Total synthesis of (+)-ampullicin and (+)-isoampullicin: Two fungal metabolites with growth regulatory activity isolated from Ampulliferina sp. 27

Article abstract of DOI:10.1021/jo010527+

The total synthesis of the growth regulators (+)-ampullicin 1 and (+)-isoampullicin 2 from (R)-(-)-carvone 5 was accomplished by application of an 18-step sequence with 4.5% overall yield. The crucial step of the synthetic strategy lies on the internal displacement of tosylate 13 by means of the lactone enolate. In this way, access was opened to the tricyclic core present in these biologically active sesquiterpenic amides. A Horner-Emmons reaction between the carbaldehyde 16 and the phosphonate 22 led us to the stereoselective preparation of (+)-ampullicin 1. Standard transformation of 1 into the thermodynamically more stable geometric isomer (+)-isoampullicin 2 was trivial. The absolute configuration of both amides was established by X-ray analysis of a sample of synthetic (+)-isoampullicin 2.

Full text of DOI:10.1021/jo010527+

VOLUME 66, NUMBER 25
DECEMBER 14, 2001
© Copyright 2001 by the American Chemical Society
Articles
Tota l Syn th esis of (+)-Am p u llicin a n d (+)-Isoa m p u llicin : Tw o
F u n ga l Meta bolites w ith Gr ow th Regu la tor y Activity Isola ted
fr om Am pu llifer in a Sp . 27
Francisco A. Bermejo* and Rosario Rico-Ferreira
Departamento de Quı´mica Orga´nica, Facultad de Ciencias Qu´ımicas, Universidad de Salamanca,
Plaza de la Merced s.n., 37008 Salamanca, Spain
S. Bamidele-Sanni and Santiago Garc´ıa-Granda
Departamento de Quı´mica Fı´sica y Analı´tica, Facultad de Qu´ımica, Universidad de Oviedo,
J ulia´n Claverı´a 8, 3306 Oviedo, Spain
fcobmjo@gugu.usal.es
Received May 24, 2001
The total synthesis of the growth regulators (+)-ampullicin 1 and (+)-isoampullicin 2 from (R)-
(-)-carvone 5 was accomplished by application of an 18-step sequence with 4.5% overall yield. The
crucial step of the synthetic strategy lies on the internal displacement of tosylate 13 by means of
the lactone enolate. In this way, access was opened to the tricyclic core present in these biologically
active sesquiterpenic amides. A Horner-Emmons reaction between the carbaldehyde 16 and the
phosphonate 22 led us to the stereoselective preparation of (+)-ampullicin 1. Standard transforma-
tion of 1 into the thermodynamically more stable geometric isomer (+)-isoampullicin 2 was trivial.
The absolute configuration of both amides was established by X-ray analysis of a sample of synthetic
(+)-isoampullicin 2.
Sch em e 1
In tr od u ction
In the course of a screening program aimed at the
discovery of new plant growth regulators among fungal
metabolites, Kimura et al. reported the isolation of the
sesquiterpenic amides (-)-ampullicin 1, (+)-isoampullicin
2, and (+)-dihydroampullicin 3 (Scheme 1) from a culture
filtrate of an Ampulliferina-like fungus sp. No. 27 ob-
tained from a dead pine (Pinus thunbergii). These amides
were claimed to exhibit remarkable growth-regulating
properties.1,2
(1) Kimura, Y.; Nakajima, H.; Hamasaki, T.; Matsumoto, T.; Mat-
suda, Y.; Tsuneda, A. Agric. Biol. Chem. 1990, 54, 813-814.
(2) Kimura, Y.; Matsumoto, T.; Nakajima, H.; Hamasaki, T.; Mat-
suda, Y. Biosci. Biotech. Biochem. 1993, 57, 687-688.
Structural elucidation of 1-3 was made on the basis
of 1H NMR and 13C NMR data together with NOE
10.1021/jo010527+ CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/13/2001

8288 J . Org. Chem., Vol. 66, No. 25, 2001
Bermejo et al.
Sch em e 2. Retr osyn th etic An a lysis of
Sch em e 3a
(+)-Am p u llicin 1 a n d (+)-Isoa m p u llicin 2
difference experiments. However, to date the absolute
stereochemistry of these novel amides has not been
determined, although a biosynthetic pathway has been
envisioned that relates them to (+)-pinthunamide 4,
another fungal metabolite isolated from the same
Ampulliferina species whose absolute configuration was
determined by X-ray crystallographic analysis.3
In 1993 the total synthesis of (+)-pinthunamide 4 was
reported by Mori and Matsushima.4 The absolute con-
figuration of the synthetic product was determined by
comparison of its optical rotation value with that reported
for the natural product. However, to our knowledge there
is no reference in the literature about the synthesis of 1
a
Reaction and conditions: i: CH3C(OEt)3 (7 equiv), EtCOOH,
140 °C, 24 h, 85%; ii: NaOH, CH3OH, reflux, 2 h, 75%; iii:
N-hydroxysuccinimide, DCC, (S)-(-)-R-methylbenzylamine, CH2Cl2,
1 h, rt, 85%; iv: (from 8) NBS (1.1 equiv), acetone, 0 °C, 1 h, 85%;
v: nBu3SnH (1.1 equiv), AIBN, THF, 55 °C, 1 h, 95%; vi: O3,
CH2Cl2, -78 °C, S(Me)2, 15 h, rt, 85%; vii: m-CPBA (5 equiv),
NaHCO3, CH2Cl2, rt, 2 days, 85%; viii: NaOMe (1.1 equiv), MeOH,
0 °C, 45 min, 75%; ix: TBDMSCl (2.2 equiv), imidazole (2.5 equiv),
DMF, rt, 100%; x: LDA (1.1 equiv), HMPA, THF, -78 °C, allyl
bromide, 85%; xi: Bu4N+F-, THF, rt, 30 min, 85%; xii: TsCl, pyr,
DMAP, CH2Cl2, rt, 15 h, 90%; xiii: LDA (1.1 equiv), HMPA (1.2
equiv), -78 °C to room temperature, 90%.
and 2 except for previous communications about our own
5,6
synthetic work.
Here we report the full detailed total
synthesis of (+)-ampullicin 1 and (+)-isoampullicin 2
from (R)-(-)-carvone 5.
Our synthetic strategy is based on the internal dis-
placement of tosylate 13 and elongation of carbaldehyde
16 by a Horner-Emmons reaction with the heterocyclic
phosphonate 22. The absolute configuration of the target
molecules 1 and 2 was for the first time unequivocally
established by single-crystal X-ray diffraction of synthetic
(+)-isoampullicin, 2.
by DCC-promoted coupling reaction of 8 with enantio-
merically pure (S)-(-)-R-methylbenzylamine.6
The transformation of the acid 8 into the bicyclic
lactone 10 required the successful accomplishment of
three stereocontrolled transformations: (a) bromolacton-
ization, (b) tributyltin hydride reduction of the resulting
bromolactone, and (c) oxidative degradation of the iso-
propenyl moiety. The overall transformation of 8 into 10
was achieved by application of a six-step sequence with
37% overall yield.
Introduction of the allyl substituent was achieved by
addition of allyl bromide to a THF solution of the enolate
of 10 under kinetically controlled conditions. As expected,
the alkylation took place stereospecifically through the
exo face, leading to 11 as a single reaction product, which
has been isolated by flash chromatography on silica gel
with 85% yield. The transformation of 11 into the tosylate
13 was accomplished with excellent yield (80%) by O-silyl
deprotection, followed by treatment of the crude hydroxy
derivative 12 with tosyl chloride under standard condi-
tions.
The intramolecular displacement of tosylate 13 was
achieved by treatment of the bicyclic lactone with a THF
solution of LDA at -78 °C, followed by addition of HMPA,
leading to the tricyclic lactone 14 with 90% yield. The
spectroscopic properties obtained for 14 (Scheme 4) were
identical to those described for (1R,4S,6R,7S)-7-allyl-1-
methyl-9-oxatricyclo[4.3.0.04,7]nonan-8-one4 by Mori et
al.8
Oxidative degradation of the side chain in 14 was
accomplished very efficiently in two steps. Double-bond
isomerization of 14 led smoothly to the internal olefin
15 by treatment with rhodium(III) chloride hydrate with
quantitative yield. This was followed by ozonolysis of 15
to afford the rather stable carbaldehyde 16, also with
excellent yield. Assessment of the trans stereochemistry
Resu lts a n d Discu ssion
Our synthetic plan is based on the disconnection of the
exocyclic double-bond present in both target amides 1 and
2. We also made use of the “type a” disconnection to
access carbadehyde 16 from the bicyclic tosyloxy lactone
13, readily available from (R)-(-)-carvone 5 (Scheme 2).
The bicyclic lactone 10 was prepared from 5 by an
already reported procedure that has been successfully
developed by our group when we synthesized the tricyclic
lactone (1R,3R,6R,9S)-6,9-dimethyl-8-oxo-7-oxatricyclo-
[4.3.0.03,9]nonane. Enantiomerically pure (+)-trans-car-
veol 6 (Scheme 3) was obtained from its 3,5-dinitroben-
zoate following the J ohnston procedure.7 Following
standard protocols, the carboxylic acid 8 was obtained
from (+)-trans-carveol 6 by the ortho ester Claisen
rearrangement, followed by alkaline hydrolysis of the
resulting ethyl ester 7. The absolute stereochemistry of
8 has been previously confirmed beyond doubt by X-ray
analysis of the enantiomerically pure amide 9, obtained
(3) Kimura, Y.; Nakajima, H.; Hamassaki, T.; Sugawara, F.; Par-
kanyi, L.; Clardy, J . Tetrahedron Lett. 1989, 30, 1267-1270.
(4) Mori, K.; Matsushima, Y. Synthesis. 1993, 406-410.
(5) Rico. R.; Bermejo, F. Tetrahedron Lett. 1995, 36, 7889-7892.
(6) Rico, R.; Zapico, J .; Bermejo, F.; Sanni, S. B.; Garc´ıa-Granda, S.
Tetrahedron: Asymmetry. 1998, 9, 293-303.
(7) J ohnston, R. G.; Read, J . J . Chem. Soc. 1934, 233-237.
(8) Unfortunately, no optical rotation value for the tricyclic lactone
14 was available for comparison with that obtained by us, although
Mori and Matsushima had reported [R]D values of their more advanced
intermediates. Prof. K. Mori, Science University of Tokyo, personal
communication.
1
on the exocyclic double bond in 15 was confirmed by H
NMR irradiation experiments. The preparation of 16 by
(9) Martin, M. J .; Bermejo, F. Tetrahedron Lett. 1995, 36, 7705-
7708.

Total Synthesis of (+)-Ampullicin
J . Org. Chem., Vol. 66, No. 25, 2001 8289
Sch em e 4a
a
Reaction conditions: i: RhCl3xH2O, EtOH, reflux, 1.5 h, 100%;
ii: O3, CH2Cl2, -78 °C, SMe2, rt, 3 h, 100%; iii: 22, NaH, THF,
rt, 2 h, 80%; iv: TFA, CH2Cl2, 0 °C, 30 min, 95%; v: I2, CHCl3,
reflux, 5 h, 100%.
F igu r e 1. ORTEP diagram for (+)-isoampullicin 2. An
arbitrary numbering system is given.
Sch em e 5a
Sch em e 6. Ster eoselectivity of th e
Hor n er -Em m on s Rea ction : Develop in g
In ter a ction s on th e Tr a n sition Sta tes TS-1 a n d
TS-2 Lea d in g to 23 a n d 24
a
Reaction conditions: i: (tBuOCO)2O, THF, reflux, 95%; ii:
LDA, THF, -78 °C, PhSeCl, 85%; iii: AcOH, H2O2, 90%; iv: NBS
(1 equiv), AIBN, CCl4, 80 °C, 3 h, 100%; v: P(OEt)3 (2 equiv), 140
°C, 1 h, 100%.
this procedure represents a remarkable improvement
with respect to other previously reported alternatives.5
Transformation of carbaldehyde 16 into N-Boc ampul-
licin 23, was successfully achieved by a Horner-Emmons
reaction with phosphonate 22 (Scheme 5). This reagent
was readily obtained from commercially available 3-meth-
yl-2-pyrrolidinone 17. Nitrogen protection was followed
by reaction of 18 with a THF solution of LDA at -78 °C
and further addition of phenylselenyl chloride. Flash
chromatography of the crude product afforded the pure
R-selenoderivative 19 with 86% yield. Oxidation of 19
with hydrogen peroxide in acetic acid at 0 °C led to
spontaneous elimination of PhSeOH and allowed us to
isolate the N-Boc-3-methyl-3-pyrrolin-2-one 209 with 90%
yield. Appropriate functionalization at the C-5 site of
pyrrolinone 20 was successfully achieved in two steps.
The allylic bromination of 20 was achieved by treatment
with NBS and AIBN in carbon tetrachloride at 85 °C.
Isolation of the pure bromide 21 was achieved by flash
chromatography on silica gel with 75% yield. Finally,
reaction of 21 with triethyl phosphite at 140 °C led to
the crude phosphonate 22, which was used without
further purificaton.10
Treatment of phosphonate 22 with sodium hydride in
THF followed by addition of carbaldehyde 16 at room
temperature led to the exclusive formation of N-Boc
ampullicin 23. No trace of the geometrical isomer 24 was
detected by 1H NMR analysis of the crude reaction
mixture. Flash chromatography of the crude product led
to the isolation of pure 23 with 75% yield.
The stereoselectivity of the olefination process may be
explained in terms of steric hindrance, which influences
the diastereomeric transition states of the Horner-
Emmons reaction; the strong steric interactions devel-
oped in TS-2 between the side chain and the N-Boc
protecting group will lead to the exclusive formation of
23 via the TS-1 transition state (Scheme 6).
Deprotection of 23 by treatment with trifluoroacetic
acid in dichloromethane at 0 °C led exclusively to
ampullicin 1 with excellent yield (95%). The thermody-
namically more stable geometrical isomer isoampullicin
2, was prepared quantitatively by isomerizing the E
isomer 1 by treatment with iodine in refluxing chloroform
for 5 h.
The spectroscopic properties recorded for both synthetic
geometrical isomers completely matched those described
in the literature for ampullicin 1 and isoampullicin 2.1
Unexpectedly, however, synthetic ampullicin 1 displayed
a positive specific rotation, whereas for the compound
isolated from natural sources a negative rotation was
reported.11 Therefore, a single-crystal of synthetic 2
suitable for X-ray crystallography was grown from a
hexane-acetone mixture, and the correct stereochemistry
12
of 2 was established (Figure 1).
Since synthetic (+)-isoampullicin 2 was obtained from
1 through unequivocal chemical transformations, the
stereochemistry corresponding to both synthetic products
is established beyond doubt.13
Con clu sion
The convergent total synthesis of the growth regulators
(+)-ampullicin 1 and (+)-isoampullicin 2 is described,
using commercially available (R)-(-)-carvone, by applica-
tion of a stereoselective 18-step synthetic sequence with
(10) Reaction of 21 with triphenylphosphine led mainly to the
formation of the alkoxyphosphonium bromide. See House, H. O.
Modern Synthetic Methods; 2nd ed.; Benjamin-Cummings Publishing
Company; Menlo Park CA, 1972; p 698.

8290 J . Org. Chem., Vol. 66, No. 25, 2001
Bermejo et al.
later, 15 mL of a saturated aqueous solution of NH4Cl was
added, and the mixture was left to reach room temperature.
After extraction with AcOEt, the combined organic phases
were washed with brine, dried (Na2SO4), and evaporated at
reduced pressure. The residue (558 mg) was purified by flash
chromatography (hexane/AcOEt 9:1) to yield 389.2 mg (85%)
of 11 [R]D25 ) +12.3 (c ) 0.79, CHCl3). IR (CHCl3) ν 2932, 2859,
4.5% overall yield. This synthetic route should give access
to the fungal metabolites (+)-dihydroampullicin 3 and
(+)-pinthunamide 4, sesquiterpenic amides isolated from
Ampulliferina Sp. 27.
Exp er im en ta l Section
1
1767, 1643, 1464, 1096, 866 cm-1. H NMR (CDCl3) δ 0.05 (s,
Gen er a l P r oced u r es. NMR spectra were recorded at 250,
300, or 400 MHz for 1H (δ, Me4Si, CDCl3 except where
otherwise indicated) and 62.83, 75.73, or 100.63 MHz for 13C
(δ, CDCl3, carbon multiplicities assigned by DEPT techniques)
except where otherwise indicated. Low-resolution electron
impact mass spectrum data (MS-EI) were obtained at 70 eV
unless otherwise stated. Optical rotations were measured with
Na 589 nm irradiation. Melting points are uncorrected. Kugel-
rohr distillation oven temperatures (ot) refer to the external
air bath temperature. All reactions were carried out under
argon. Silica gel flash chromatography purifications were
performed on silica gel (230-400 mesh) as described by Still.14
Ozone was generated in a Fischer 502 ozone generator. TLC
was performed on plates of silica gel (2 × 5 cm, 0.2 mm
thickness). Components were located by observation of the
plates under UV light and/or by treating the plates with
phosphomolybdic reagent, followed by heating. All glassware
was dried at 150 °C overnight, assembled hot, and allowed to
cool in a stream of dry argon. All transfers of solutions and
solvents were performed by syringe techniques or via cannula.
All solvents were freshly distilled from the appropriate drying
agent before use. Diethyl ether, tetrahydrofuran, toluene, and
benzene were freshly distilled from sodium benzophenone ketyl
under an argon atmosphere. Carbon tetrachloride and dichlo-
romethane were distilled from P2O5 under argon. Pyridine was
distilled first from KOH and later from CaH2 under argon.
Dimethylformamide was distilled from P2O5 under reduced
pressure and stored over 4A MS. Ethyl acetate, hexanes, and
dimethyl sulfide were distilled fron CaH2 under nitrogen.
Diisopropylamine was distilled twice from CaH2 under nitro-
gen and stored over 4 Å MS. Methanol was distilled from Mg
under argon. m-CPBA was crystallized from dichloromethane.15
Concentrations were carried out in a rotatory evaporator.
Solutions were dried with Na2SO4. All the new compounds
exhibited satisfactory low resolution MS data and afforded
combustion analyses or appropriate exact mass data of the
molecular ions. 3-Methyl-2-pyrrolidinone was commercially
available from Lancaster Synthesis Ltd, Strasbourg, France.
(3R,3aR,5R,7aR)-5-ter t-Bu tyldim eth ylsilyloxy-7a-m eth -
yl-3-(2-p r op en yl)-3a ,4, 5,6,7,7a -h exa h yd r o-2(3H)-ben zo-
fu r a n on e (11). To a solution of diisopropylamine (0.3 mL, 1.97
mmol) in 5 mL of anhydrous THF a solution of 1.1 M BuLi in
hexane (1.7 mL) was added at -78 °C. After stirring under
Ar for 45 min, HMPA (0.32 mL, 1.83 mmol) and 400 mg (1.41
mmol) of 106 in 2 mL of anhydrous THF were added. The
mixture was stirred at this temperature for 1 h, after which
allyl bromide (0.30 mL, 3.52 mmol) was added. Thirty minutes
6H), 0.88 (s, 9H), 1.49 (s, 3H), 1.2-2.2 (m, 6H), 2.3-2.7 (m,
4H), 3.78 (m, 1H), 5.12 (m, 2H), 5.81 (m, 1H) ppm. 13C NMR
(CDCl3) δ -4.78, 17.99, 24.46, 25.72, 31.98, 33.14, 33.43, 33.67,
43.38, 46.82, 66.52, 82.16, 117.71, 134.59, 176.47 ppm. FAB-
MS m/z (relative intensity) 325.1 (23), 193.1 (33), 147.1 (70).
Anal. Calcd for C18H32O3Si: C, 66.61; H, 9.94. Found: C, 66.56;
H, 9.87.
(3R,3a R,5R,7a R)-5-Hyd r oxy-7a -m eth yl-3-(2-p r op en yl)-
3a ,4,5,6,7,7a -h exa h yd r o-2(3H)-ben zofu r a n on e (12). To a
solution of 11 (389.2 mg, 1.20 mmol) in 25 mL of THF was
added a solution of Bu4NF‚H2O (757 mg, 2.4 mmol) in 5 mL of
THF. The mixture was stirred under Ar at room temperature
for half an hour and then evaporated at reduced pressure. Ten
milliliters of a saturated aqueous solution of NH4Cl was added,
and the aqueous phase was extracted with Cl2CH2. The
combined organic phases were washed with brine, dried (Na2-
SO4), and evaporated at reduced pressure. The crude was
purified by flash chromatography (hexane/AcOEt 3:7) to yield
215 mg (85%) of 12 [R]25D ) -7.8 (c ) 1.09, CHCl3). IR (CHCl3)
1
ν 3430, 2938, 1759, 1642, 1092, 934 cm-1. H NMR (CDCl3) δ
1.48 (s, 3H), 1.20-1.75 (m, 6H),1.8-2.8 (m, 4H), 3.82 (m, 1H),
5.15 (m, 2H), 5.80 (m, 1H) ppm. 13C NMR (CDCl3) δ 24.36,
31.59, 32.31, 32.94, 33.54, 43.13, 46.34, 65.55, 82.35, 117.92,
134.10, 176.75 ppm. FAB-MS m/z (relative intensity) 211.1
(37), 193.1 (22), 149.0 (100), 113.0 (23), 80.8 (23). Anal. Calcd
for C12H18O3: C, 68.54; H, 8.63. Found: C, 68.47; H, 8.54.
(3R,3a R,5R,7a R)-5-(p-Tolu en esu lfon yloxy)-7a -m eth yl-
3-(2-p r op en yl)-3a ,4,5,6,7,7a -h exa h yd r o-3(2H)-ben zofu r a -
n on e (13). To a solution of 12 (235.1 mg, 1.12 mmol) in 3 mL
of anhydrous CH2Cl2 were added pyridine (0.18 mL, 2.24
mmol), a catalytic amount of 4-(dimethylamino)pyridine, and
TsCl (320 mg, 1.7 mmol). The mixture was stirred under Ar
at room temperature for 35 h and then poured into an aqueous
solution of NaHCO3 and extracted with CH2Cl2. The combined
organic phases were washed with 1 N HCl, 10% NaHCO3, and
brine, dried (Na2SO4), and evaporated under reduced pressure.
The crude was purified by flash chromatography (hexane/
AcOEt 8:2) to yield 16.5 mg (7%) of starting material and 367
mg (90%) of 13 mp 141-143 °C (hexane/AcOEt); [R]25D ) +15.1
(c ) 1.02, CHCl3). IR (CHCl3) ν 3055, 2953, 1765, 1643, 1599,
1
1265, 739 cm-1. H NMR (CDCl3) δ 1.46 (s, 3H), 1.4-2.5 (m,
10H), 2.46 (s, 3H), 4.51 (m, 1H), 5.05 (m, 2H), 5.65 (m, 1H),
7.35 (d, 2H, J ) 8.34 Hz), 7. 78 (d, 2H, J ) 8.34 Hz) ppm. 13C
NMR (CDCl3) δ 21.46, 24.35, 28.88, 29.79, 33.10, 33.24, 42.95,
46.04, 76.46, 81.12, 118.12, 127.60, 129.85, 133.92, 134.01,
144.81, 175.78 ppm. FAB-MS m/z (relative intensity) 365.0.-
(58), 262.5 (20), 193.1 (100), 153.5 (85), 108.5 (71), 78.4 (52),
52 (68). Anal. Calcd for C19H24O5S: C, 62.61; H, 6.64. Found:
C, 62.56; H, 6.58.
(11) In
a
previous communication on our synthetic work5 we
(1R,4S,6R,7S)-7-Allyl-1-m eth yl-9-oxa tr icyclo[4.3.0.04,7]-
n on a n -8-on e (14). To a solution of diisopropylamine (0.5 mL,
3.1 mmol) in 5 mL of anhydrous THF a solution of 1.1 M BuLi
in hexane (2.8 mL, 3.12 mmol) was added at -78 °C. The
mixture was stirred under Ar for an hour at this temperature,
after which HMPA (0.54 mL, 3.1 mmol) and a solution of 13
(948 mg, 2.6 mmol) in 10 mL of anhydrous THF were dropwise
added. After stirring for 2 h (from -78 °C to room tempera-
ture), 25 mL of a saturated aqueous solution of NH4Cl was
added, and the aqueous phase was extracted with AcOEt. The
combined organic phases were washed with brine, dried (Na2-
SO4), and evaporated under reduced pressure. The residue was
purified by flash chromatography (hexane/AcOEt 7:3) to yield
456 mg (90%) of 14 [R]25D ) -2.2 (c ) 1.10, CHCl3). IR (CHCl3)
mistakenly reported a complete agreement of the physical properties
of natural ampullicin with those obtained for the synthetic product.
Obviously, this is true except for the specific rotation value as is clearly
explained in the text. However, our synthetic (+)-isoampullicin 2
resulted to be insoluble in methanol and was found to be dextrorotatory
in chloroform. Thanks are given to Prof. Y. Kimura (Tottori University,
J apan) for providing us with the 1H NMR spectra of natural 1, 2, 3,
and 4. Unfortunately, no sample of natural 1 was available.
(12) Correspondence regarding the X-ray crystallographic determi-
nation of the absolute configuration of 2 should be addressed to Prof.
Santiago Garcia-Granda (University of Oviedo, Spain).
(13) Since the absolute stereochemistry of 8 has been previously
demostrated by our group and the overall transformation of carboxylic
acid 8 into (+)-ampullicin 1 has been achieved through stepwise
stereocontrolled transformations, we claim that the absolute stereo-
chemistry of synthetic (+)-isoampullicin 2 is identical to that depicted
in Scheme 1. Additionally, X-ray analysis of
a pure sample of
1
ν 3077, 2934, 1761, 1642, 1200, 912 cm-1. H NMR(CDCl3) δ
(+)-isoampullicin 2 (Figure 1) supports our proposal.
(14) Still, W. C.; Kahn, M.; Mitra, A. J . Org. Chem. 1978, 43, 2923.
(15) Traylor, T. G.; Miksztal, A. R., J . Am. Chem. Soc. 1987, 109,
1.45 (s, 3H), 1.68 (d, 1H, J ) 10.5 Hz), 1.90 (s, 4H), 2.21 (dt,
1H, J ) 5.1 Hz, 10.2 Hz), 2.33 (dd, 1H, J ) 8.2 Hz, 15.0 Hz),
2.41 (m, 1H), 2.48 (t, 1H, J ) 5.1 Hz), 2.65 (dd, 1H, J ) 8.2
2770.

Total Synthesis of (+)-Ampullicin
J . Org. Chem., Vol. 66, No. 25, 2001 8291
1776, 1720, 1475, 1440, 1368, 1300, 1155 cm-1 1H NMR
(CDCl3) δ 1.52 (s, 9Η); 1.59 (s, 3Η); 2.15 (m, 2H); 3.50 (m, 2H);
7.50 (m, 5H) ppm. 13C NMR (CDCl3) δ 23.60; 27.67; 33.22;
42.63; 49.39; 82.19; 125.92; 128.60; 129.17; 137.39; 149.77;
173.50 ppm. EI-MS m/z (relative intensity): 355 (22); 254 (9);
Hz, 15.0 Hz), 5.07-5.16 (m, 2H), 5.65-5.86 (m, 1H) ppm. 13C
NMR (CDCl3) δ 22.56, 22.91, 24.50, 29.75, 33.82, 40.86, 46.45,
55.27, 87.59, 117.61, 133.13, 177.33 ppm. FAB-MS m/z (rela-
tive intensity) 193.1 (30), 184.1 (100), 149.0 (34), 90.9 (20), 83.8
(32). Anal. Calcd for C12H16O2: C, 74.97; H, 8.39. Found: C,
74.89; H, 8.28.
.
157 (60); 124 (31); 98 (100); 57 (100). Anal. Calcd for C16H21
-
(1R ,4S ,6R ,7R )-1-Me t h y l-9-o x a -7-[-(E )-1-p r o p e n y l]-
tr icyclo[4.3.0.04,7]n on a n -8-on e (15). To a solution of 14 (409
mg, 2.1 mmol) in 12 mL of degassed EtOH under Ar was added
rhodium(III) chloride hydrate (16 mg, 0.063 mmol). The
mixture was heated under reflux and stirred for 1.5 h. After
evaporation, the crude product was purified by flash chroma-
tography (hexane/ether 7:3) to yield 408 mg (100%) of 15:
NO3Se: C, 54.24; H, 5.97; N, 3.95. Found: C, 54.16; H, 5.82;
N, 3.82.
1-ter t-Bu toxyca r bon yl-3-m eth yl-3-p yr r olin -2-on e (20).
To a solution of 1-tert-butoxycarbonyl-3-methyl-3-phenylsele-
nyl-2-pyrrolidinone (19) (5 g, 14 mmol) in 100 mL of freshly
distilled THF were successively added glacial acetic acid (3
mL) and 30% hydrogen peroxide (27 mL). The reaction was
stirred for 30 min, 1 M NaHCO3 (5 mL) was added, and the
reaction was extracted with AcOEt, washed with brine and
dried over Na2SO4 to afford 20 (2.5 g, 90%), mp 72-74 °C
(hexane). IR (CHCl3) ν 2936, 1770, 1722, 1657, 1475, 1453,
[R]25 ) +38.0 (c ) 0.93, CHCl3). IR (CHCl3) ν 2936, 1765,
D
1454, 1200, 1017, 756 cm-1. 1H NMR (CDCl3, 400 MHz) δ 1.47
(s, 3H), 1.62 (d, 1H, J ) 10.22 Hz), 1.75 (d, 3H, J ) 4.96 Hz),
1.87-1.95 (m, 4H), 2.23 (ddd, 1H, J ) 10.2 Hz, 5.1 Hz, 5.1
Hz), 2.58-2.62 (m, 2H), 5.60-5.80 (m, 2H, J trans ) 15.6 Hz)
ppm. 13C NMR (CDCl3,400 MHz) δ 18.15, 23.00, 23.11, 24.90,
29.84, 41.68, 48.84, 57.42, 87.93, 126.23, 127.42, 177.42 ppm.
EI-MS m/z (relative intensity) 192.20 (15), 177.15 (15), 151.10
(50), 137.15 (48), 105.10 (48), 91.15 (62), 79.20 (57), 55.15 (39),
43.10, (100). Anal. Calcd for C12H16O2: C, 74.97; H, 8.39.
Found: C, 74.85; H, 8.31.
1
1160 cm-1. H NMR (CDCl3) δ 1.52 (s, 9Η); 1.85 (q, 3Η, J )
2.5 Hz); 4.16 (quint, 2H, J ) 2.5 Hz); 6.76 (sext, 1H, J ) 2.5
Hz) ppm. 13C NMR (CDCl3) δ 10.70, 27.86, 49.22; 82.47; 135.23;
137.73; 149.60; 169.64 ppm. EI-MS m/z (relative intensity):
182 (M+ - CH3, 5); 142 (57); 124 (71); 110 (8); 98 (50); 81 (6);
69 (21); 57 (100). Anal. Calcd for C10H15NO3: C, 60.90; H, 7.67;
N, 7.10. Found: C, 60.81; H, 7.72, N, 7.22.
(1R,4S,6R,7S)-1-Meth yl-9-oxa -8-oxotr icyclo[4.3.0.04,7]-
n on a n -7-ca r ba ld eh yd e (16). Ozone was bubbled through a
solution of alkene 15 (370.5 mg, 1.9 mmol) in 25 mL of CH2-
Cl2 at -78 °C until a blue-grey coloration developed. Then,
excess ozone was eliminated with argon, and SMe2 (0.9 mL,
12.3 mmol) was added. After stirring for 3 h (from -78 °C to
room temperature) the solvent was evaporated under reduced
pressure. The residue was purified by flash chromatography
(hexane/AcOEt 6:4) to yield 345 mg (100%) of 16 [R]25D ) +15.2
(c ) 1.02, CHCl3). IR (CHCl3) ν 2976, 1761, 1721, 1267, 737
5-Br om o-1-ter t-bu toxyca r bon yl-3-m eth yl-3-p yr r olin -2-
on e (21). To a solution of 1-tert-butoxycarbonyl-3-methyl-2-
pyrrolin-2-one (20) (1 g, 5.5 mmol) in 50 mL of CCl4 were added
NBS (983 mg, 5.5 mmol) and a catalytic amount of AIBN. The
mixture was stirred for 3 h at 80 °C under an argon atmo-
sphere. After cooling, the solution was filtered and the solvent
evaporated under reduced pressure. The residue was dissolved
in CH2Cl2 (10 mL), and the organic phase was washed with
water and brine and then dried (Na2SO4) and evaporated
under reduced pressure to give a crude product (1.2 g, 100%),
which was purified by flash chromatography on silica gel.
Elution with (hexane/AcOEt 8:2) led to 21 (0.9 g, 75%), IR
(film) ν 3057, 1786, 1751, 1655, 1371, 1346, 1265, 1151, 1040,
cm-1 1H NMR (CDCl3) δ 1.50 (s, 3H), 1.63 (d, 1H, J ) 11.0
.
Hz), 1.66-1.97 (m, 4H), 2.34 (ddd, 1H, J )11.0 Hz, 5.5 Hz,
5.5 Hz), 2.99 (t, 1H, J ) 5.5 Hz), 3.08 (m, 1H), 9.84 (s, 1H)
ppm. 13C NMR (CDCl3) δ 22.93, 23.22, 24.37, 29.63, 40.43,
47.65, 64.28, 88.89, 173.32, 196.02 ppm. Anal. Calcd for
1
953, 851, 772, 739, 704 cm-1. H NMR (CDCl3) δ 1.52 (s, 9H),
1.88 (s, 3H), 6.39 (d, 1H, J ) 1.5 Hz), 6.86 (quint, 1H, J ) 1.7
Hz) ppm. 13C NMR (CDCl3) δ 10.41, 27.64, 57.73, 84.05, 134.40,
140.53, 147.40, 166.69 ppm. EI-MS m/z (relative intensity):
260 (M+ - CH3, 5); 196 (M+ - Br, 10); 176 (8); 96 (90); 57
(100). Anal. Calcd for C10H14O3BrN: C, 43.50; H, 5.11; N, 5.07.
Found: C, 43.47; H, 5.06; N, 5.16.
C
10H12O3: C, 66.65; H, 6.71. Found: C, 66.58; H, 6.65.
1-ter t-Bu toxyca r bon yl-3-m eth yl-2-p yr r olid in on e (18).
To a solution of 3-methyl-2-pyrrolidinone 17 (5.90 g, 53.5
mmol) in 100 mL of freshly distilled THF, triethylamine (8.9
mL, 64.2 mmol), 4-(dimethylamino)pyridine (60 mg, 0.5 mmol),
and di-tert-butyl dicarbonate (14 g, 64.2 mmol) were succes-
sively added. The reaction mixture was stirred for 4 h at room
temperature and then diluted with ethyl acetate. The organic
layer was washed with citric acid (5%) and brine. The organic
layer was dried with Na2SO4, and the solvent was evaporated
off under reduced pressure to yield 18 (10 g, 95%). IR(film) ν
(1-ter t-Bu toxyca r bon yl-3-m eth yl-3-p yr r olin )-5-yl-p h os-
p h on ic Acid Dieth yl Ester (22). A solution of 21 (1 g, 3.6
mmol) and triethyl phosphite (1.15 mL, 7.2 mmol) was stirred
at 140 °C for 1 h under an argon atmosphere. After cooling,
the excess of reagent was eliminated by evaporation under
reduced pressure to yield phosphonate 22 (1.2 g, 100%), which
was used without further purification: IR (film) ν 2982, 1778,
3000, 1768, 1724, 1460, 1365, 1312, 1152 cm-1 1H NMR
.
(CDCl3) δ 1.15 (d, 3H, J ) 7 Hz); 1.46 (s, 9H); 2.14 (m, 2H);
2.47 (m, 1H); 3.57(m, 2H) ppm. 13C NMR (CDCl3) δ 14.74;
25.83; 27.45; 37.94; 43.73; 81.79; 149.76; 175.77ppm. EI-MS
m/z (relative intensity): 199 (M+,4); 184 (17); 144 (51); 126
(49); 114 (13); 100 (73); 85 (9); 70 (44); 57 (100). Anal. Calcd
for C10H17NO3: C, 60.28; H, 8.60; N, 7.03. Found: C, 60.33;
H, 8.72, N, 7.10.
1736, 1316, 1258, 1159, 1026, 959 cm-1 1H NMR (CDCl3) δ
.
1.30 (m, 6H), 1.55 (s, 9H), 1.89 (m, 3H), 4.12 (m, 4H), 4.93
(dquint, 1H, J ) 17.1 Hz, 2.2 Hz), 6.87 (m, 1H) ppm. 13C NMR
(CDCl3) δ 11.23, 16.40, 16.43, 28.15, 57.94, 63.52, 63.66, 83.64,
135.99, 137.39, 149.33, 169.28 ppm. EI-MS m/z (relative
intensity): 333 (5), 289 (5), 260 (10), 233 (60), 205 (12), 177
(25), 123 (20), 96 (40), 81 (20), 57 (100). Anal. Calcd for C14H24
-
1-ter t-Bu toxycar bon yl-3-m eth yl-3-ph en ylselen yl-2-pyr -
r olid in on e (19). To a solution of diisopropylamine (1.8 mL,
13 mmol) in 15 mL of THF was dropwise added 7.5 mL solution
of BuLi (1.6 M in hexane) at 0 °C. The reaction was stirred
for 1 h at this temperature; then, a solution of 1-tert-
butoxycarbonyl-3-methyl-2-pyrrolidinone (18) (2 g, 10 mmol)
in 15 mL of THF was added at -78 °C, and the reaction
mixture was stirred for 1 h. This was followed by the addition
of a solution of PhSeCl (1.8 g, 10 mmol) in 2 mL of THF, and
stirring at this temperature was continued for 1 h. The
reaction was then allowed to warm to room temperature and
was then quenched by the addition of a sat. aqueous NH4Cl
solution. The reaction product was extracted with AcOEt, and
the organic layer was washed with brine and dried with Na2-
SO4 to afford a crude product which was fractionated by flash
chromatography on silica gel. Elution with (hexane/AcOEt 8:2)
led to 19 (3 g, 85%), mp 86-88 °C (hexane). IR (CHCl3) ν 3010,
NPO6: C, 50.45; H, 7.26; N, 4.20. Found: C, 50.56; H, 7.37;
N, 4.12.
(1′R,4′S,6′R,7′R,E)-1-ter t-Bu t oxyca r b on yl-3-m et h yl-5-
(1′-m et h yl-8′oxo-9′-oxa t r icyclo[4.3.0.04,7]n on -7′-yl)m et h -
ylen e-3-p yr r olin -2-on e, N-Boc-Am p u llicin (23). To a sus-
pension of 60% NaH dispersion in mineral oil (200 mg, 5 mmol)
in 25 mL of anhydrous THF was added dropwise a solution of
phosphonate 22 (1.6 g, 5 mmol) in 5 mL of freshly distilled
THF. The mixture was stirred under Ar at room temperature
for 1 h, and then a solution of carbaldehyde 16 (449 mg, 2.5
mmol) in 15 mL of anhydrous THF was added. After stirring
for 2 h at the same temperature, 5 mL of a saturated aqueous
solution of NH4Cl was added, and the aqueous phase was
extracted with AcOEt. The combined organic phases were
washed with brine, dried (Na2SO4), and evaporated under
reduced pressure. The residue was purified by flash chroma-
tography (hexane/AcOEt 7:3) to yield 23 (632 mg, 80%), mp

8292 J . Org. Chem., Vol. 66, No. 25, 2001
Bermejo et al.
127-129 °C (hexane) [R]25 ) +83.8 (c ) 0.95, CHCl3). IR
a m p u llicin (2). To a solution of 1 (175 mg, 067 mmol) in 1
mL of CHCl3 was added a catalytic amount of iodine (25 mg),
and the mixture was stirred under argon, under reflux for 5
h, and then at room-temperature overnight. The residue
obtained by evaporation of the solvent was purified by flash
chromatography (hexane/AcOEt 1:1) to yield 2 (174 mg, 100%),
D
(CHCl3) ν 2932, 1771, 1738, 1456, 1300, 1157, 1084 cm-1. H
1
NMR (CDCl3) δ 1.50 (s, 3H), 1.56 (s, 9H), 1.72 (d, 1H, J ) 11.2
Hz), 1.92 (s, 3H), 1.96-2.01 (m, 4H), 2.41 (ddd, 1H, J )11.2
Hz, 5.6 Hz, 5.6 Hz), 2.7 (d, 2H, J ) 5.6 Hz), 6.71 (s, 1H), 6.79
(s, 1H) ppm. 13C NMR (CDCl3) δ 10.71, 23.17, 23.90, 24.80,
28.06, 29.75, 47.51, 52.88, 56.16, 83.55, 87.81, 114.87, 132.02,
132.66, 139.87, 149.59, 167.64, 175.57 ppm. Anal. Calcd for
C20H25NO5: C, 66.83; H, 7.01; N, 3.90. Found: C, 66.78; H,
6.95; N, 3.82.
mp 205-208 °C (hexane); [R]25 ) +108 (c ) 0.50, CHCl3). IR
D
(CHCl3) ν 3182, 1752, 1694, 1658 cm-1 1H NMR (CDCl3) δ
.
1.52 (s, 3H), 1.75 (d, 1H, J ) 10.6 Hz), 1.95 (d, 3H, J ) 1.5
Hz), 1.91-2.10 (m, 4H), 2.39 (ddd, 1H, J )10.6 Hz, 5.4 Hz,
5.4 Hz), 2.77 (d, 2H, J ) 5.4 Hz), 5.15 (s, 1H), 6.61(t, 1H, J )
1.6 Hz), 8.35 (s, 1H) ppm. 13C NMR (CDCl3) δ 10.38, 23.30,
23.78, 24.71, 29.75, 49.95, 51.24, 56.28, 88.50, 106.87, 133.37,
134.15, 140.08, 172.82, 176.27 ppm. EI-MS m/z (relative
intensity): 259.10 (68), 218.05 (48), 204.00 (75), 187.05 (28),
174.05 (22), 147.95 (31), 133.95 (100), 104.00 (12), 77.00 (18).
Anal. Calcd for C15H17NO3: C, 69.48; H, 6.61; N, 5.40. Found:
C, 69.47; H, 6.60; N, 5.38.
(1′R,4′S,6′R,7′R,E)-3-Met h yl-5-(1′-m et h yl-8′oxo-9′-oxa -
tr icyclo [4.3.0.04,7]n on -7′-yl)m eth ylen e-3-p yr r olin -2-on e,
Am p u llicin (1). To a solution of 23 (236.8 mg, 0.64 mmol) in
1 mL of CH2Cl2 was added trifluoroacetic acid (0.12 mL, 1.6
mmol) at 0 °C, and the mixture was stirred under argon for
half an hour. After evaporation under reduced pressure, 1 N
NaHCO3 (2 mL) was added, and the reaction mixture was
extracted with AcOEt. The organic layers were washed with
brine and dried with Na2SO4. Evaporation of the solvent
afforded a crude product which was fractionated by flash
chromatography (hexane/AcOEt 1:1) to yield 1 (153.6 mg, 95%),
Ack n ow led gm en t. Financial support of this work
by the Direccion General de Investigacio´n Cient´ıfica y
Te´cnica, Spain (DGICYT PB98-0251) and the J unta de
Castilla y Leo´n (SA 24/00B) is gratefully acknowledged.
mp 195-198 °C (hexane); [R]25 ) +109.7 (c ) 0.75, CHCl3).
D
IR (CHCl3) ν) 3105, 1767, 1733, 1708 cm-1. H NMR (CDCl3)
1
δ 1.53 (s, 3H), 1.76 (d, 1H, J ) 10.7 Hz), 1.98 (s, 3H), 1.95-
2.16 (m, 4H), 2.39 (ddd, 1H, J )10.7 Hz, 5.3 Hz, 5.3 Hz), 2.77
(d, 2H, J ) 5.3 Hz), 5.49 (s, 1H), 6.73 (s, 1H), 7.88 (s, 1H) ppm.
13C NMR (CDCl3): δ) 10.97, 23.05, 23.81, 24.91, 29.66, 46.72,
52.66, 55.96, 87.98, 109.21, 128.56, 136.37, 141.02, 171.72,
176.09 ppm. EI-MS m/z (relative intensity): 259.10 (60), 218.05
(50), 204.05 (80), 187.05 (30), 133.95 (100), 110.00 (10), 91.00
(20). Anal. Calcd for C15H17NO3: C, 69.48; H, 6.61; N, 5.40.
Found: C, 69.56; H, 6.71; N, 5.36.
Su p p or tin g In for m a tion Ava ila ble: Spectroscopic data
for compounds 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 23, 1,
and 2 (14 compounds). Tables of the crystal data, bond lengths
and angles, atomic coordinates, and anisotropic thermal
parameters obtained for (+)-isoampullicin, 2. This material is
available free of charge via the Internet at http://pubs.acs.org.
(1′R,4′S,6′R,7′R,Z)-3-Meth yl-5-(1′-m eth yl-8′-oxo-9′oxatr i-
cyclo [4.3.0.04,7]n on -7′-yl)m eth ylen e-3-p yr r olin -2-on e; Iso-
J O010527+