HMBC data provided evidence for the nature of the
linkages between the four monosaccharides. Correlations
between the 6-deoxytalose anomeric proton resonance at δ
4.77 and the Glu2 C-6 resonance at δ 69.4 demonstrated
that there was a 1,6-glycosidic linkage between the 6-deoxy-
talose and Glu2 residues. A strong HMBC correlation
between the Glu2 H-2 resonance at δ 3.97 and the Qui
anomeric carbon resonance at δ 96.2 established a 1,2
glycosidic bond between Qui and Glu2. Finally, a correlation
between the Glu1 H-2 resonance at δ 4.21 and an anomeric
resonance at δ 100.1 (Glu2-C-1) showed there was a 1,2-
glycosidic link between Glu2 and Glu1. As described above,
coupling constant data showed that glucose-1 and glucose-2
had â anomeric configurations and that quinovose had an R
anomeric configuration. ROESY data showed that the
6-deoxytalose residue had the â anomeric configuration.
Comparison of the ESMS of the underivatized natural
product mixture of caminosides, differing only in the aglycon
fragment, injected in MeOH ([M + Na]+ m/z 1049) and
MeOD ([M + Na]+ m/z 1058) showed that there were only
9 exchangeable protons, even though the identified tetra-
saccharide fragment had 11 available hydroxyls. In addition,
the NMR data for the underivatized natural product mixture
contained resonances that could be assigned to acetyl (δ 1H
Sponges are emerging as a rich source of novel biologi-
cally active glycolipids.6 Caminoside A (1) has several
structural features not found in sponge glycolipids reported
to date. It has a fully substituted glucose residue (Glu-2)
embedded in the middle of the molecule, it contains a
6-deoxytalose residue, which is rare in nature, and the methyl
ketone functionality in the lipid aglycon is without precedent
in sponge metabolites.
Caminoside A (1) is the first natural product known to be
active (IC50 ) 20 µM) in a new bioassay designed to screen
for type III secretion inhibitors that potentially represent
novel agents to control pathogenic E. coli by thwarting their
pathogenicity without actually killing the bacteria.4d The full
significance of the biological activity displayed by camino-
side A (1) in the new assay is currently under investigation
in our laboratories. The type III secretion inhibitor screen
was designed to select for compounds that did not display
conventional antimicrobial activity against E. coli. To
confirm that this was indeed the case for caminoside A (1),
it was screened for traditional antimicrobial activity against
a panel of human and plant pathogens. Caminoside A (1)
showed reasonably potent in vitro inhibition of methicillin
resistant Staphylococcus aureus (MIC: 12 µg/mL) and
vancomycin resistant Enterococcus (MIC: 12 µg/mL). As
expected, it did not inhibit the growth of gram negative
pathogenic E. coli (MIC: >100 µg/mL).
1
1.96, s, 3H and 13C 20.4, 169.2) and butyryl (δ H 0.83, t,
3H; 1.47, m, 2H; 2.29, dt, 1H, 2.17, dt, 1H dt and 13C 13.3,
17.7, 35.4, 172.0) residues, respectively. Therefore, cami-
noside A (1) had to already contain an acetate and a butyrate
ester before derivatization with acetic anhydride to give the
peracetate 2.
Acknowledgment. Financial support was provided by the
NSERC (R.J.A.), CIHR (A.G., B.B.F.), and the Canadian
Bacterial Disease Network Center of Excellence (B.B.F.).
The authors thank M. LeBlanc and D. Williams for assisting
with the sponge collection and the Canadian National High
Field NMR Centre (NANUC) for their assistance and use
of the facilities. NANUC is funded by CIHR, NSERC, and
the University of Alberta.
With the structure of the tetrasaccharide fragment of
caminoside A in hand from analysis of the NMR data for
1
the peracetate 2, it was possible to go back and assign H
and 13C NMR resonances to the sugar portion of caminoside
A (1) using the data for the mixture of natural products that
differed only in the aglycon. Using these assignments for
the underivatized compound, HMBC correlations were
observed between the Glu2 H-4 resonance at δ 4.57 and the
acetyl carbonyl resonance at δ 169.2 (Glu2-C-11), and
between the Glu2 H-3 resonance at δ 5.16 and the butyryl
carbonyl resonance at δ 172.0 (Glu2-C-7). This placed the
butyrate ester at C-3 of Glu2 and the acetate ester at C-4 of
Glu2, completing the structure of caminoside A and its
peracetate as shown in 1 and 2, respectively (Figure 1). The
lack of dispersion in the methylene proton resonances near
the C-10 region of the aglycon made it impossible to use
Mosher-type methodology to determine the absolute con-
figuration at C-10.
Supporting Information Available: Tables of NMR
data, 1D and 2D NMR spectra for caminoside A (1) and the
peracetate (2), and experimental procedures. This material
OL0268337
(6) (a) Costantino, V.; Fattorusso, E.; Mangoni, A. In BioactiVe
Compounds from Natural Sources; Tringali, C., Ed.; Taylor and Francis:
New York, 2001; Chapter 14, p 556. (b) Costantino, V.; Fattorusso, E.;
Imperatore, C.; Mangoni, A. Eur. J. Chem. 2001, 4457. (c) Sata, N.; Asai,
N.; Matsunaga, S.; Fusetani, N. Tetrahedron 1994, 50, 1105.
4092
Org. Lett., Vol. 4, No. 23, 2002