J. Nat. Prod. 1999, 62, 51-53
51
Tsugicoline E, a New Polyoxygenated Protoilludane Sesquiterpene from the
Fungus Laurilia tsugicola1
Alberto Arnone,‡ Cristiana De Gregorio,‡ Stefano Valdo Meille,† Gianluca Nasini,*,‡ and Giancarlo Sidoti†
Centro del CNR per le Sostanze Organiche Naturali, Dipartimento di Chimica, Politecnico di Milano, via Mancinelli 7,
I 20131 Milano, Italy
Received March 30, 1998
Tsugicoline E (3) has been isolated from cultures of the Basidiomycetous fungus Laurilia tsugicola and
its structure deduced from 1H and 13C NMR and single-crystal X-ray diffraction studies. The suggested
absolute configuration is consistent with biogenetic considerations.
In the course of a screening program for biologically
active novel metabolites from Basidiomycetous fungi, we
found that still liquid cultures of the mushroom Laurilia
tsugicola (Echinodontiaceae) are a rich source of new
sesquiterpenes having the protoilludane skeleton, such as
tsugicolines A (1) -D.2 Compound 1 was successively
converted via chemical reactions into the corresponding
sterpurane derivative 2.3 In this paper we describe the
isolation of a related compound, tsugicoline E (3), and
present its structure elucidation using mass spectrometry,
NMR spectroscopy, and single-crystal X-ray diffraction.
Table 1. 1H NMR Data for Compound 3 in (CD3)2SO
Results and Discussion
Tsugicoline E (3) was isolated as white crystals, mp 219221 °C, [R]D -38° (c 0.1, MeOH). Elemental analysis and
FABMS (MH+, 285) established C15H24O5 as the molecular
formula, indicating the presence in 3 of a molecule of water
more than compound 1. Strong peaks observed in the mass
spectrum at m/z 267, 249, and 231 were assumed due to
sequential loss of three molecules of water.
A comparison of the 13C and 1H NMR data of compounds
1 and 3 (Table 1 and Experimental Section)2 suggested that
the two metabolites share the same basic protoilludane
skeleton, the only relevant differences being the carbons
of the R,β-unsaturated ketone moiety. In fact, the sp2
carbons resonating at δ 153.0, 144.0, and 200.1 (C-2, C-4,
and C-5) in 1 were replaced by sp3 carbons resonating at δ
80.3, 55.6, and 107.8. The lack of vicinal coupling between
the new CH proton and H2-1 indicates that it must be
placed at C-4, while the chemical shift values exhibited by
C-2 and C-5 are in agreement with alcoholic and hemiketal
carbons. Formation of the tetraacetyl derivative 4 confirmed the presence of four hydroxy groups. NOE enhancement observed for H-4 (12%), by irradiation of H3-8, and
those observed for H-6 (3%) and H-9 and -13 (2%), by
irradiation of Hβ-1 at δ 3.78, permitted us to assign the
stereochemistry as 2R,4R,5S.
A possible scheme of formation of 3 in vivo could involve
a Michael addition of water onto the unsaturated ketone
system of 1, followed by intramolecular acetalization.
Although the polycyclic structure of 3 may appear rather
cumbered, the preference for this structure over the corresponding open form 5 is apparent from molecular modeling. In fact, structure 3 is the more stable according to
* To whom correspondence should be addressed. Tel.: +39 2 23993046.
Fax: +39 2 23993080. E-mail: vajna@dept.chem.polimi.it.
† Dipartimento di Chimica.
‡
Centro del CNR per le Sostanze Organiche Naturali, associated with
the National Institute for the Chemistry of Biological Systems-Italy.
10.1021/np980124d CCC: $18.00
b
protona
δH
1Rb
1β
3
4
6
8
9
10R
10β
12R
12β
13
14
15
3.66 d
3.78 d
3.38 d
1.73 s
3.92 s
0.87 s
1.99 m
1.24 dd
1.33 dd
1.79 dd
1.46 dd
1.96 m
1.08 s
0.97 s
J(H,H)/Hz
11.0
11.0
11.2
13.0, 6.6, 6.5
13.0, 12.5
12.5, 6.6
13.8, < 0.5
13.8, 7.2
11.2, 7.2, 6.5, < 0.5
a The hydroxy protons resonated at δ 6.49, 4.80, 4.75, and 4.68.
Numbering system is that used for the protoilludane skeleton.
calculations performed with the molecular mechanics
program DISCOVER (about 29 kcal/ mole) or with MOPAC
(about 24 kcal/ mole). A signal at δ 107.3 in the 13C NMR
spectrum of tetraacetate 4, attributable to the C-5 ketal
carbon, indicates that 3 retains the closed structure even
after acetylation.
A view of 3 showing its relative configuration
(2R,3S,4R,5S,6S,7R,9S,13R) and numbering scheme is
shown in Figure 1. The structure of 3 is, to our knowledge,
the first presenting a cyclobutane ring fused to both a
cyclohexane and a furanoid ring. Each of these three rings
is fused cis to both the other two, and, in addition, there is
a cyclopentane ring also cis-fused only to the cyclohexane
ring. Bond lengths and angles in 3 are normal; the O(5)C(5) bond distance [1.373(5) Å] is somewhat short com-
© 1999 American Chemical Society and American Society of Pharmacognosy
Published on Web 11/21/1998
52 Journal of Natural Products, 1999, Vol. 62, No. 1
Figure 1. Crystalline conformation of 3 showing its probable absolute
configuration.
pared to standard hemiacetal bond distances (1.401 Å)4
because of the increased s-character in the exocyclic bonding orbitals. The cyclobutane ring shows an intermediate
puckering (q ) -0.202 Å); the average values of ring bond
lengths (1.553 Å), bond angles (89.1°), and ring torsion
angles (14.8°) are in agreement with literature values5 for
cyclobutane rings with similar puckering. Rather than a
twisted conformation, the furanoid ring adopts an envelope
conformation, with the oxygen in the apical position,
consistent with a φ2 value6 of 348°. The cyclohexane ring
is found in a distorted conformation, intermediate between
a chair and a half-chair, while the cyclopentane, fused only
to the six-membered ring, displays a φ2 value (168°) quite
typical of an envelope conformation with C(9) in the apical
position.6 The crystal structure shows a weak intramolecular hydrogen bond that results in a five-atom ring formed
by the hydrogen on O(6) and O(5) as acceptor [O(5)‚‚‚H(O6)
2.217 Å; O(5)‚‚‚H(O6) 2.703 Å; O(5)‚‚‚H(O6)sO(6) 129°]
(Figure 1). A 2D network orthogonal to c of strong intermolecular hydrogen bonds involves the hydrogens on the
O(5) and O(3) hydroxyls with O(2) and the hemiacetal
oxygen O(1), respectively.
Work is in progress to study the compounds obtained
from the reaction of compound 1 in the presence of
nucleophiles.7 Tsugicoline E (3) is inactive against Bacillus
cereus, Bacillus subtilis, and Saccharomyces cerevisiae at
a concentration of 100 µg on disks.
Experimental Section
General Experimental Procedures. Melting points were
determined on a Kofler apparatus and are uncorrected; optical
rotations were obtained on a JASCO DIP-181 polarimeter; MS
were obtained with a Finnigan-MAT TSQ70 spectrometer.
NMR spectra were acquired on a Bruker AC 250L spectrometer operating at 250.1 MHz for 1H and 62.9 MHz for 13C. TLC
and PLC were performed with Merck HF254 Si gel. Owing to
the complexity of the purification procedure, we report the Rf
value on RP-18 plates in Me2CO-H2O (2:1).
Molecular modeling calculations were performed using the
program INSIGHT II, 2.3.5 (Biosym Technologies, San Diego,
CA) and with MOPAC 6.00 included in the same program.
Organism. A strain of Laurilia tsugicola (CBS 248.51)
received from Centraal Bureau voor Schimmel Cultures,
Baarn, was cultured as described previously2 in (40) Erlenmeyer flasks (250 mL).
Isolation and Purification of 3. EtOAc extracts of the
cultures of L. tsugicola were chromatographed on a column of
flash Si gel with a gradient of CH2Cl2-MeOH as eluent; after
the elution of tsugicolines A-D2 compound 3 (15 mg) was
eluted with a ratio (7:1), and the fractions collected and
evaporated were crystallized from Me2CO.
Tsugicoline (3): Rf 0.7; IR (KBr) νmax 3300 (OH), 2954,
2929, 1452, 1286, and 1182 cm-1; anal. C 63.3%, H 8.4%, calcd
Arnone et al.
for C15H24O5, C 63.36%, H 8.51%; CIMS m/z 267 (MH+ - 18);
FABMS m/z 285 (MH+, 7%), 267 (100), 249 (20), 231 (12), 191
(14), 173 (12); 1H NMR spectroscopic data reported in Table
1; selected NOE experiments [(CD3)2SO] {HR-1} enhanced
Hβ-1 (13%), H-4 (1%); {Hβ-1} enhanced HR-1 (13%), H-6 (3%),
H-9 and -13 (2%); {H-6} enhanced Hβ-1 (4%), H-9 and -13 (4%);
{H3-8} enhanced H-4 (12%), HR-10 (2.%), Hβ-10 (3%); {H-9
and -13} enhanced Hβ-1 (3%), H-6 (6%), H3-8 (0.5%), Hβ-10
(3%) Hβ-12 (3.5%), H3-15 (1%); {H3-14} enhanced H-3 (3.5%),
HR-10 (2.5%), HR-12 (4.5%); {H3-15} enhanced H-9 and -13
(2.5%), Hβ-10 (3.5%), Hβ-12 (4.5%); 13C NMR [(CD3)2SO] δ
107.5 (s, C-5), 80.3 (s, C-2), 73.7 and 73.4 (d, 1J ) 140 and 142
Hz, C-3 and -6), 72.9 (t, 1J ) 146 Hz, C-1), 55.6 (d, 1J ) 146
Hz, C-4), 46.0 and 42.8 (d, 1J ) 128 Hz, C-9 and -13), 43.1 and
43.0 (t, 1J ) 128 Hz, C-10 and -12), 35.5 and 35.4 (s, C-7 and
-11), 32.5 and 32.4 (q, 1J ) 125 Hz, C-14 and -15), and 19.2 (q,
1J ) 127 Hz, C-8).
Acetylation of 3. Compound 3 (25 mg) was dissolved in
dry pyridine (0.4 mL), Ac2O was added (0.8 mL), and the
solution was kept at 0 °C for 2 days. The mixture was then
poured into ice-water and extracted with CH2Cl2. Evaporation
of the extract followed by PLC in hexane-EtOAc (1:1) of the
residue gave tetraacetate 4 as a solid (20 mg): mp 123-125
°C; [R]D -17° (c 0.07, MeOH); FABMS m/z 453 [MH+] (10%),
393 [MH+ - 60] (24), 351 (18), 307 (20), 291 (22), 273 (43),
231 (63), 215 (100); CIMS m/z, 393; 1H NMR (CDCl3) δ 5.72
(1H, br d, J ) 11.3 Hz, H-3), 5.09 (1H, br s, H-6), 4.55 and
4.16 (2H, d, J ) 10.8 Hz, H2-1), 3.09 (1H, br s, H-4), 2.38 and
2.36 (2H, m, H-9 and -13), 2.12, 2.09, 2.08, and 2.00 (12H, s,
4 × OAc), 1.74, 1.55, 1.51, and 1.38 (4H, m, H2-10 and -12),
1.11, 1.09, and 1.01 (9H, s, H3-8, -14, and -15); 13C NMR
(CDCl3) δ 170.8, 170.7, 169.7, and 168.6 (s, MeCO2), 107.3 (s,
C-5), 87.1 (s, C-2), 77.4 and 70.7 (d, C-3 and -6), 75.8 (t, C-1)
54.6 (d, C-4), 46.9 and 40.7 (d, C-9 and -13), 42.9 and 42.5 (t,
C-10 and -13), 37.5 and 35.3 (s, C-7 and -11), 32.6, 32.2, 21.8,
21.3, 21.1, 20.8, and 19.8 (q, Me).
Crystal Data and X-ray Crystal Structure Determination of Tsugicoline E (3). Crystals of 3, suitable for X-ray
analysis, were obtained by crystallization from Me2CO.
Crystal data: C15H24O5; M ) 284.34: Orthorombic, a )
6.014(1), b ) 9.810(1), c ) 24.330(2) Å, V ) 1435.4(3) Å3, space
group P212121, Z ) 4, Dx ) 1.316 Mg m-3, µ ) 0.804 mm-1,
F(000) ) 616; colorless prismatic crystals, dimension 0.1 × 0.2
× 0.5 mm3.
Data Collection. Siemens P4 diffractometer, θ-2θ scan
technique, graphite-monochromated Cu KR radiation; 2338
reflections measured (3.63 < θ < 56.91°, +h, +k, +l and -h,
-k, -l), 1946 unique. Three standard reflections measured
every 100 reflections showed no significant decay. Data were
corrected for Lorentz and polarization effects. An empirical
absorption correction was also applied.
Structure Analysis and Refinement. The crystal structure was solved by direct methods (SIR 92)8 and refined by
full-matrix least squares on F2 values (SHELXL-93).9 Nonhydrogen atoms were refined with anisotropic temperature
factors. Hydrogen atoms were included at calculated positions
and refined in the riding mode. Final values of the residuals
R and wR2 [for 1701 reflections with I > 4σ(I)] were,
respectively, 0.0596 and 0.1649. The highest and the lowest
peaks in final difference Fourier map were 0.186 and -0.272e
Å-3. The refined value of Flack’s x parameter10 0.0(5), and its
standard deviation, suggested the absolute configuration as
(2R,3S,4R,5S,6S,7R,9S,13R) consistent by biogenetic reason.11
Acknowledgment. Thanks are due to Dr. Gabriella
Morini (Disma, Universita′ di Milano) for the molecular
modeling calculations.
References and Notes
(1) Secondary Mould Metabolites Part 55. For Part 54, see Arnone, A.;
Nasini, G.; Vajna de Pava, O. Phytochemistry 1997, 46, 1099-1101.
(2) Arnone, A.; Brambilla, U.; Nasini, G.; Vajna de Pava, O. Tetrahedron
1995, 51, 13357-13364.
Tsugicoline E from Laurilia tsugicola
(3) Arnone, A.; De Gregorio, C.; Nasini, G.; Vajna de Pava, O. J. Chem.
Soc., Perkin Trans. 1 1997, 1523-1525.
(4) International Tables for Crystallography, Vol. C, Wilson A. J., Ed.,
Kluwer Academic: Dordrecht, 1992.
(5) Allen, F. H. Acta Crystallogr. 1984, B40, 64-72.
(6) Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97, 1354-1358.
(7) Arnone, A.; De Gregorio, C.; Nasini, G.; Vajna de Pava, O. Manuscript
in preparation.
(8) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1993, 26, 343-350.
Journal of Natural Products, 1999, Vol. 62, No. 1 53
(9) Sheldrick, G. M SHELXL93 Program for Crystal Structure Refinement, University of Göttingen, Germany, 1993.
(10) Flack, H. D. Acta Cryst. 1983, A39, 876-881.
(11) Crystallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre. Copies of the data can be obtained free
of charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK.
NP980124D