348 (H-1, Ar), 7.234 (H-4), 6.279 (H-2), 5.466
(H-2′), 5.087 (H-15), 3.687 (OCH3), 1.666 (H-14), 1.590 (H-9), 0.878
(H-19); ∆δ (12R – 12S) H-1, Ar, –0.011 to –0.002 ppm; H-2, –0.003
ppm; H-4, –0.003 ppm; H-9, –0.008 ppm; H-14, –0.008 ppm; H-15, 0
ppm; H-19, +0.064 ppm; H-2′, –0.014 ppm; OCH3, +0.020 ppm.
Acknowledgment. We thank the Seoul Branch of the Basic Science
Research Institute, Korea, for providing mass data. J.-E.S. and K.H.J.
are the recipients of a fellowship from the Ministry of Education through
the Brain Korea 21 Project. This study was partially supported by the
Korea Ocean Research & Development Institute (grant PE97802) and
the Ministry of Maritime Affairs and Fisheries, Korea (grant PM44700).
Supporting Information Available: Antibacterial activity and
cytotoxicity against the K562 cell line and inhibitory activity against
isocitrate lyase. This material is available free of charge via the Internet
References and Notes
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1
sponding (S)-PGME amide (10S) from 1.7 mg of 10: 10R H NMR
data (CDCl3) δ 7.397–7.338 (H-1, Ar), 7.231 (H-4), 6.283 (H-2), 5.455
(H-2′), 5.154 (H-7), 5.067 (H-12), 3.690 (OCH3), 2.426 (H-5), 2.253
(H-6), 2.210 (H-20), 1.996 (H-20), 1.975 (H-11), 1.937 (H-10), 1.913
(H-15), 1.889 (H-18), 1.571 (H-9), 1.547 (H-14), 1.432–1.231 (H-16,
H-17), 0.946 (H-19); 10S 1H NMR (CDCl3) δ 7.378–7.336 (H-1, Ar),
7.231 (H-4), 6.282 (H-2), 5.466 (H-2′), 5.164 (H-7), 5.087 (H-12), 3.689
(OCH3), 2.429 (H-5), 2.264 (H-6), 2.218 (H-20), 2.009 (H-20), 1.966
(H-10), 1.987 (H-11), 1.943 (H-15), 1.917 (H-18), 1.574 (H-9, H-14),
1.476–1.280 (H-16, H-17), 0.946 (H-19); ∆δ (10R - 10S) H-1, Ar,
+0.001 to +0.002 ppm; H-2, +0.001 ppm; H-4, 0 ppm; H-5, -0.003
ppm, H-6, –0.011 ppm, H-7, –0.010 ppm, H-9, –0.003 ppm; H-10,
–0.029 ppm, H-11, –0.012 ppm; H-12, –0.020 ppm; H-14, –0.027 ppm;
H-15, –0.030 ppm; H-16, H-17, –0.044 to –0.049 ppm; H-18, –0.028
ppm; H-19, +0.064 ppm; H-20, –0.013 ppm; H-20, –0.008 ppm; H-2′,
–0.011 ppm; OCH3, +0.001 ppm.
PGME Amidation of 11. Prepared as described for 10. We obtained
1.1 and 1.4 mg of 11R and 11S from 2.3 and 2.3 mg of 11, respectively.
1
11R H NMR (CD3OD) δ 7.364–7.342 (H-1, Ar), 7.248 (H-4), 6.276
(H-2), 5.452 (H-2′), 5.093 (H-10, H-15), 3.687 (OCH3), 2.390 (H-5),
2.255 (H-20), 2.219 (H-7), 2.100 (H-11), 2.055 (H-12), 2.024 (H-20),
2.006 (H-16), 1.664 (H-9), 1.660 (H-14), 1.635 (H-6), 1.412–1.154 (H-
1
17), 0.937 (H-19); 11S H NMR data (CD3OD) δ 7.376–7.347 (H-1,
Ar), 7.249 (H-4), 6.279 (H-2), 5.467 (H-2′), 5.119 (H-10, H-15), 3.687
(OCH3), 2.396 (H-5), 2.265 (H-20), 2.101 (H-11), 2.055 (H-12), 2.023
(H-20), 2.011 (H-16), 1.940 (H-18), 1.671 (H-9), 1.668 (H-9, H-14),
1.644 (H-6), 1.426–1.164 (H-17), 0.874 (H-19); ∆δ (11R – 11S) H-1,
Ar, –0.120 to –0.005 ppm; H-2, –0.003 ppm; H-4, –0.001 ppm; H-5,
–0.006 ppm; H-6, –0.009 ppm; H-7, –0.046 ppm; H-9, –0.007 ppm;
H-10, –0.026 ppm; H-11, –0.001 ppm; H-12, 0 ppm; H-14, –0.008
NP0780147