Synthesis and Biological Activity of Enantiomers of Antitumor Irofulven

Article abstract of DOI:10.1021/jo035084j

Stereoselective synthesis of (-)-irofulven has been achieved by cycloaddition of (R)-5-chloro-5-methyl-2-cyclopentenone to the 1,3-dipolar intermediate from 1-acetyl-1-(diazoacetyl)cyclopropane. The enantiomer, (+)-irofulven, was prepared in a similar way starting with (S)-5-chloro-5-methyl-2-cyclopentenone. (+)-Irofulven was 5 to 6 times less toxic than (-)-irofulven to adenocarcinoma (MV 522) cells.

Full text of DOI:10.1021/jo035084j

Syn th esis a n d Biologica l Activity of En a n tiom er s of An titu m or
Ir ofu lven
Trevor C. McMorris,*,† Michael D. Staake,† and Michael J . Kelner‡
Department of Chemistry and Biochemistry, University of California, San Diego,
La J olla, California 92093-0506, and Department of Pathology, UCSD Medical Center,
San Diego, California 92103-8320
tmcmorris@ucsd.edu
Received J uly 25, 2003
Stereoselective synthesis of (-)-irofulven has been achieved by cycloaddition of (R)-5-chloro-5-methyl-
2-cyclopentenone to the 1,3-dipolar intermediate from 1-acetyl-1-(diazoacetyl)cyclopropane. The
enantiomer, (+)-irofulven, was prepared in a similar way starting with (S)-5-chloro-5-methyl-2-
cyclopentenone. (+)-Irofulven was 5 to 6 times less toxic than (-)-irofulven to adenocarcinoma (MV
522) cells.
In tr od u ction
The toxic mushroom Omphalotus illudens (formerly
Clitocybe illudens) is the source of highly toxic sesquit-
erpenes illudin S and M (1, 2).1 The compounds were
tested many years ago by the National Cancer Institute
and were found to possess antitumor activity but with a
poor therapeutic index. However, certain derivatives of
these compounds have greatly improved efficacy as
antitumor agents. In particular, the derivative irofulven
(hydroxymethylacylfulvene, 4)2 has been extensively
investigated and is currently in phase II clinical trials
against ovarian, prostate, and gastrointestinal cancers,
both as a monotherapy3 and in combination with well-
known anticancer drugs.
F IGURE 1. Structures of illudins and derivatives.
SCHEME 1. Retr oa n a lysis of th e Ir ofu lven Tota l
Syn th esis
Irofulven is best prepared by semisynthesis from
illudin S, which is readily obtained from fermentation of
O. illudens. Treatment with dilute H2SO4 converts 1 to
acylfulvene 3 in a reverse Prins reaction. Reaction of 3
with formaldehyde in dilute H2SO4 gives irofulven in a
yield of 40% from 1.
The total synthesis of (()-acylfulvene has been achieved
by means of the Padwa carbonyl ylide 1,3-dipolar cy-
cloaddition methodology.4 More recently a synthetic
approach to either enantiomer of acylfulvene, utilizing
the allenic Pauson-Khand reaction, has been reported
by Brummond et al.5 We now disclose an alternative
synthesis that was designed to furnish either enantiomer
of irofulven. The retrosynthesis is outlined in Scheme 1.
We planned to establish the chirality in the first step by
using 5-chloro-5-methyl-2-cyclopentenone (5) of known
absolute configuration. Cycloaddition of 5 with the
dipolar intermediate from diazoketone (6) would give a
product whose absolute configuration could be deduced.
† University of California.
‡ UCSD Medical Center.
(1) McMorris, T. C.; Anchel, M. J . Am. Chem. Soc. 1963, 85, 831.
(2) McMorris, T. C.; Kelner, M. J .; Wang, W.; Yu, J .; Estes, L. A.;
Taetle, R. J . Nat. Prod. 1996, 59, 896.
(3) Von Hoff, D. D.; Cox, J ohn, V.; Eder, J . P.; Tempero, M. A.;
Eckhardt, G.; Rowinsky, E. K.; Smith, S. L.; Stuart, K. E.; Proper, J .;
Campbell, E. R.; MacDonald, J . R. Activity of Irofulven (MGI 114) in
Patients With Advanced Pancreatic Cancer Refractory to Gemcitabine.
In Proceedings AACR-NCI-EORTC International Conference, Nov
7-10, 2000, Amsterdam; American Association for Cancer Research,
Inc.: Philadelphia, PA, 2000; Abstract No. 365.
(4) McMorris, T. C.; Hu, Y.; Yu, J .; Kelner, M. J . Chem. Commun.
1997, 315.
Assuming the stereochemistry of the oxygen bridge to
be thus established we believed it would be possible to
control formation of the chiral center of irofulven. That
center would be constructed by a Grignard reaction.
Having served its purpose the chloro substituent would
be removed by dehydrohalogenation, thus setting the
stage for creating the fulvene structure.
(5) Brummond, K. M.; Lu, J .; Petersen, J . J . Am. Chem. Soc. 2000,
122, 4915.
10.1021/jo035084j CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/06/2003
J . Org. Chem. 2004, 69, 619-623
619

McMorris et al.
SCHEME 2 a
a
Reagents and conditions: (a) cat. Rh2(OAc)4, CH2Cl2, reflux,
1 h (54% 7, 20% 8); (b) K2CO3, 90% i-PrOH/H2O, rt, 6 h (70%); (c)
Ac2O, Py, rt, 2 h (90%); (d) MeMgCl, THF, -78 °C, 2 h, then 0 °C,
2 h (87%).
F IGURE 2. X-ray structure of compound 12.
Syn th esis
SCHEME 3 a
Racemic 5-chloro-5-methyl-2-cyclopentenone (()-5 was
readily prepared according to the literature procedure.6
Resolution of the enantiomers was achieved by asym-
metric reduction of (()-5 with BH3‚THF and catalytic (S)-
2-methyl-CBS-oxazaborolidine. This furnished a diaster-
eomeric mixture of the (R)-cyclopentenols which were
readily separated and reoxidized to give (+)-5 (98% ee)
and (-)-5 (82% ee). Likewise, reduction of (()-5 with
catalytic (R)-2-methyl-CBS-oxazaborolidine afforded di-
astereomeric (S)-cyclopentenols which after separation
and reoxidation gave (-)-5 (98% ee) and (+)-5 (83% ee).7
Cycloaddition reaction of cyclopentenone (+)-5 with
diazoketone 6 and a catalytic amount of Rh2(OAc)4 in
refluxing CH2Cl2 yielded a mixture of diastereomers 7
and 8 (54% and 20%, respectively, Scheme 2). The exo
products were the only ones isolated. X-ray crystal-
lographic analysis established the relative configuration
of the chiral centers depicted in 7.8
The oxo bridge in diastereomer 7 was cleaved under
mild basic conditions (K2CO3, 2-propanol-H2O 9:1; the
best yields were obtained with this solvent system).
Acetylation of alcohol 9 to give 10 followed by Grignard
reaction with methylmagnesium chloride at low temper-
ature gave a high yield (87%) of a single cis glycol 11
with the indicated stereochemistry (Scheme 2). This
structure was confirmed by forming crystalline acetonide
12 (83%, Scheme 3) whose absolute configuration was
firmly established by X-ray crystallographic analysis
(Figure 2). Noteworthy features of the Grignard reaction
were (a) complete regioselectivity (the cyclopentenone
was unreactive) and (b) complete stereoselectivity: only
one tertiary alcohol was obtained, indicating the directive
influence of the adjacent R-acetoxy group.9 Thus the
stereochemistry at the new chiral center was firmly
established.
a
Reagents and conditions: (e) 2,2-dimethoxypropane, cat. p-
TsOH, DMF, rt, 24 h (83%); (f) DBU, benzene, rt, 1.5 h; (g) cat.
RhCl3‚3H2O, EtOH, reflux, 20 min (62%, 2 steps); (h) 80% AcOH/
H2O, 90 °C, 2 h (78%); (i) DIBALH, CH2Cl2, -78 °C, 30 min (49%);
(j) IBX, DMSO, rt, 2 h (53%).
Dehydrohalogenation of intermediate 12 was achieved
by treatment with DBU in benzene.10 A mixture of
exocyclic and endocyclic enones 13 and 14 was formed
in a 13:1 ratio. Without separation, the mixture was
refluxed in EtOH with rhodium chloride,11 which caused
isomerization of the exocyclic to the more stable endocy-
clic isomer with overall yield of 62%.
Removal of the acetonide protecting group gave glycol
15, which on DIBALH reduction of the ketone and
concomitant 1,4-elimination of the resulting hydroxy
group yielded fulvene 16 in 49% yield. On oxidation with
o-iodoxybenzoic acid (IBX) 16 gave (-)-acylfulvene 3,
which was identical with the compound derived from
illudin S in all respects including optical rotation.12
Starting from cyclopentenone (-)-5 and employing the
same set of reactions, the enantiomer of acylfulvene (+)-3
was prepared in 10 steps in an overall yield of 3.1%. The
(6) Rizzo, C. J .; Dujlap, N. K.; Smith, A. B., III J . Org. Chem. 1987,
52, 5280.
(7) McMorris, T. C.; Staake, M. D. J . Org. Chem. 2002, 67, 7902.
(8) Relative configuration was established by analysis of the race-
mate corresponding to 7, which was obtained in an earlier experiment
from the cycloaddition of diazoketone 6 with (()-5.
(9) Reaction of unprotected 9 with MeMgCl under similar conditions
gives the stereoisomeric trans diol in low yield (30%). Cis diol 11 was
not detected.
(10) J ean-Baptiste, W.; Francois, R. Bull. Soc. Chim. Fr. 1979, 5-6,
II-273.
(11) Dasanayaki, B. W.; Weedon, A. C. Synthesis 1983, 952.
620 J . Org. Chem., Vol. 69, No. 3, 2004

Synthesis of Enantiomers of Antitumor Irofulven
SCHEME 4. Mech a n ism of Biologica l Action of Ir ofu lven
TABLE 1. Com p a r ison of Toxicity of (-)-Acylfu lven e
w ith (+)-Acylfu lven e a n d (-)-Ir ofu lven w ith (+)-Ir ofu lven
in MV 522 Ad en oca r cin om a Cellsa
appear to be more likely since the activated intermediate
is so unstable. One might thus conclude that the stere-
ochemistry of the tertiary hydroxyl does play a role in
the enzyme-catalyzed activation step.
2 h
48 h
It is interesting to note that an NADPH-dependent
alkenone oxidoreductase (AOR) enzyme has been re-
ported to reduce the R,â-unsaturated ketone of iroful-
ven.16 This follows our earlier report of a similar reduc-
tion by a cytosolic NADPH enzyme.13 Human embryonic
kidney cells that overexpress AOR are 20-fold more
sensitive to irofulven-induced cytotoxicity than control
cells.16
(-)-acylfulvene
(+)-acylfulvene
(-)-irofulven
(+)-irofulven
300 ( 50
1700 ( 600
200 ( 20
350 ( 20
1900 ( 300
170 ( 20
1300 ( 400
900 ( 200
a
IC50 values (nM) after 2 h and 48 h exposure to compounds.
IC50 is the concentration of the fulvene at which 50% inhibition
occurred in the Trypan blue assay (48 h) or 50% inhibition of
thymidine incorporation into cellular DNA (in the 2 h assay).
acylfulvene enantiomers were converted to the corre-
sponding (-)-irofulven and (+)-irofulven via the known
method.2
Exp er im en ta l Section
Com p ou n d 7. A solution of 617 (550 mg, 4.21 mmol) in CH2-
Cl2 (12 mL) was added dropwise over a period of 40 min to a
refluxing solution of (+)-57 (98% ee, 1.31 g, 10.0 mmol),
rhodium(II) acetate (39 mg), and DMF (125 µL) in CH2Cl2 (12
mL). The solution was refluxed for an additional 20 min, then
concentrated and chromatographed (10:3 hexanes-ethyl ac-
etate) to give 452 mg of 7 (54%) and 167 mg of 8 (20%) as
white solids.
Biologica l Activity
The mechanism of action of irofulven is thought to
involve an activation step in which nucleophilic attack
on the R,â-unsaturated ketone by thiol or NADPH
(Scheme 4) leads to a highly reactive intermediate.13
Opening of the cyclopropane ring, accompanied by loss
of the tertiary hydroxyl, results in alkylation of protein
and DNA.14 It was of interest to determine if the
stereochemistry of the tertiary hydroxyl was critical to
the hypothesized activation step or to the alkylation step.
Therefore the toxicity of (+)-acylfulvene and (+)-irofulven
against a lung adenocarcinoma cell line MV522 was
compared to that of their (-)-enantiomers. The results
are shown in Table 1.
IC50 values were obtained for 2 and 48 h exposure
times. Previous studies have shown that sensitive cell
lines possess an energy-dependent transport mechanism
for taking up the drug. This results in toxicity at 2 h
being comparable to that after 48 h. In nonsensitive cells
toxicity at 2 h is less than that at 48 h.15
(+)-Acylfulvene was about 6 to 5 times less toxic than
(-)-acylfulvene after 2 or 48 h, respectively. Likewise,
(+)-irofulven was about 6 to 5 times less toxic than (-)-
irofulven after 2 or 48 h of exposure. Thus the (+)-
enantiomers do possess inherent toxicity, which, though
comparatively low, cannot be attributed to contamination
by the (-)-enantiomers. The difference in toxicity can
possibly be explained by differences in either the activa-
tion rate or the rate of the alkylation. The former would
Major diastereomer (7): [R]25D -85.0 (c 19.5 mg/mL, CHCl3);
1
mp 141-2 °C; H NMR (CDCl3) δ 0.72-0.78 (m, 1H), 1.03-
1.10 (m, 1H), 1.15-1.21 (m, 1H), 1.36-1.42 (m, 4H), 1.61 (s,
3H), 2.33 (dd, J ) 7.8, 13.8 Hz, 1H), 2.64 (dd, J ) 8.8, 14.0
Hz, 1H), 2.76 (d, J ) 8.4 Hz, 1H), 2.85 (q, J ) 8.1 Hz, 1H),
4.35 (s, 1H); 13C NMR (CDCl3) δ 12.2, 13.6, 15.0, 27.5, 38.5,
39.9, 42.1, 54.5, 69.1, 84.9, 88.2, 208.7, 211.2; IR (NaCl, thin
film) 3001, 2978, 1759, 1454 cm-1; MS (DEI) m/z (% rel
intensity) 256 (M+ + 2, 6), 254 (M+, 18), 225 (99), 197 (56),
124 (100), 43 (48); HRMS for C13H15ClO3 calcd 254.0710, found
254.0718. The relative configuration was confirmed by X-ray
crystallography.8
Minor diastereomer (8): [R]25 -121.3 (c 20.3 mg/mL,
D
CHCl3); mp 131-2 °C; 1H NMR (CDCl3) δ 0.74-0.80 (m, 1H),
1.02-1.09 (m, 1H), 1.17-1.23 (m, 1H), 1.34-1.40 (m, 4H), 1.63
(s, 3H), 1.93 (dd, J ) 8.6, 14.8 Hz, 1H), 2.71 (dd, J ) 7.8, 15.0
Hz, 1H), 3.00-3.12 (m, 2H), 4.28 (s, 1H); 13C NMR (CDCl3) δ
12.1, 13.6, 14.8, 22.7, 39.5, 39.6, 41.5, 54.1, 71.2, 83.9, 87.6,
206.0, 211.2; IR (NaCl, thin film) 2988, 1749, 1445 cm-1; MS
(DEI) m/z (% rel intensity) 256 (M+ + 2, 12), 254 (M+, 36), 225
(79), 191 (50), 124 (100), 43 (41); HRMS for C13H15ClO3 calcd
254.0710, found 254.0716.
Com p ou n d 9. To a solution of 7 (972 mg, 3.82 mmol) in
90% 2-propanol (250 mL) was added K2CO3 (3.75 g) at room
temperature. The mixture was stirred for 6 h then poured into
a mixture of ethyl acetate and water. The aqueous layer was
extracted with ethyl acetate and the combined organic layers
were washed with brine and dried with MgSO4. The solvent
(12) The optical rotation of the synthetic sample 3 compares with
that of a naturally derived authentic sample: [R]25 -494.2 (c 2.9 mg/
(16) Dick, R. A.; Yu, X.; Kensler, T. Characterization of the
Metabolism of the Investigational Anticancer Compound Irofulven and
Related Mycotoxins, Illudin S and M, by NADPH-Dependent Alkenal/
one Oxidoreductase from the Rat Liver; Proceedings of American
Association of Cancer Research, Annual Meeting, Vol. 44, 1st ed., 2003;
Abstract 2712.
D
mL, EtOH). This value differs from the value reported in ref 2.
(13) McMorris, T. C.; Elayadi, A. N.; Yu, J .; Hu, Y.; Kelner, M. J .
Drug Metab. Dispos. 1999, 27 (9), 983.
(14) Herzig, M. C.; Arnett, B.; MacDonald, J . R.; Woynarowski, J .
M. Biochem. Pharmacol. 1999, 58 (2), 217.
(15) Kelner, M. J .; McMorris, T. C.; Taetle, R. J . Natl. Cancer Inst.
1990, 82, 1562.
(17) Padwa, A.; Chinn, R. L.; Hornbuckle, S. F.; Zhang, Z. J . J . Org.
Chem. 1991, 56, 3271.
J . Org. Chem, Vol. 69, No. 3, 2004 621

McMorris et al.
was evaporated and the crude product chromatographed (10:3
HRMS for C17H24ClO3 (MH+) calcd 311.1414, found 311.1423.
The absolute configuration was confirmed by X-ray crystal-
lography.
hexanes-ethyl acetate) to give 681 mg of 9 (70%) as a white
solid: [R]25 -23.8 (c 10.4 mg/mL, ethyl acetate); mp 140-1
D
°C; 1H NMR (CDCl3) δ 1.25-1.34 (m, 1H), 1.40-1.50 (m, 1H),
1.65 (s, 3H), 1.71-1.80 (m, 1H), 1.92-2.00 (m, 1H), 2.06 (d, J
) 2.8 Hz, 3H), 2.38 (dd, J ) 7.2, 12.8 Hz, 1H), 2.48 (br, 1H),
2.66 (t, J ) 12.1 Hz, 1H), 3.09-3.21 (m, 1H), 4.03 (d, J ) 2.8
Hz, 1H); 13C NMR (CDCl3) δ 12.7, 19.7, 22.6, 26.9, 32.9, 37.7,
38.4, 70.9, 71.8, 123.7, 153.1, 198.1, 204.6; IR (NaCl, thin film)
3421, 2922, 1714, 1698, 1613, 1464 cm-1; MS (DEI) m/z (% rel
intensity) 256 (M+ + 2, 4), 254 (M+, 12), 218 (23), 161 (100),
91 (62), 77 (53); HRMS for C13H15ClO3 calcd 254.0710, found
254.0710; UV λmax (EtOH) 279 nm (ꢀ 11 130).
Com p ou n d 10. To a solution of 9 (450 mg, 1.52 mmol) in
acetic anhydride (15 mL) was added 0.6 mL of pyridine at room
temperature. The solution was stirred for 2 h then poured into
water. NaHCO3 was then added until bubbling ceased. The
aqueous layer was extracted with ethyl acetate and the
combined organic layers were washed with saturated NaHCO3
solution and brine. The solution was dried with MgSO4 and
concentrated. The crude product was chromatographed (10:3
Com p ou n d 14. To a solution of 12 (400 mg, 1.29 mmol) in
benzene (15 mL) was added DBU (400 µL, 2.67 mmol) at room
temperature. The mixture was stirred for 1.75 h, during which
time a white precipitate formed. The reaction was quenched
with acetic acid (0.5 mL) and the mixture added to water. The
aqueous layer was extracted with ether and the combined
organic layers were washed with water and brine. The solution
was dried with MgSO4 and concentrated to give 317 mg of 13
and 14 in a 13:1 ratio as a pale yellow liquid. Exocyclic double
bond isomer (13): 1H NMR (CDCl3) δ 0.37-0.43 (m, 1H), 0.90-
0.97 (m, 1H), 1.07-1.13 (s, 3H), 1.15 (s, 3H), 1.20 (s, 3H), 1.24-
1.33 (m, 1H), 1.34 (s, 3H), 2.14 (d, J ) 1.6 Hz, 3H), 2.75-2.86
(m, 3H), 4.23 (d, J ) 2.4 Hz, 1H), 5.33-5.37 (m, 1H), 6.00-
6.04 (m, 1H); 13C NMR (CDCl3) δ 7.9, 12.6, 14.4, 23.1, 27.2,
27.6, 28.0, 32.5, 36.3, 83.5, 85.2, 108.5, 116.9, 133.0, 147.5,
154.6, 193.2; IR (NaCl, thin film) 2984, 1694, 1623, 1433 cm-1
;
MS (20 eV) m/z (% rel intensity) 274 (M+, 29), 259 (14), 216
(60), 201 (100), 187 (28), 173 (58), 159 (26), 145 (24); HRMS
for C17H22O3 calcd 274.1569, found 274.1571.
hexanes-ethyl acetate) to give 473 mg of 10 (90%) as a white
The crude mixture of 13 and 14 was dissolved in 95%
ethanol (35 mL) to which RhCl3‚3H2O (30.5 mg, 0.116 mmol)
was added. The mixture was refluxed at 90 °C for 20 min then
diluted with ether. The solid was filtered off and the filtrate
concentrated. The crude product was chromatographed (5:1
hexanes-ethyl acetate) to give 213 mg of endocyclic double
bond isomer 14 (62%) as a pale yellow liquid, which solidified
1
solid: [R]25 -19.4 (c 14.6 mg/mL, CHCl3); mp 143-5 °C; H
D
NMR (CDCl3) δ 1.26-1.40 (m, 2H), 1.63 (s, 3H), 1.67-1.73 (m,
1H), 1.98-2.04 (m, 1H), 2.04 (d, J ) 2.8 Hz, 3H), 2.08 (s, 3H),
2.24 (t, J ) 12.0 Hz, 1H), 2.43 (dd, J ) 7.2, 12.8 Hz, 1H), 3.18-
3.26 (m, 1H), 5.19 (d, J ) 3.2 Hz, 1H); 13C NMR (CDCl3) δ
13.8, 20.1, 22.1, 23.6, 27.9, 35.0, 38.9, 39.9, 71.8, 72.9, 125.2,
154.5, 170.7, 198.7, 201.3; IR (NaCl, thin film) 2984, 1749,
1716, 1704, 1612, 1439 cm-1; MS (DEI) m/z (% rel intensity)
299 (MH+ + 2, 1), 297 (MH+, 3), 236 (20), 201 (100), 173 (21),
161 (37) 43 (73); HRMS for C15H18ClO4 (MH+) calcd 297.0893,
found 297.0881.
upon freezing: [R]25 +121.8 (c 10.7 mg/mL, CHCl3); mp 64-
D
1
66 °C; H NMR (CDCl3) δ 0.38-0.45 (m, 1H), 0.84-0.92 (m,
1H), 1.02-1.08 (m, 1H), 1.166 (s, 3H), 1.173 (s, 3H), 1.20-
1.26 (m, 1H), 1.34 (s, 3H), 1.87 (s, 3H), 2.10 (s, 3H), 3.22 (br s,
1H), 4.42 (d, J ) 2.8 Hz, 1H), 6.97 (s, 1H); 13C NMR (CDCl3)
δ 7.0, 11.3, 12.5, 14.0, 23.3, 27.1, 27.5, 31.6, 42.5, 83.0, 86.3,
109.3, 130.6, 145.9, 146.4, 148.4, 195.9; IR (NaCl, thin film)
2984, 2934, 2874, 1686, 1650, 1632, 1452, 1440 cm-1; MS (20
eV) m/z (% rel intensity) 274 (M+, 46), 259 (15), 216 (82), 201
(50), 173 (77), 159 (40), 146 (52), 109 (100); HRMS for C17H22O3
calcd 274.1569, found 274.1569.
Com p ou n d 11. To a solution of 10 (477 mg, 1.62 mmol) in
THF (40 mL) was added a solution of MeMgCl (3.0 M in THF,
2.25 mL, 6.75 mmol) at -78 °C. The solution was stirred for 2
h, warmed to 0 °C, stirred for an additional 2 h, and then
quenched with saturated NH4Cl solution. The aqueous layer
was extracted with ethyl acetate and the combined organic
layers were washed with brine and dried with MgSO4. The
solvent was evaporated and the crude product chromato-
graphed (2:1 hexanes-ethyl acetate) to give 377 mg of 11 (87%)
as a colorless gum: [δ]25D -19.2 (c 12.4 mg/mL, ethyl acetate);
1H NMR (CDCl3) δ 0.88-0.95 (m, 1H), 0.98-1.09 (m, 2H), 1.20
(s, 3H), 1.24-1.31 (m, 1H), 1.66 (s, 3H), 1.94 (d, J ) 2.0 Hz,
3H), 2.34-2.47 (m, 2H), 2.92-3.00 (m, 1H), 3.70 (d, J ) 3.6
Hz, 1H); 13C NMR (CDCl3) δ 6.4, 12.5, 13.1, 24.7, 26.7, 29.9,
38.6, 40.1, 70.5, 71.4, 73.4, 123.5, 156.2, 198.7; IR (NaCl, thin
film) 3528, 3397, 3009, 2975, 2927, 1706, 1604, 1439 cm-1; MS
(DEI) m/z (% rel intensity) 272 (M+ + 2, 2), 270 (M+, 5), 235
(22), 217 (25), 189 (28), 133 (30), 91 (32), 43 (100); HRMS for
Com p ou n d 15. A solution of 14 (127 mg, 0.541 mmol) in
80% acetic acid (45 mL) was heated at 90 °C for 2 h. The
solution was poured into saturated NaHCO3 solution and
extracted with ethyl acetate. The combined organic layers were
washed with water and brine then dried with MgSO4. The
crude product was chromatographed (1:1 hexanes-ethyl ac-
etate) to give 84 mg of 15 (78%) as a white solid: [R]25D -246.6
1
(c 9.7 mg/mL, ethyl acetate); mp 131-2 °C; H NMR (CDCl3)
δ 0.80-1.10 (m, 3H), 1.18-1.24 (m, 1H), 1.26 (s, 3H), 1.60 (br,
1H), 1.85 (s, 3H), 1.95 (s, 3H), 2.30 (br, 1H), 3.54 (br s, 1H),
3.94 (d, J ) 4.8 Hz, 1H), 7.08 (s, 1H); 13C NMR (CDCl3) δ 6.6,
11.2, 11.3, 11.7, 25.0, 29.9, 44.2, 71.5, 74.6, 126.4, 145.8, 147.1,
147.6, 195.0; IR (NaCl, thin film) 3439, 1666, 1632, 1612 cm-1
;
C
14H19ClO3 calcd 270.1023, found 270.1019.
MS (20 eV) m/z (% rel intensity) 234 (M+, 51), 216 (35), 201
(31), 173 (82), 159 (63), 145 (71), 43(100); HRMS for C14H18O3
calcd 234.1256, found 234.1257; UV λmax (EtOH) 286 nm (ꢀ
11 396).
Com p ou n d 12. To a solution of 11 (120 mg, 0.443 mmol)
and p-TsOH (20 mg) in DMF (3 mL) was added 2,2-dimethox-
ypropane (500 µL, 4.07 mmol) at room temperature. The
solution was stirred for 25 h, and then quenched with
saturated NaHCO3 solution. The aqueous layer was extracted
with ether and the combined organic layers were washed with
water and brine. The solution was dried with MgSO4 and
concentrated. The crude product was chromatographed (5:1
hexanes-ethyl acetate) to give 115 mg of 12 (83%) as a white
Com p ou n d 16.5 To a mixture of 15 (9.0 mg, 38.4 µmol) and
CH2Cl2 (0.5 mL) at -78 °C was added DIBALH (1.5 M in
toluene, 150 µL, 225 µmol) slowly dropwise. The mixture was
stirred for 30 min then quenched with methanol (0.1 mL).
Potassium sodium tartrate solution (5%) was then added and
the mixture extracted with ethyl acetate. The combined
organic layers were washed with water and brine then dried
with MgSO4. The crude product was chromatographed (5:1
solid: [R]25 +50.0 (c 12.9 mg/mL, CHCl3); mp 128 °C dec; 1H
D
NMR (CDCl3) δ 0.44-0.50 (m, 1H), 0.95-1.02 (m, 1H), 1.13-
1.20 (m, 4H), 1.22 (s, 3H), 1.29-1.36 (m, 4H), 1.59 (s, 3H), 2.06
(d, J ) 2.0 Hz, 3H), 2.39 (dd, J ) 7.6, 12.8 Hz, 1H), 2.52 (t, J
) 11.4 Hz, 1H), 2.71-2.79 (m, 1H), 4.20 (d, J ) 2.8 Hz, 1H);
13C NMR (CDCl3) δ 9.1, 13.9, 14.3, 23.5, 27.2, 27.4, 27.6, 32.6,
39.8, 71.5, 82.6, 83.3, 108.6, 126.3, 158.1, 198.8; IR (NaCl, thin
film) 2985, 2881, 1715, 1631, 1439 cm-1; MS (DCI/NH3) m/z
(% rel intensity) 313 (MH+ + 2, 4), 311 (MH+, 13), 277 (100);
hexanes-ethyl acetate) to give 4.1 mg of 16 (49%) as a yellow
1
gum: [R]25 -13.2 (c 1.7 mg/mL, CHCl3); H NMR (CDCl3) δ
D
0.80-1.05 (m, 3H), 1.15 (s, 3H), 1.20-1.28 (m, 1H), 1.61 (d, J
) 7.8 Hz, 1H), 1.84 (s, 3H), 2.06 (d, J ) 1.2 Hz, 3H), 2.85 (s,
1H), 4.32 (d, J ) 7.8 Hz, 1H), 6.07 (t, J ) 1.6 Hz, 1H), 6.33 (s,
1H); 13C NMR (CDCl3) δ 6.5, 13.1, 15.8, 16.3, 23.3, 29.8, 72.4,
73.0, 114.2, 130.8, 133.0, 138.2, 141.5, 150.7; IR (NaCl, thin
622 J . Org. Chem., Vol. 69, No. 3, 2004

Synthesis of Enantiomers of Antitumor Irofulven
film) 3407, 2973, 2926, 1629, 1445 cm-1; MS (20 eV) m/z (%
rel intensity) 234 (M+, 51), 216 (35), 201 (31), 173 (82), 159
(63), 145 (71), 43 (100); HRMS for C14H18O2 calcd 218.1307,
found 218.1310.
The enantiomer, (+)-acylfulvene, was prepared in the same
manner: [R]25 +476.0 (c 6.6 mg/mL, EtOH).
D
(-)-Acylfu lven e (3). To a solution of 16 (15.0 mg, 64.4
µmol) in DMSO (1.0 mL) was added IBX (29.6 mg, 0.105 mmol)
at room temperature. The mixture was stirred for 2 h then
diluted with water. The aqueous layer was extracted with ethyl
acetate and the combined organic layers were washed with
water and brine. The solution was dried with MgSO4 and the
crude product chromatographed (10:1 hexanes-ethyl acetate)
Ack n ow led gm en t. We are grateful to Dr. Peter
Gantzel for his X-ray crystallographic analysis. This
investigation was supported by funds provided by MGI
PHARMA, Inc., Minneapolis, MN, and by the Cigarette
and Tobacco Tax Fund of the State of California through
the Tobacco-Related Disease Research Program of the
University of California (award 12RT-0101).
to give 7.8 mg of 3 (53%) as an orange gum: [R]25 -493.4 (c
D
2.1 mg/mL, EtOH);11 1H NMR (CDCl3) δ 0.68-0.75 (m, 1H),
1.04-1.11 (m, 1H), 1.24-1.33 (m, 1H), 1.38 (s, 3H), 1.48-1.56
(m, 1H), 2.00 (s, 3H), 2.15 (s, 3H), 3.92 (br s, 1H), 6.43 (s, 1H),
7.17 (s, 1H); 13C NMR (CDCl3) δ 9.9, 14.6, 15.4, 17.1, 28.0, 37.4,
76.4, 120.7, 126.4, 136.1, 140.6, 142.6, 158.5, 197.9; IR (NaCl,
thin film) 3420, 1641 cm-1; MS (20 eV) m/z (% rel intensity)
216 (M+, 58), 201 (21), 188 (54), 173 (71), 159 (26), 145 (42),
43 (100); HRMS for C14H16O2 calcd 216.1150, found 216.1148.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
compounds 7-16, 3, and 4, and X-ray data for 7 and 12. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O035084J
J . Org. Chem, Vol. 69, No. 3, 2004 623