Glycolipids from sponges. Part 16.1 discoside, a rare myo-Inositol-containing glycolipid from the caribbean sponge Discodermia dissoluta

Article abstract of DOI:10.1021/np050241q

Discoside (1a), a glycolipid composed of 4,6-O-diacylated mannose attached to the 2-hydroxyl group of a myo-inositol unit, was isolated as a mixture of homologues from the marine sponge Discodermia dissoluta. The complete stereostructure of this new glycolipid was solved by interpretation of mass spectrometric and NMR data and CD analysis of degradation products.

Full text of DOI:10.1021/np050241q

J. Nat. Prod. 2005, 68, 1527-1530
1527
Glycolipids from Sponges. Part 16.1 Discoside, a Rare myo-Inositol-Containing
Glycolipid from the Caribbean Sponge Discodermia dissoluta
Lucia Barbieri, Valeria Costantino, Ernesto Fattorusso,* and Alfonso Mangoni
Dipartimento di Chimica delle Sostanze Naturali, Universita` di Napoli “Federico II”,
Via D. Montesano 49, 80131 Napoli, Italy
Received July 6, 2005
Discoside (1a), a glycolipid composed of 4,6-O-diacylated mannose attached to the 2-hydroxyl group of a
myo-inositol unit, was isolated as a mixture of homologues from the marine sponge Discodermia dissoluta.
The complete stereostructure of this new glycolipid was solved by interpretation of mass spectrometric
and NMR data and CD analysis of degradation products.
Inositol-containing lipids are key membrane constituents
and play important roles in essential metabolic processes
in plants, animals, and some bacteria.2 Phosphatidylinosi-
tols (PI), for example, are well known to be the anchor that
links a variety of proteins to the external leaflet of the
plasma membrane via a glycosyl bridge.
In the course of our ongoing efforts to study the glycolip-
ids from marine sponges, we have found a new inositol-
containing glycolipid (1a), which we have named discoside.
Discoside is the first example of a 4,6-O-diacylated man-
nose attached to the 2-hydroxyl group of a myo-inositol unit
[2-O-(4,6-di-O-acyl-R-D-mannopyranosyl)-myo-inositol]. The
mannopyranosyl-myo-inositol partial structure is a well-
known building block of phosphatidylinositol mannosides
(PIMs) and of their multiglycosylated form, lipomannans
(LMs), which are found in the cell walls of Mycobacteria
and related species and exhibit a wide spectrum of immu-
noregulatory effects.2,3
has been suggested that this glycolipid is involved in the
biosynthesis of PIMs. Since this first report, no other
members of this class of glycolipids have been described.
Results and Discussion
The CHCl3-MeOH-soluble extract of the marine sponge
D. dissoluta (Schmidt 1880, Porifera, class Demospongiae,
order Theonellidae, family Discodermiidae) collected around
Berry Island (Bahamas) was partitioned between BuOH
and H2O. The organic fraction was successively purified
by reversed-phase chromatography followed by direct-
phase chromatography, yielding a crude fraction containing
only glycolipids. This fraction was acetylated with Ac2O in
pyridine. This derivatization procedure is very useful in
studying glycolipids. In fact, the nonpolar peracetylated
glycolipid mixture is easy to purify on normal-phase HPLC.
In addition, resonance assignment in the homonuclear
NMR spectra of peracetylated glycolipids is made easier
because of the better signal dispersion that allows also to
discriminate between ether and ester oxymethine proton
resonances on the basis of their different chemical shift
range (δ 3.5-4.5 and 4.7-5.7, respectively).
The peracetylated glycolipid fraction was chromato-
graphed by HPLC on a SiO2 column using n-hexane-
EtOAc (6:4). Discoside was isolated as its peracetyl deriva-
tive 1b. Unfortunately, compound 1b could not be deacetyl-
ated to give the natural discoside 1a because of the
presence of the ester-linked acyl chains. We tried to isolate
discoside 1a from the nonacetylated crude glycolipid frac-
tion, but we did not succeed because of its low natural
concentration and the difficulty of separating nonacetylated
glycolipids.
ESIMS of 1b showed the presence of three ion peaks [M
+ Na]+ differing from each other by CH2 (14 amu) at m/z
1219, 1205, and 1191, indicating that discoside is actually
a mixture of homologues, which were not further separated.
HREIMS of the most intense peak at m/z 1205.7159
supported the molecular formula C63H106O20.
Inspection of the 1H NMR spectrum of 1b in CDCl3
suggested that discoside is a glycolipid because of (i) a 6H
methyl triplet at δ 0.88 attributable to two linear alkyl
chains; (ii) a doublet at δ 0.83, which integrated for a
nonintegral number of internal methyl branches and,
therefore, indicated that the homologues have different
branching; (iii) a broad band of resonances at δ 1.25
indicative of long aliphatic hydrocarbon chains; (iv) seven
acetyl methyl resonances between δ 2.16 and 1.98; and (v)
a cluster of carbinol proton resonances between δ 4.00 and
5.60.
The only close analogue of 1a is 1-O-pentadecanoyl-2-
O-(6-O-heptadecanoyl-R-D-mannopyranosyl)-myo-inositol,4
isolated in 1968 from various strains of Propionibacterium,
where it constitutes up to 40% of the total lipid fraction. It
* Corresponding author. Phone: +39-081-678-503. Fax: +39-081-678-
552. E-mail: ernesto.fattorusso@unina.it.
10.1021/np050241q CCC: $30.25
© 2005 American Chemical Society and American Society of Pharmacognosy
Published on Web 09/28/2005

1528 Journal of Natural Products, 2005, Vol. 68, No. 10
Barbieri et al.
Table 1. 1H and 13C NMR Data of Discoside Peracetate 1b (500 MHz)
CDCl3
C6D6
pos.
δH (mult., J [Hz])a
δC (mult.)b
69.8 (CH)
δH (mult., J [Hz])c
δC (mult.)d
70.3 (CH)
1
5.00 (dd, 10.5, 2.3)
4.29 (t, 2.3)
4.88 (dd, 10.5, 2.4)
2
76.3 (CH)
70.6 (CH)
69.7 (CH)
70.9 (CH)
69.5 (CH)
99.6 (CH)
69.8 (CH)
68.8 (CH)
65.5 (CH)
69.8 (CH)
61.9 (CH2)
4.17 (t, 2.4)
77.3 (CH)
70.8 (CH)
70.7 (CH)
71.3 (CH)
70.1 (CH)
100.0 (CH)
70.4 (CH)
69.3 (CH)
66.0 (CH)
70.7 (CH)
62.1 (CH2)
3
5.08 (dd, 10.5, 2.3)
5.53 (dd, 10.5, 9.8)
5.19 (t, 9.8)
5.49 (dd, 10.5, 9.8)
4.96 (d, 1.6)
5.37 (br s)
5.01 (dd, 10.5, 2.4)
4
5.91f (t, 10)
5
5.33 (t, 9.7)
6
5.91f (t, 10)
1′
4.98 (d, 1.8)
2′
5.66 (dd, 3.1, 1.8)
5.83 (dd, 10.1, 3.1)
5.92f (t, 10)
3′
5.41e
4′
5.42e
5′
4.18 (m)
4.26 (dd, 12.2, 3.8)
4.09 (dd, 12.2, 2.1)
4.56 (br d, 9.7)
4.60 (dd, 12.1, 3.7)
4.48 (dd, 12.1, 1.5)
6′a
6′b
1′′
2′′
3′′
1′′′
2′′′
3′′′
Ac’s
172.4 (CdO)
34.1 (CH2)
25.0 (CH2)
173.2 (CdO)
34.0 (CH2)
24.8 (CH2)
20.7-20.4 (CH3)
172.4 (CdO)
34.2 (CH2)
25.2 (CH2)
173.0 (CdO)
34.4 (CH2)
25.2 (CH2)
20.4-19.9 (CH3)
2.31 (m)
1.61 (m)
2.11 (m)
1.53 (m)
2.34 (m)
1.62 (m)
2.37 (m)
1.72 (m)
1.93 (s), 1.88 (s), 1.66 (12H, s),
1.58 (s)
2.14 (s), 2.09 (s), 2.07 (s), 2.03 (s),
2.02 (s), 2.01 (s), 1.99 (s)
169.8-169.2 (CdO)
169.6-168.9 (CdO)
a Alkyl chain 1H signals (CDCl3): δ 1.25 (broad band, alkyl chain protons), 0.88 (t, J ) 7.0, H3-18), 0.83 (d, J ) 6.4, H3-18). b Alkyl
chain 13C signals (CDCl3): 31.9 (CH2, C-16), 22.7 (CH2, C-17), 14.0 (CH3, C-18); 10-Me branched chains: 37.2 (CH2, C-9 and C-11), 32.8
(CH, C-10), 27.1 (CH2, C-8 and C-11), 19.7 (CH3, C-19). c Alkyl chain 1H signals (C6D6): δ 1.32 (broad band, alkyl chain protons), 0.94 (t,
J ) 6.4, H3-18), 0.91 (d, J ) 6.8, H3-18). d Alkyl chain 13C signals (CDCl3): 32.3 (CH2, C-16), 23.0 (CH2, C-17), 14.3 (CH3, C-18); 10-Me
branched chains: 37.6 (CH2, C-9 and C-11), 33.3 (CH, C-10), 27.6 (CH2, C-8 and C-11), 19.9 (CH3, C-19). e Non-first-order multiplet.
f Coupling constants were measured from a row of the HSQC spectrum.
As usual for glycolipid molecules, many resonances
overlapped, preventing their analysis. To circumvent this
problem, NMR spectra were recorded using two different
the HSQC clearly pointed to the equatorial orientation of
H-1′ and, therefore, to the R anomeric configuration of the
sugar unit.
1
solvents (CDCl3 and C6D6).5 From the H NMR spectrum
Six oxymethine resonances in the mid-field region of the
1H NMR spectrum remained to be interpreted. These
resonances were part of the same spin system, as deduced
from the COSY spectrum, and originated from the six
cyclically arranged protons of an inositol. In fact, the proton
at δ 4.29 (CDCl3, H-2) was coupled with two protons at δ
5.05 (H-1) and 5.08 (H-3), which were in turn coupled with
a signal at δ 5.49 (H-6) and a signal at δ 5.53 (H-4),
respectively. Finally, both H-6 and H-4 were coupled with
a signal resonating at δ 5.19 (H-5). Analysis of the coupling
constants allowed establishment of the relative configura-
tion of the inositol moiety. The coupling constants between
H-1/H-6, H-3/H-4, H-4/H-5, and H-5/H-6 (see Table 1)
indicated the trans-diaxial nature of these protons, while
the small coupling constant (J ) 2.3 Hz) of H-2 with H-3
and H-1, respectively, accounted for its equatorial orienta-
tion. The above data are consistent with a myo-inositol. The
relatively upfield chemical shift of H-2 (δ 4.29) suggested
that the myo-inositol is glycosylated at C-2, as confirmed
by a cross-peak between H-1′ and C-2 and between H-2
and C-1′ in the HMBC experiments in both solvents.
Once the gross structure was defined, the location of the
two acyl chains was established on the basis of HMBC data.
In fact, the carbonyl carbon atom at δ 172.4 (CDCl3, C-1′′)
of one fatty acyl chain, identified from its HMBC correla-
tion peak with the R-methylene protons at δ 2.31 (H-2′′),
was also coupled with the mannose proton H-4′ (δ 5.42).
Likewise, the carbonyl carbon atom of the second fatty acyl
chain (δ 173.2, C-1′′′) was coupled with the R-methylene
protons at δ 2.33 (H-2′′′) as well as with H-6′a (δ 4.26).
of 1b in C6D6 two pairs of R-carbonyl methylene protons
at δ 2.37 and 2.11, respectively, indicative of two fatty acid
residues, were distinguished.
In the 13C NMR spectrum in C6D6, the diagnostic value
at δ 100.0, indicative of an anomeric carbon atom (C-1′),
confirmed the presence of one sugar moiety. Building up
the saccharide structure required a series of sequential
steps: first, data obtained from a HSQC NMR experiment
permitted assignment of the relevant anomeric proton at
δ 4.97 (C6D6, H-1′). Then, the H-1′ resonance was the
starting point to identify, in sequence, four methine protons
at δ 5.66 (H-2′), 5.83 (H-3′), 5.92 (H-4′), and 4.57 (H-5′) and
two methylene protons at δ 4.61 (H-6′a) and 4.48 (H-6′b),
respectively, by means of COSY correlation peaks. These
data are in accordance with a hexose structure. The
relatively upfield chemical shift of H-5′ established that
the hexose is in the pyranose form.
At this point, an accurate analysis of coupling constants
was needed to identify the nature of the hexopyranose. The
large (J ) 10 Hz) coupling constant6 between H-5′ and H-4′
indicated the trans-diaxial nature of these protons. H-3′
showed one large (J ) 10.1 Hz) and one small (J ) 3.1 Hz)
coupling constant, showing H-3′ to be an axial proton
flanked by the axial H-4′ and the equatorial H-2′ proton.
These data revealed the manno configuration of the hex-
opyranose unit.
The equatorial position of H-2′ prevented the anomeric
configuration of the mannopyranose from being determined
on the basis of homonuclear coupling constant values.
Because the chemical shifts of H-4′ and H-3′ were nearly
coincident in the spectra recorded in CDCl3, these data did
not positively prove that the fatty acyl chain was linked to
O-4′ and not to O-3′. Therefore, the HMBC experiment in
C6D6 was also analyzed. The long-range coupling between
1
However, it is known that the JCH coupling constant of
an axial anomeric proton is approximately 160 Hz, while
that of an equatorial anomeric proton is ∼170 Hz.7 The
coupling constant between H-1′ and C-1′ (J ) 174 Hz) in

Glycolipid from the Sponge Discodermia dissoluta
Journal of Natural Products, 2005, Vol. 68, No. 10 1529
the carbon at δ 172.3 (C-1′′) and the proton at δ 5.92
(H-4′) demonstrated that one fatty acyl group was indeed
linked to O-4′.
discoside and the myo-inositol-containing glycolipid of
bacterial origin, it is reasonable to suppose that also
discoside could be produced by symbionts associated with
the sponge.
The nature and the relative amounts of the fatty acyl
chains of 1b were identified using chemical degradation
and GC-MS. Acid-catalyzed methanolysis of 1b liberated
the fatty acid methyl esters, methyl mannoside, and myo-
inositol. The reaction mixture was partitioned between
CHCl3 and H2O, giving an organic layer containing a
mixture of fatty acid methyl esters and an aqueous layer
containing methyl mannoside and myo-inositol.
The mixture of fatty acid methyl esters was subjected
to GC-MS analysis, and three different compounds were
identified on the basis of their GC retention times and
mass fragmentation: methyl octadecanoate (33%), methyl
10-methyloctadecanoate (51%), methyl 12-methyloctade-
canoate (16%). The unbranched compound showed GC
retention time and mass spectra that matched those of an
authentic sample. As for methyl 12-methyloctadecanoate
(M+ ) m/z 312), methyl branch positions were indicated
by the mass spectrometric fragmentation pattern:8 two
relatively intense peaks separated by 28 amu at m/z 199
(C12H23O2) and 227 (C14H27O2), originating from R-cleav-
ages with respect to the tertiary carbon atoms carrying the
Experimental Section
General Experimental Procedures. High-resolution ES-
IMS spectra were obtained on a Micromass QTOF Micro mass
spectrometer, dissolving the sample in MeCN-H2O (1:1) with
0.1% TFA. ESIMS experiments were performed on an Applied
Biosystem API 2000 triple-quadrupole mass spectrometer. The
spectra were recorded by infusion into the ESI source using
MeOH as the solvent. Optical rotations were measured at 589
nm on a Perkin-Elmer 192 polarimeter using a 10 cm microcell.
CD spectra were recorded on a Jasco J-710 spectrophotometer
1
using a 1 cm cell. H and 13C NMR spectra were determined
on a Varian Unity Inova spectrometer at 500.13 and 125.77
MHz, respectively; chemical shifts were referenced to the
residual solvent signal (CDCl3: δH ) 7.26, δC ) 77.0; C6D6:
1
δH ) 7.15, δC ) 128.0). Homonuclear H connectivities were
determined by COSY experiments. Through-space 1H connec-
tivities were evidenced using a ROESY experiment with a
mixing time of 500 ms. Coupling constants of overlapping
1
signals in the H spectrum were measured from the rows of
the HSQC. The reverse multiple-quantum heteronuclear cor-
relation (HSQC) spectra were recorded optimized for an
average 1JCH of 140 Hz. The gradient-enhanced multiple-bond
heteronuclear correlation (HMBC) experiment was optimized
for a 3JCH of 8 Hz. GC-MS spectra were recorded on a Hewlett-
Packard 5890 gas chromatograph with a mass selective
detector MSD HP 5970 MS, a split/splitness injector, and a
fused-silica column, 25 m × 0.20 mm HP-5 (cross-linked 25%
Ph Me silicone, 0.33 mm film thickness); the temperature of
the column was varied, after a delay of 3 min from the
methyl branch, and two peaks at m/z 195 (C14H27O2
-
MeOH) and 177 (C14H27O2 - MeOH - H2O). Analogously,
the methyl branching of methyl 10-methyloctadecanoate
(M+ ) m/z 312) was indicated by the peaks at m/z 171
(C10H19O2), 199 (C12H23O2), 167 (C12H23O2 - MeOH), and
149 (C12H23O2 - MeOH - H2O).
After structure 1b was fully established, it remained to
verify whether any of the acetyl groups in 1b were already
present in the native glycolipid. This was accomplished by
subjecting a small portion of the crude glycolipid fraction
to acetylation with trideuteroacetic anhydride instead of
acetic anhydride.9 The 1H NMR spectrum of the derivative
1c was identical to that of 1b except for the absence of the
seven acetyl methyl singlets, showing that none of the
acetyl groups in 1b were present in the natural product
1a. In addition, in the ESIMS spectrum of the pertrideu-
teroacetate derivative 1c, the three [M + Na]+ pseudomo-
lecular ion peaks were present at m/z 1212, 1226, and 1240,
21 amu higher than the corresponding ions of 1b.
The absolute configuration of the mannopyranose unit
was established as D using a circular dichroism (CD)
method. The aqueous layer from the methanolysis, con-
taining methyl mannosides and the meso myo-inositol, was
perbenzoylated with benzoyl chloride in pyridine, and
methyl R-mannopyranoside perbenzoate was isolated by
normal-phase HPLC and identified from its 1H NMR
spectrum. The CD spectrum of methyl R-mannopyranoside
perbenzoate obtained from discoside matched that of an
authentic sample of methyl R-D-mannopyranoside perben-
zoate.
In summary, we reported the isolation and the complete
stereostructure determination of discoside, a unique gly-
colipid containing a myo-inositol mannoside. Such com-
pounds have never been reported from marine sponges,
since the only close analogue of discoside reported was
isolated from various strains of Propionibacterium. Recent
studies suggested that secondary metabolites may be
produced by symbiotic microorganisms rather than by the
sponges to which they have been attributed.10 It is worth
noting that the most important secondary metabolite
isolated form D. dissoluta, the antitumor polyketide dis-
codermolide,11 is thought to be produced by bacterial
symbionts.12 Because of the strong similarity between
injection, from 150 to 280 °C with a slope of 10 °C min-1
;
quantitative determination was based on the area of the GC
peaks. High-performance liquid chromatographies (HPLC)
were achieved on a Varian Prostar 210 apparatus equipped
with an Varian 350 refractive index detector or a Varian 325
UV detector.
Collection. Specimens of D. dissoluta (Porifera, class
Demospongiae, order Theonellidae, family Discodermiidae)
were collected by scuba (depth 23 m) during the third “Pawlik
Expedition” (July 2000) along the coast of Little San Salvador
(Bahamas) and identified by Prof. M. Pansini, University of
Genova. A reference sample (#28-00) has been deposited at
the Istituto di Zoologia, Genova, Italy. The samples were stored
at -20 °C until extraction.
Extraction. The frozen sponge sample of D. dissoluta
#28-00 (36 g of dry weight after extraction) was blended in
MeOH, then in sequence extracted with MeOH, MeOH-CHCl3
(2:1), MeOH-CHCl3 (1:2), and CHCl3.
Glycolipid Isolation Procedure. The MeOH extracts
were partitioned between BuOH and H2O. The BuOH phase
was concentrated in vacuo and combined with the CHCl3
extract. The organic phases (35.97 g) were subjected to
chromatography on a column packed with RP-18 by elution
with a gradient of H2O-MeOH to CHCl3. The fraction
eluted with CHCl3 (7.5 g) was further chromatographed on a
SiO2-packed column eluted with a gradient of n-hexane-
EtOAc (9:1) to MeOH. The fraction eluted with EtOAc-MeOH
(7:3, 345 mg) was composed only of glycolipids. This fraction
was acetylated with Ac2O in pyridine and chromatographed
by HPLC on a SiO2 column using n-hexane-EtOAc (6:4) to
afford 7.5 mg of peracetylated discoside (1b).
25
Discoside Peracetate (1b): colorless oil, [R]D +12°
(CHCl3, c 0.5); 1H and 13C NMR, Table 1; ESIMS m/z 1219,
1205, 1191, [M + Na]+ series; HRESIMS m/z 1205.7159 (calcd
for C63H106NaO20, 1205.7170).
Fatty Acyl Chains Determination. Compound 1b (1 mg)
was subjected to acidic methanolysis with 1 M HCl-MeOH.
The reaction mixture was kept for 12 h at 80 °C in a sealed

1530 Journal of Natural Products, 2005, Vol. 68, No. 10
Barbieri et al.
tube, then dried under nitrogen and partitioned between
CHCl3 and H2O-MeOH (8:2) to give an aqueous layer contain-
ing the methylmannoside and the inositol (fraction A) and an
organic layer containing the fatty acyl methyl esters (fraction
B). After removal of the solvent, fraction B was analyzed by
GC-MS and its components were identified as methyl octade-
canoate (tR ) 22.88 min, 33%), methyl 10-methyloctadecanoate
(tR ) 23.66 min, 51%), and methyl 12-methyloctadecanoate (tR
) 23.71 min, 16%).
Methyl 2,3,4,6-tetra-O-benzoyl-r-D-mannopyranoside.
D-Mannose (2.0 mg) was subjected to acidic methanolysis, and
the resulting methyl glycosides were benzoylated with benzoyl
chloride (20 µL) in pyridine (200 µL) at 25 °C for 16 h. The
reaction was then quenched with MeOH and after 30 min was
dried under nitrogen. Methyl benzoate was removed by keep-
ing the residue under vacuum for 24 h with an oil pump. The
residue was purified by HPLC (column: Luna SiO2, 5 µm, 4
× 250 mm, eluent: n-hexane-i-PrOH, 99:1, flow: 1 mL/min),
affording methyl 2,3,4,6-tetra-O-benzoyl-R-D-mannopyranoside
(tR ) 9.5 min): 1H NMR (CDCl3) δ 8.10 (2H, d, J ) 7.8 Hz,
benzoyl ortho protons), 8.06 (2H, d, J ) 7.8 Hz, benzoyl ortho
protons), 7.95 (2H, d, J ) 7.8 Hz, benzoyl ortho protons), 7.84
(2H, d, J ) 7.8 Hz, benzoyl ortho protons), 7.61-7.23 (12H,
overlapping signals, benzoyl protons), 6.11 (1H, t, J ) 10.1
Hz, H-4), 5.91 (1H, dd, J ) 10.1 and 3.3 Hz, H-3), 5.70 (1H,
dd, J ) 3.3 and 1.7 Hz, H-2), 5.01 (1H, d, J ) 1.7 Hz, H-1),
4.71 (1H, dd, J ) 12.1 and 2.6 Hz, H-6a), 4.50 (1H, dd, J )
12.1 and 4.5 Hz, H-6b), 4.42 (1H, ddd, J ) 10.1, 4.5, and 2.6
Hz, H-5), 3.55 (3H, s, OMe); CD (MeCN) λmax ) 240 nm (∆ꢀ )
-31), 223 nm (∆ꢀ ) +15).
Acknowledgment. The authors are very grateful to Prof.
J. R. Pawlik, UNCW, for inviting them to participate in the
third “Pawlik Expedition” under the NSF project grant entitled
“Assessing the Chemical Defenses of Caribbean Invertebrates”,
during which the material was collected, and to Prof. M.
Pansini, University of Genova, for the sponge taxonomy
determination. Mass and NMR spectra were recorded at the
“Centro di Servizi Interdipartimentale di Analisi Strumentale”,
Universita` di Napoli “Federico II”. The assistance of the staff
is gratefully acknowledged. This research project is funded by
the Italian Government, MIUR PRIN (Italy).
Supporting Information Available: 1D and 2D NMR spectra
of discoside peracetate (2b) in CDCl3 and C6D6; 1H NMR and CD
spectra of methyl 2,3,4,6-tetra-O-benzoyl-R-D-mannoside. This material
is available free of charge via the Internet at http://pubs.acs.org.
References and Notes
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Absolute Configuration Determination. Fraction A from
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(12) Piel, J.; Hui, D.; Wen, G.; Butzke, D.; Platzer, M.; Fusetani, N.;
Matsunaga, S. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 16222-16227.
1
and its H NMR and CD spectra with those of the synthetic
glycosides prepared from D-mannose.
NP050241Q