Cl2 (calcd for C53H82O17Cl2Na, 1083.4827). The molecular
formula of 11 required the 12 sites of unsaturation present in
spirastrellolide A (1), but the molecular formula of D (4) had
one more chlorine and one less hydrogen than the molecular
formula of 1. Of the 53 well-resolved resonances observed in
the 13C NMR spectrum (C6D6) of 11, all but three (C-4, C-5,
and C-6) had chemical shifts comparable to the resonances
assigned to the carbons in 8 (Table 2, Supporting Information).
Analysis of the COSY, TOCSY, ROESY, HSQC, and HMBC
data recorded for 11 showed that methylspirastrellolide D
contained a C-8 to C-47 fragment, and a C-1 to C-37 macrolide
linkage identical in all respects to those found in methylspiras-
trellolide A (8). Further 2D NMR analysis showed that the C-3
to C-7 tetrahydropyran in 11 contained a chlorine substituent
at C-4 (δ 59.8). In the COSY spectrum, the resonance at δ 3.27
assigned to H-4 showed correlations to the H-3 resonance at δ
3.82 and to a pair of geminal methylene proton resonances at δ
1.48 and 1.76, assigned to H-5 and H-5′. HMBC correlations
observed between both H-2 (δ 2.17) and H-3 (δ 3.82) and C-4
(δ 59.8) confirmed the placement of the chlorine atom at C-4.
The H-4 resonance appeared as a bs and H-3 appeared as a bd
with J ) 9.8 Hz demonstrating that H-4 was equatorial and the
chlorine atom was axial. The similarity in 13C and 1H chemical
shift assignments, coupling constants, and observed ROESY
correlations for 8 and 11 indicated that the configurations of
the rest of the stereogenic centers were identical in both
molecules.
from the C-15 resonance (δ 29.3) to proton resonances at δ
1.39 and 1.56. The H-16 and H-16′ proton resonances at δ 1.40
and 1.54 were identified on the basis of their HMBC correlations
to C-15 (δ 29.3), and the C-16 carbon resonance at δ 35.5 was
assigned on the basis of its HMQC correlations to H-16 and
H-16′. The H-15, H-15′, H-16, and H-16′ proton resonances (δ
1.39, 1.56, 1.40, and 1.54) all correlated to the resonance at δ
95.6, assigned to the C-17 ketal carbon.
The 1H NMR spectrum of methylspirastrellolide G (14)
revealed the presence of an additional singlet methyl resonance
at δ 3.20 compared to methylspirastrellolides A-F (8-13).
Methylspirastrellolide G (14) gave a [M + Na]+ ion at m/z
1063.5409 in the HRESIMS, which was 14 daltons larger than
that observed for methylspirastrellolide A (8), and was consistent
with a molecular formula of C54H85O17Cl (calcd for C54H85O17-
ClNa, 1063.5373). Comparison of the NMR data recorded for
14 with that of 8, 11, and 12 (Supporting Information Tables 1
and 2) indicated that the macrocyclic ring of 14 was identical
to 8 and that the minor structural difference lay in the side chain.
The presence of a C-46 methyl ether in 12 satisfied the data.
This was confirmed by the observation of a HMBC correlation
between the methyl resonance at δ 3.20 and the methine carbon
resonance at δ 80.7, assigned to C-46. The H-46 resonance at
δ 3.68 correlated to C-46 in the HMQC data and showed HMBC
correlations with both C-44 (δ 124.8) and C-45 (δ 31.1).
The one remaining unresolved structural feature of the
spirastrellolides was the absolute configuration at C-46. Treat-
ment of methylspirastrellolide D (11) with sodium periodate
and a catalytic amount of RuCl3 cleaved the ∆43,44 alkene to
give methylmalate containing C-46. Reaction of the methyl-
malate with MeI and K2CO3 in acetone gave dimethylmalate
that was shown by chiral GC analysis to be the R enantiomer.
Therefore, the C-46 configuration in the spirastrellolides is R.
Methylspirastrellolides C (10), D (11), and E (12) were tested
in the cell-based assay for premature mitosis (Supporting
Information) and found to have IC50 values of 0.4, 0.7, and 0.7
µM, respectively, which is comparable to that of methylspiras-
trellolide A (8) (IC50 ) 0.4 µM).
The spirastrellolides represent a unique family of marine
sponge derived macrolides that are potent protein phosphatase
2A inhibitors (IC50 ≈ 1 nM). Their general structure has a 47-
carbon linear polyketide chain incorporated into a highly
functionalized 38-membered macrolide that has tetrahydropyran,
[6,6]-spiroketal, and [5,6,6]-bis-spiroketal substructures embed-
ded in the macrocycle and a side chain terminating in a
carboxylic acid. Spirastrellolides C (3) to G (7) have revealed
additional variations in the functionalization of the polyketide
backbone. New features include the presence of an additional
alcohol at C-8 in spirastrellolide C (3), an axial chlorine
substituent at C4 in spirastrellolide D (4), and a methyl ether
in place of an alcohol at C-46 in spirastrellolide G (7). The
suite of known structural variations in the spirastrellolide family
now includes combinations of chlorine or H at C-4, OH or H
at C-8, double bond or not at C-15/C-16, chlorine or H at C-28,
and OH or OMe at C-46.
Methylspirastrellolide E (12), which was also isolated as an
optically active clear oil, gave a [M + Na]+ ion at m/z 1015.5573
in the HRESIMS that was consistent with a molecular formula
of C53H84O17 (calcd for C53H84O17Na, 1015.5606). Analysis of
the COSY, HMQC, and HMBC data recorded for methylspi-
rastrellolide E (12) (Tables 1 and 2, Supporting Information)
showed that it was identical to methylspirastrellolide A (8) in
all respects except that methylspirastrellolide E (12), as with 9
and 10, was missing the chlorine substituent found at C-28 in
8. In the COSY spectrum of 12, the resonance at δ 3.71 assigned
to H-29 showed correlations to a pair of geminal methylene
proton resonances at δ 1.17 and 1.91, assigned to H-28 and
H-28′, which were in turn correlated to a resonance at δ 3.68,
assigned to H-27, demonstrating the absence of a substituent at
1
C-28. The similarity in 13C and H chemical shift assignments
and coupling constants for the three molecules 8, 9, and 12
indicated that the configurations of the stereogenic centers that
are common to each molecule were identical.
Methyl spirastrellolide F (13) gave a [M + Na]+ ion at m/z
1051.5421 in the HRESIMS that was consistent with a molecular
formula of C53H85O17Cl (calcd for C53H85O17ClNa, 1051.5373).
The molecular formula of 13 required 11 sites of unsaturation,
one less than methylspirastrellolide A (8). Only four olefinic
methines were observed in the 13C NMR spectrum of 13,
suggesting that the missing site of unsaturation relative to 8
was due to reduction of one of the double bonds present in 8.
Analysis of the COSY, HMQC, and HMBC data recorded for
methylspirastrellolide F (13) showed that it was identical to
methylspirastrellolide A (8) except that spirastrellolide F (6),
as is the case with 9 and 10, lacked the ∆15,16 double bond.
This was confirmed by the HMBC data which showed correla-
tions from a methyl resonance at δ 0.84, assigned to Me-48, to
methine carbon resonances at δ 73.7 and 35.0, assigned to C-13
and C-14, respectively, and to a methylene carbon resonance
at δ 29.3, assigned to C-15. HMQC correlations were observed
Experimental Section
Specimens of S. coccinea were collected by hand with use of
SCUBA on walls at a depth of 2-5 m off Capucin, Guadeloupe
Channel, Dominica. Freshly collected sponge was frozen on site
and transported frozen to Vancouver. A voucher sample has been
deposited at the Zoological Museum of Amsterdam (ZMA POR.
16778).
9844 J. Org. Chem., Vol. 72, No. 25, 2007