Total synthesis of isoroquefortine C

Article abstract of DOI:10.1021/jo0106593

A short and efficient total synthesis of isoroquefortine C, the 3,12-(Z)-isomer of roquefortine C, from L-tryptophan methyl ester hydrochloride and 4(5)-(hydroxy)methylimidazole hydrochloride is described.

Full text of DOI:10.1021/jo0106593

620
J . Org. Chem. 2002, 67, 620-624
Tota l Syn th esis of Isor oqu efor tin e C
Bruno M. Schiavi, David J . Richard, and Madeleine M. J oullie´*
Department of Chemistry, University of Pennsylvania, 231 South 34th Street,
Philadelphia, Pennsylvania 19104-6323
mjoullie@sas.upenn.edu
Received J une 27, 2001
A short and efficient total synthesis of isoroquefortine C, the 3,12-(Z)-isomer of roquefortine C,
from L-tryptophan methyl ester hydrochloride and 4(5)-(hydroxy)methylimidazole hydrochloride
is described.
In tr od u ction
Roquefortine C (1) was first isolated by two indepen-
dent groups from Penicillium roqueforti Thom strain
along with several other indole compounds (roquefortines
A and B).1-4 Since its initial discovery, roquefortine C
(1) has been found in a number of other P. roqueforti
cultures,5,6 as well as in penicillium strains isolated from
a variety of food products.7-10
Isoroquefortine C (2), which has not been isolated from
nature, is the 3,12-double bond isomer of roquefortine C
(1). This compound has been obtained with complete
conversion from the natural product under photochemical
conditions (Figure 1).11
F igu r e 1. Photoisomerization of roquefortine C (1) to isoro-
quefortine C (2).
Sch em e 1a
During a study designed to establish the stereochem-
istry of the histidine double bond, Vleggaar and Wessels8
assigned the name isoroquefortine to the photoproduct
of roquefortine C. To avoid possible confusion with
isomers of other roquefortines and to establish a clear
relationship between the two isomers, we have decided
to add C to this original name.
a
Reagents and conditions: (a) 1 N HCl/MeOH, ∆; (b) 4 N
MeSO3H, 115 °C.
The existence of isoroquefortine C (2) was not noted
until 1979 when the configuration of the 3,12-double bond
of roquefortine became the focus of attention.8,11 The (E)-
configuration of the 3,12-double bond in the dehydrohis-
tidine side chain was established by comparison of
spectral properties of the two isomers,11 and also by 13C
experiments.8 The absolute configuration of roquefortine
Roquefortine C is found in the blue vein of Roquefort
and other blue cheeses and has also been detected in
other sources such as feed grain. Neurotoxic properties
were reported by Wagener et al. (paralytic activities),9
and Scott et al.3 estimated the 50% lethal dose in mice
to be 15-20 mg/kg after intraperitoneal injection. Clinical
symptoms observed in cows included extensive paralysis,
which did not respond to calcium treatment. The disease
symptoms disappeared as soon as the cows were no
longer fed moldy grain. The same symptoms were ob-
served in a human study and were linked to the presence
of roquefortine C in a contaminated commercial beer.13
However, these results could not be reproduced. Arnold
and co-workers were unable to duplicate the previously
detected activity and found the lethal dose to be 10 times
larger than reported.14 The inconsistency of these obser-
vations may be due either to the presence of an impurity
or to the presence or absence of isoroquefortine. Both
roquefortine C (1) and isoroquefortine C (2) may be
recrystallized from methanol and therefore may not be
separated by this method. Isoroquefortine C is the more
stable isomer, possibly because of the presence of a
1
C (1) was later determined by degradation and NOE H
NMR experiments (Scheme 1).12
(1) Ohmomo, S.; Sato, T.; Utagawa, T.; Abe, M. Agric. Biol. Chem.
1975, 39, 1333-1334.
(2) Scott, P. M.; Kennedy, B. P. C. J . Agric. Food Chem. 1976, 24,
865-868.
(3) Scott, P. M.; Merrien, M.-A.; Polonsky, J . Experientia 1976, 32,
140-141.
(4) Ohmomo, S.; Utagawa, S.; Abe, M. Agric. Biol. Chem. 1977, 41,
2097-2098.
(5) Scott, P. M.; Kennedy, B. P. C.; Harwig, J .; Blanchfield, B. Appl.
Environ. Microbiol. 1977, 33, 249-253.
(6) Engel, G.; Teuber, M. Eur. J . Appl. Microbiol. Biotechnol. 1978,
6, 107-111.
(7) Leistner, L.; Eckardt, C. Fleischwirtschaft 1979, 59, 1892-1896.
(8) Vleggaar, R.; Wessels, P. L. J . Chem. Soc., Chem. Commun. 1980,
160-162.
(9) Wagener, R. E.; Davis, N. D.; Diener, U. L. Appl. Environ.
Microbiol. 1980, 39, 882-887.
(10) Ohmomo, S.; Ohashi, T.; Abe, M. Agric. Biol. Chem. 1980, 44,
1929-1930.
(11) Scott, P. M.; Polonsky, J .; Merrien, M. A. J . Agric. Food. Chem.
1979, 27, 201-202.
(13) Cole, R. J .; Dorner, J . W.; Cox, R. H.; Raymond, L. W. J . Agric.
Food Chem. 1983, 31, 655-657.
(14) Arnold, D. L.; Scott, P. M.; McGuire, P. F.; Hartwig, J .; Nera,
E. A. Food Cosmet. Toxicol. 1978, 16, 369-371.
(12) Yamaguchi, T.; Nozawa, K.; Nakajima, S.; Kawai, K.; Udagawa,
S. Proc. J pn. Assoc. Mycotoxicol. 1991, 34, 29-32.
10.1021/jo0106593 CCC: $22.00 © 2002 American Chemical Society
Published on Web 10/26/2001

Total Synthesis of Isoroquefortine C
J . Org. Chem., Vol. 67, No. 3, 2002 621
Sch em e 2a
a
Reagents and conditions: (a) (Boc)2, NaOH, Bu4NHSO4,
CH2Cl2, 91%; (b) NPSP, PPTS, CH2Cl2, 78%; (c) MeOTf, tributyl(3-
methyl-2-butenyl)stannane, 2,6-di-tert-butyl-4-methylpyridine, -10
°C-∆, 69%; (d) LiOH, THF/MeOH, quantitative.
F igu r e 2. Retrosynthetic analysis of isoroquefortine (2).
Sch em e 3a
hydrogen bond between the NH of the diketopiperazine
and the sp2 nitrogen of the imidazole. As the biological
activity of this indole alkaloid has not yet been investi-
gated, isoroquefortine C is worthy of synthetic investiga-
tion in its own right.
In an attempt to clarify the biological activity profile
of these compounds, as well as to develop methods for
the stereoselective synthesis of both (E)- and (Z)-dehy-
drohistidine residues, we have undertaken the synthesis
of both isomers. We now disclose a short and efficient
total synthesis of isoroquefortine C (2).
a
Reagents and conditions: (a) benzyl carbamate, 56%; (b)
Resu lts a n d Discu ssion
MeOH/H+, 88%; (c) PCl3, P(OMe)3, 85%; (d) H2 Pd/C 5%, quantita-
tive; (e) Boc2O, 95%.
The retrosynthesis of isoroquefortine (Figure 2) begins
with disconnection of the two amide bonds of the dike-
topiperazine to provide a reverse-prenyl hexahydropyr-
roloindole and a (Z)-dehydrohistidine moiety. The former
intermediate may be prepared from tryptophan, while
the latter compound may obtained by condensation of
glycine ester derivatives with imidazole carboxaldehyde
derivatives.
Sch em e 4a
The synthesis of the reverse prenylated hexadihydro-
pyrrolo[2,3-b]indole moiety 6 was accomplished according
to the procedure of Mardsen et al.,15 starting from
L-tryptophan methyl ester hydrochloride 4 (Scheme 2).
Following protection of both the R- and side chain amino
groups of ester 4, selenylation-induced ring closure with
N-phenylselenophthalimide (NPSP)16 provided the tri-
cyclic compound 5. Displacement of the phenylselenide
was achieved by treatment with tributyl(3-methyl-2-
butenyl)stannane.17 Saponification of the ester group
provided the desired carboxylic acid 6 (Scheme 2).
The N-acyl-2-(dialkyloxyphosphinyl)glycine ester de-
rivatives 9-11 were easily prepared from glyoxylic acid
7 in three, four, and five steps, respectively, following
the procedure of Schmidt et al. (Scheme 3).18
a
Reagents and conditions: (a) PdTr: TrCl, TEA, DMF 94% or
PdONB: Na2CO3,ONBCl, DMF, 69%; (b) Dess-Martin 89-99%.
labile under relatively mild conditions (dilute TFA or Hg
lamp), appeared to be compatible with the acid-sensitive
target compound.
The three main building blocks described above were
readily prepared in large scale. The next challenge was
the isolation of dehydrohistidine derivatives to allow for
coupling with indole moiety 6. The Wittig-Horner reac-
tion between glycine ester derivatives 9 and 11 and
aldehydes 13 and 14 provided the desired protected (Z)-
dehydrohistidines (15 to 18).23,24 However, the selective
deprotection of the amine was unsuccessful. Results
varied between degradation of the starting material or
The imidazole moiety was produced from alcohol 12
via a protection/Dess-Martin oxidation sequence19,20
(Scheme 4). Both the trityl (Tr)21 and o-nitrobenzyl group
(ONB)22 were employed. These derivatives, which are
(19) Dess, D. B.; Martin, J . C. J . Am. Chem. Soc. 1991, 113, 7277-
7287.
(20) Ireland, R. E.; Liu, L. J . Org. Chem. 1993, 58, 2899.
(21) Dinsmore, C. J .; Williams, T. M.; O’Neill, T. J .; Liu, D.; Rands,
E.; Culberson, J . C.; Lobell, R. B.; Koblan, K. S.; Kohl, N. E.; Gibbs, J .
B.; Oliff, A. I. Bioorg. Med. Chem. Lett. 1999, 23, 3301-3306.
(22) Antonini, I. C., G.; Franchetti, P.; Grifantini, M.; Martelli, S.
Synthesis 1983, 47-49.
(23) Schmidt, U.; Griesser, H.; Leitenberger, V.; Lieberknecht, A.;
Mangold, R.; Meyer, R.; Riedl, B. Synthesis 1992, 487-489.
(24) Oba, M.; Ueno, R.; Fukuoka, M.; Kainosho, M.; Nishiyama, K.
J . Chem. Soc., Perkin Trans. 1 1995, 1603-1609.
(15) Marsden, S. P.; Depew, K. M.; Danishefsky, S. J . J . Am. Chem.
Soc. 1994, 116, 11143-11144.
(16) Nicolaou, K. C.; Claremon, D. A.; Barnette, W. E.; Seitz, S. P.
Tetrahedron 1985, 41, 4835-4841.
(17) Engler, T. A.; Reddy, J . P.; Combrink, K. D.; Vander Velde, D.
J . Org. Chem. 1990, 55, 1248-1254.
(18) Schmidt, U.; Lieberknecht, A.; Wild, J . Synthesis 1984, 53-
60.

622 J . Org. Chem., Vol. 67, No. 3, 2002
Schiavi et al.
Sch em e 5
Sch em e 6
isolation of the fully deprotected compound, which proved
extremely unstable and not suitable for further reaction
(Scheme 5).
an o-nitrobenzyl-protected imidazole in 55% yield. At-
tempts to carry out the same reaction with a trityl-
protected imidazole failed. The intermediate was ob-
served on TLC, but isolation was unsuccessful presumably
due to its instability during the workup sequence. It is
interesting to note that only one intermediate was
observed during the course of this reaction, the tetracyclic
compound protected on the indole nitrogen. Deprotection
was completed by treatment of this intermediate with
silica. A similar deprotection of aromatic amino-Boc
groups in the presence of silica has been reported.29
Indole-containing compounds related to carboxylic acid
6 have been known to exhibit interesting NMR proper-
ties.15 The aromatic proton in position 7 (see Figure 2)
generally appears either as a broad or weak signal.
Compounds 19-21 showed similar spectral characteris-
tics. However, after formation of the fourth ring, the four
protons were clearly visible in the expected aromatic
range. It is believed that this behavior is the result of a
change in hybridization of one or more atoms in the
polycyclic compound.
As a final step, the imidazole was successfully depro-
tected using photochemical conditions (mercury lamp
irradiation) to yield isoroquefortine C in good yield. The
chemical shift of the H12 proton was found at 6.67 ppm
in contrast with the 6.35 ppm value reported for the same
proton in roquefortine C (1).11 Chemical shifts for C12,
C17, and C3, which are different from those exhibited by
1, were found at the following positions: 137.85 ppm for
C3 (122.30 for 1), 117.65-105.45 ppm for C12-C17 (110.90-
134.30 ppm for 1), in agreement with previously reported
values.8
To overcome this problem, an alternative coupling
strategy was investigated (Scheme 6). The acid 6 was first
coupled with the free amine 10 in the presence of DCC
and HOBT to give the glycine ester derivative 19 as a
mixture of diastereomers in excellent yield (93%). Alde-
hydes 13 and 14 were condensed with phosphonate 19
in the presence of DBU to give linear compounds 20 and
21 in 67% and 79% yield, respectively.
1
Product 21 possessed unusual characteristics in its H
NMR spectrum. The proton resonances corresponding to
positions 12 and 17 (see Figure 2) were not observed
initially. Low-temperature spectra exhibited poor resolu-
tion and indicated the presence of a number of rotamers.
High-temperature experiments, however, led to the ap-
pearance of H12 and H17 as two broad signals, with
chemical shifts similar to those of the corresponding H12
and H17 of compound 20.
Formation of the fourth ring was envisioned as a two-
step sequence: deprotection of tert-butoxycarbonyl groups,
followed by cyclization under classical basic conditions
in a manner analogous to our previously reported syn-
thesis of roquefortine D.25 Unfortunately, the use of
trifluoroacetic acid in dichloromethane led only to deg-
radation of starting material. Use of other acidic condi-
tions proved equally unsuccessful. Attempts were then
made to activate the ester and trap the free amine
intermediate in a one-step reaction. Use of TMSCl/
PhOH,26 TMSOTf/2,6-lutidine,27 or ZnBr2 led to the
28
recovery of starting material. However, we were gratified
to discover that use of TMSI (prepared from hexameth-
yldisilane/I2) in acetonitrile afforded compound 23 with
Con clu sion
Isoroquefortine C (2) was synthesized for the first time
in eight linear steps from L-tryptophan methyl ester
(25) Chen, W. C.; J oullie´, M. M. Tetrahedron Lett. 1998, 39, 8401-
8404.
(26) Keiser Sr, E.; Picart, F.; Kubiak, T.; Tam, J . P.; Merrifield, R.
B. J . Org. Chem 1993, 58, 5167.
(27) Xiao, D.; East, S. P.; J oullie´, M. M. Tetrahedron Lett. 1998, 39,
9631-9632.
(28) Nigam, S. C.; Mann, A.; Taddei, M.; Wermuth, C. G. Synth.
Commun. 1989, 19, 3139-3142.
(29) Apelqvist, T.; Wensbo, D. Tetrahedron Lett. 1996, 37, 1471-
1472.

Total Synthesis of Isoroquefortine C
J . Org. Chem., Vol. 67, No. 3, 2002 623
Rf: 0.6 (5/95 MeOH/CH2Cl2). IR (CHCl3): 1721, 1650, 1446,
748-701 cm-1. 1H NMR (500 MHz, CDCl3) δ: 9.33 (s, 1H, NH),
7.49 (s, 1H, H15), 7.35 (m, 9H, Tr), 7.14 (m, 6H, Tr), 6.88 (s,
1H, H17), 6.38 (s, 1H, H12), 3.81 (s, 3H, CH3 ester), 1.47 (s, 9H,
Boc). 13C NMR (125 MHz, CDCl3) δ: 166.55 (CdO ester),
153.70 (CdO carbamate), 142.40 (Tr), 139.30 (C15), 137.40
(C13), 130.15 (Tr), 128.70 (Tr), 128.60 (Tr), 127.95 (C3), 123.05
(C17), 111.50 (C12), 80.80 (Boc), 75.70 (Tr), 52.50 (CH3 ester),
hydrochloride in an overall yield of 16%. The three
fragments (6, 9 or 11, 3 or 4) necessary to perform this
synthesis were easily prepared in large scale, allowing
for preparation of quantities of isoroquefortine C (2)
suitable for biological testing.
Exp er im en ta l Section
28.60 (Boc). HRMS (EI): m/z calcd for
C31H32N3O4 and
Gen er a l Meth od s. Reactions requiring air-sensitive ma-
nipulations were conducted under an argon atmosphere.
Methylene chloride was distilled from calcium hydride, and
tetrahydrofuran, diethyl ether, and hexane were distilled from
sodium/benzophenone. Analytical TLC was performed on 0.25
mm E. Merck silica gel 60 F254 plates. Merck silica gel (60,
particle size 0.040-0.063 mm) was used for flash column
chromatography. NMR spectra were recorded on Bruker AMX-
500 spectrometers and calibrated by using residual undeuter-
ated solvent as an internal reference. Chemical shifts (δ) were
measured in parts per million, and coupling constants (J
values) are in hertz (Hz). Infrared spectra (IR) were recorded
on a Perkin-Elmer 1600 series FT-IR spectrometer. High-
resolution mass spectra (HRMS) were recorded on a Micromass
AutoSpec spectrometer using electron impact (EI). Optical
rotations were recorded on a Perkin-Elmer model 341 pola-
rimeter at the sodium D line.
C
31H31N3O4Na 509.2315 and 532.2212, found 510.2377 and
532.2204. Product 16 was isolated in 89% yield (80 mg).
3-(1-(o-Nitr oben zyl)-1H-im id a zol-4-yl)-2-ben zyloxyca r -
bon yla m in oa cr ylic Acid Meth yl Ester 17. C22H20N4O6.
White solid. Rf: 0.25 (5/95 MeOH/CH2Cl2). IR (CHCl3): 1721,
1649, 1527, 1223, 860-750 cm-1. H NMR (500 MHz, CDCl3)
1
δ: 9.58 (s, 1H, NH), 8.17 (dd, J ) 1, 8 Hz, ONB), 7.64 (m, 1H,
ONB), 7.62 (s, 1H, H17), 7.58 (m, 1H, ONB), 7.50-7.30 (m, 5H,
Z), 7.05 (s, 1H, H15), 6.90 (dd, J ) 1, 8 Hz, ONB), 6.57 (s, 1H,
H
12), 5.54 (s, 2H, ONB), 5.18 (s, 2H, Z), 3.80 (s, 3H, CH3 ester).
13C NMR (125 MHz, CDCl3) δ: 166.10 (CdO ester), 154.50 (Cd
O carbamate), 147.60 (ONB), 138.85 (Z), 138.30 (C15), 136.65
(C13), 134.90 (ONB), 132.20 (ONB), 129.95 (ONB), 129.43
(ONB), 128.85 (ONB), 128.60 (Z), 128.50 (Z), 127.90 (Z), 126.00
(C3), 121.15 (C17), 112.65 (C12), 67.65 (Z), 52.70 (CH3 ester),
48.65 (ONB). HRMS (EI): m/z calcd for C22H20N4O6Na 459.1280,
found 459.1272. Product 17 was isolated in 82% yield (75 mg).
3-(1-(o-Nit r ob en zyl)-1H -im id a zol-4-yl)-2-ter t-b u t oxy-
ca r bon yla m in oa cr ylic Acid Meth yl Ester 18. C19H22N4O6.
White solid. Rf: 0.15 (5/95 MeOH/CH2Cl2). IR (CHCl3): 1714,
1640, 1529, 755-729 cm-1. 1H NMR (500 MHz, CDCl3) δ: 8.24
(d, J ) 8 Hz, 1H, ONB), 7.66 (s, 1H, H15), 7.60 (m, 1H, ONB),
7.53 (m, 1H, ONB), 6.88 (s, 1H, H17), 6.71 (d, J ) 8 Hz, 1H,
ONB), 6.21 (s, 1H, H12), 5.69 (s, 2H, ONB), 3.77 (s, 3H, CH3
ester), 1.47 (s, 9H, Boc). 13C NMR (125 MHz, CDCl3) δ: 165.60
(CdO ester), 152.75 (CdO carbamate), 147.20 (ONB), 140.25
(C15), 136.20 (C13), 134.30 (ONB), 132.40 (ONB), 129.60 (ONB),
128.45 (ONB), 127.95 (C3), 126.00 (C17), 115.80 (C12), 81.75
(Boc), 53.00 (CH3 ester), 46.55 (ONB), 28.60 (Boc). HRMS
(EI): m/z calcd for C19H23N4O6 403.1617, found 403.1622.
Product 18 was isolated in 85% yield (65 mg).
Products 4-6 were prepared following the procedure of
Mardsen et al.15 Products 7-11 were prepared following the
procedure of Schmidt et al.18
1-Tr ityl-1H-im id a zole-4-ca r ba ld eh yd e 13 a n d 1-(2-Ni-
tr oben zyl)-1H-im id a zole-4-ca r ba ld eh yd e 14. Protection of
4(5)-hydroxymethylimidazole 12 was done according to the
procedure of Dinsmore et al.21 for the trityl group and Antonin
et al.22 for the o-nitrobenzyl group. The oxidation step was
reported with manganese dioxide in dioxane with 80-95%
yield30,31 for compound 13 and 24-48% yield for 14.22 Yields
were improved to 99% for 13 and 89% for 14 using the Dess-
Martin reagent.19,20 The physical data for all compounds were
identical to those reported in the literature.
Gen er a l P r oced u r e for th e Hor n er -Wa d sw or th -Em -
m on s Rea ction . The phosphonate (1 equiv) was dissolved in
CH2Cl2 (1 mL/0.05 mmol) and placed in an ice bath at 0 °C.
The solution was treated with DBU (2 equiv) and stirred at
the same temperature for 10 min. The aldehyde (1.6 equiv) in
CH2Cl2 (0.1 mmol/mL) was then added to the solution. The
mixture was allowed to warm to room temperature and was
stirred overnight. The yellow solution was then washed with
1 N HCl, saturated NaHCO3, and brine. The organic layer was
dried over MgSO4, filtered, and concentrated under reduced
pressure to yield a yellow foam. Flash chromatography, eluting
with ether for tryptophan derivatives and 1% methanol/CH2-
Cl2 for dehydrohistidine derivatives, yielded the products as
a white foam.
2-Ben zyloxyca r bon yla m in o-3-(1-tr ityl-1H-im id a zol-4-
yl)a cr ylic Acid Meth yl Ester 15. C34H29N3O4. White solid.
Rf: 0.65 (5/95 MeOH/CH2Cl2). IR (CHCl3): 1724, 1652, 1542,
750-700 cm-1. 1H NMR (500 MHz, CDCl3) δ: 9.71 (s, 1H, NH),
7.51 (s, 1H, H15), 7.40-7.30 (m, 14H, Tr + Z), 7.16-7.13 (m,
6H, Tr), 6.93 (s, 1H, H17), 6.51 (s, 1H, H12), 5.18 (s, 2H, Z),
3.80 (CH3 ester). 13C NMR (125 MHz, CDCl3) δ: 166.10 (CdO
ester), 154.50 (CdO carbamate), 142.30 (Tr), 139.35 (C17),
137.10 (Z), 136.70 (C13), 130.10 (Tr), 128.80 (Z), 128.70 (Tr),
128.65 (Tr), 128.60 (Z), 128.40 (Z), 127.65 (C3), 123.35 (C17),
112.70 (C12), 76.20 (Tr), 67.60 (Z), 52.60 (CH3 ester). HRMS
(EI): m/z calcd for C34H30N3O4 and C34H29N3O4Na 544.2236
and 566.2055, found 544.2251 and 566.2076. Product 15 was
isolated in 62% yield (401 mg).
3a-(1,1-Dim eth ylallyl)-2-[1-m eth oxycar bon yl-2-(1-tr ityl-
1H-im id a zol-4-yl)vin ylca r ba m oyl]-2,3,3a ,8a -tetr a h yd r o-
p yr r olo[2,3-b]in d ole-1,8-d ica r boxylic Acid Di-ter t-bu tyl
Ester 20. C52H57N5O7. White solid. Rf: 0.4 (95/5 CH2Cl2/
MeOH). IR (CHCl3): 2976, 1715, 1708 cm-1. [R]20D: -43 (c 0.9,
CHCl3). 1H NMR (500 MHz, CDCl3) δ: 7.52 (s, 1H, H17), 7.38-
7.32 (m, 9H, Tr), 7.24 (t, J ) 7.7 Hz, 1H, Ph), 7.17 (d, J ) 7.4
Hz, 1H, Ph), 7.12 (m, 5H, trityl), 7.04 (t, J ) 8 Hz, 1H, Ph),
6.88 (s, 1H, H15), 6.34 (s, 1H, H5a), 6.23 (s, 1H, H12), 5.85 (dd,
J ) 10.8, 17.3 Hz, 1H, H19), 4.96 (m, 2H, H20), 3.83 (m, 1H,
H
H
11a), 3.80 (s, 3H, CH3 ester), 2.49 (dd, J ) 7, 12.8 Hz, 1H,
11), 2.45 (dd, J ) 9.9, 12.8 Hz, 1H, H11), 1.51 (s. 9H, Boc),
1.26 (s, 9H, Boc), 1.01 (s, 3H, H22), 0.94 (s, 3H, H21). 13C NMR
(125 MHz, CDCl3) δ: 169.95 (C4), 159.85 (C1), 152.30 (Boc),
143.45 (C19), 142.95 (C6a), 141.95 (Tr), 138.95 (C15), 136.50 (C3),
133.50 (C10a), 129.75 (Tr), 128.45 (C8), 128.35 (Tr) 128.25 (Tr),
127.40 (C13), 124.75 (C10), 122.75 (C9), 122.50 (C17) 114.00 (C20),
111.10 (C12), 81.45 (Boc), 81.05 (Boc), 79.25 (C5a), 75.75 (Tr),
61.80 (C11a), 60.90 (C10a), 52.10 (MeO), 40.45 (C18), 35.70 (C11),
28.35 (Boc), 28.05 (Boc), 23.05 (C21), 22.35 (C22). HRMS (EI):
m/z calcd for C52H58N5O7 864.4336, found 864.4344. Product
20 was isolated in 67% yield.
2-[2-(1-(o-Nitr oben zyl-1H-im id a zol-4-yl)-1-m eth oxyca r -
b on ylvin ylca r b a m oyl]-3a -(1,1-d im et h yla llyl)-2,3,3a ,8a -
tetr a h yd r op yr r olo[2,3-b]in d ole-1,8-d ica r boxylic Acid Di-
ter t-bu tyl Ester 21. C40H48N6O9. White solid. Rf: 0.4 (95/5
CH2Cl2/MeOH). IR (CHCl3): 1712, 1529, 1344, 1154 cm-1
.
[R]20D -46 (c 0.85, CHCl3). 1H NMR (500 MHz, CDCl3) δ: 8.14
(dd, J ) 1.3, 8.1 Hz, 1H, ONB), 7.65 (s, 1H, H15), 7.60 (dt, J )
1.3, 8.1 Hz, 1H, ONB), 7.51 (m, 1H, ONB), 7.25 (m, 1H, Ph),
7.21 (m, 1H, Ph), 7.14 (s, br, 1H, H17), 7.05 (dt, J ) 1, 7.5 Hz,
1H,), 6.96 (d, J ) 7.8 Hz, 1H, ONB), 6.51 (s, br, 1H, H12), 6.29
(s, 1H, H5a), 5.88 (dd, J ) 10.8, 17.3 Hz, 1H, H20), 5.55 (s, 2H,
ONB), 5.01 (dd, J ) 1, 10.8 Hz, 1H, H19), 4.98 (dd, J ) 1, 17.3
Hz, 1H, H19), 3.85 (dd, J ) 7.2, 9.6 Hz, 1H, H11a), 3.80 (s, 3H,
2-ter t-Bu toxyca r bon yla m in o-3-(1-tr ityl-1H-im id a zol-4-
yl)a cr ylic Acid Meth yl Ester 16. C31H31N3O4. White solid.
(30) Hunt, J . T.; Lee, V. G.; Leftheris, K.; Seizinger, B.; Carboni, J .;
Mabus, J .; Ricca, N. Y.; Veeraswamy, M. J . Med. Chem. 1996, 39, 353-
358.
(31) Lee, K. J .; J oo, K. C.; Kim, E. J .; Lee, M.; Kim, D. H. Bioorg.
Med. Chem. 1997, 5, 1989-1998.

624 J . Org. Chem., Vol. 67, No. 3, 2002
Schiavi et al.
CH3 ester), 2.53 (dd, J ) 7.1, 12.9 Hz, 1H, H11), 2.48 (dd, J )
9.7, 12.9 Hz, 1H, H11). 13C NMR (125 MHz, CDCl3) δ: 171.20
(C3), 166.10 (C1), 152.65 (Boc), 147.50 (ONB), 143.60 (C19),
143.15 (C6a), 138.60 (C2), 138.15 (C15), 134.80 (ONB), 134.30
(C10a), 132.20 (ONB), 129.80 (C8), 129.40 (ONB), 128.70 (C9),
125.85 (ONB), 125.80 (C13), 125.15 (C10), 123.30 (ONB), 121.15
(C17), 118.30 (C1), 114.35 (C20), 110.90 (C12), 81.55-80.85 (Boc),
79.50 (C5a), 62.10 (C10b), 61.40 (C11a), 52.60 (CH3 ester), 48.50
(ONB), 40.70 (C18), 35.85 (C11), 28.65-28.30 (Boc), 23.30-22.60
(C21-C22). HRMS (EI): m/z calcd for C40H48N6O9Na 779.3380,
found 779.3383. Product 21 was isolated in 79% yield (298 mg).
2-[[(Dim eth oxyp h osp h or yl)m eth oxyca r bon ylm eth yl]-
ca r ba m oyl]-3a -(1,1-d im eth yla llyl)-2,3,3a ,8a -tetr a h yd r o-
p yr r olo[2,3-b]in d ole-1,8-d ica r boxylic Acid Di-ter t-bu tyl
Ester 19. To a solution of 6 (320 mg, 0.68 mmol) in dichlo-
romethane (20 mL) were added DCC (182 mg, 0.88 mmol),
HOBT (110 mg, 0.81 mmol), and 10 (270 mg, 1.36 mmol). The
mixture was stirred at room temperature for 12 h and diluted
with ether (50 mL). The DCU was removed by filtration and
the organic layer washed with 1 N HCl, saturated NaHCO3,
and brine. The organic layer was dried over MgSO4, filtered,
and concentrated under reduced pressure to yield a light
yellow foam. Flash chromatography, eluting with 1% methanol/
CH2Cl2, yielded the product as a white foam (410 mg, 93%).
and stirred at room temperature overnight, and solvent was
then removed by filtration. The silica was washed with a 10%
methanol/CH2Cl2 solution. The organic layers were distilled
under reduced pressure, and the residue was then recrystal-
lized from methanol to give the cyclic compound. Product 23
was isolated in 55% yield (45 mg). C29H28N6O4. White solid.
Rf: 0.8 (95/5 CH2Cl2/MeOH). IR (CHCl3): 1731, 1688, 1630
cm-1. [R]20 -307 (c 0.7, EtOH). 1H NMR (500 MHz, CDCl3)
D
δ: 11.46 (s, br, NH), 8.20 (dd, J ) 1, 8.2 Hz, 1H, H26), 7.66 (m,
1H, H27), 7.64 (s, 1H, H15), 7.57 (m, 1H, H28), 7.19 (d, J ) 7.4
Hz, H10), 7.12 (m, 1H, H9), 7.08 (s, 1H, H17), 6.92 (d, J ) 7.7
Hz, 1H, H29), 6.78 (pseudo t, J ) 7 Hz, 1H, H8), 6.68 (s, 1H,
H
12), 6.61 (d, J ) 7.8 Hz, 1H, H7), 6.02 (dd, J ) 10.8, 17.4 Hz,
1H, H19), 5.69 (s, 1H, H5a), 5.59 (s, 2H, H23), 5.15 (dd, J ) 1,
11 Hz, H20), 5.12 (dd, J ) 1, 17.4 Hz, 1H, H20), 5.00 (s, br,
NH), 4.14 (dd, J ) 5.8, 11.5 Hz, H11a), 2.63 (dd, J ) 5.8, 12.3
Hz, 1H, H11), 2.50 (pseudo t, J ) 11.9 Hz, 1H, H11), 1.18 (s,
3H, H21), 1.08 (s, 3H, H22). 13C NMR (125 MHz, CDCl3) δ:
165.80 (C1), 158.60 (C4), 150.85 (C6a), 147.60 (C24), 144 (C19),
139.20 (C29), 138.35 (C15), 134.90 (C17), 130.00 (C28), 129.35
(C27), 129.30 (C26), 129.25 (C8), 127.60 (C10a), 126.05 (C13),
125.60 (C10), 121.10 (C3), 119.10 (C9), 114.85 (C20), 109.30 (C12),
104.65 (C7), 78.40 (C5a), 62.00 (C10b), 59.50 (C11a), 48.70 (C23),
41.35 (C18), 37.65 (C11), 23.4 (C21), 22.90 (C22). HRMS (EI): m/z
calcd for C29H28N6O4Na 547.2069, found 547.2091.
C
31H46N3O10P. Rf: 0.5 (95/5 CH2Cl2/MeOH). IR (CHCl3): 2976,
1749, 1714 cm-1. [R]20 -36 (c 0.45, EtOH). 1H NMR (500
D
Isor oqu efor tin e C or 10b-(1,1-Dim eth yla llyl)-3-(3H-
im idazol-4-ylm eth ylen e)-2,3,6,10b,11,11a-h exah ydr o-5aH-
p yr a zin o[1′,2′:1,5]p yr r olo[2,3-b]in d ole-1,4-d ion e 2. A so-
lution of 23 (20 mg) in 1,4-dioxane (40 mL) was placed in a
quartz immersion cell. A stream of nitrogen was introduced
into the solution while it was irradiated with a mercury vapor
lamp with a Pyrex filter (450-W). The photolysis was complete
after 1.5 h. The solvent was then removed under reduced
pressure and the residue was recrystallized from methanol to
give 2 in 81% yield (12 mg). C22H23N5O2. White solid. Rf: 0.1
(90/10 CH2Cl2/MeOH + ammonia vapors). IR (CHCl3): 1680,
MHz, CDCl3) δ: 7.27 (t, J ) 7.7 Hz, 1H, Ph), 7.20 (d, J ) 7.5
Hz, 1H, Ph), 7.09 (t, J ) 7.5 Hz, 1H, Ph), 6.47 (d, J ) 8.9 Hz,
1H, NH), 6.18 (d, J ) 7 Hz, H5a), 5.89-5.93 (m, 1H, H19), 5.20-
5.27 (m, 1H, H3), 5.10 (dd, J ) 7.6, 10.8 Hz, H20), 5.03 (dd, J
) 3.6, 17.3 Hz, H20), 3.75-3.90 (m, 4H, H11a+CH3 ester), 2.43-
2.48 (m, 1H, H11), 2.31-2.38 (m, 1H, H11), 1.58 (s, 9H, Boc),
1.45 (s, 9H, Boc), 1.07-1.06-0.99-0.98 (4s, 4*3H, CH3 prenyl).
13C NMR (125 MHz, CDCl3) δ: 172.20-171.90 (CdO ester),
167.25-167.20 (CdO amide), 152.75 (CdO carbamate), 143.60-
143.55 (C19), 143.20 (C6a), 134.00 (C10a), 128.90 (C10), 125.20
(C9), 123.75 (C8), 118.62 (br; C7), 114.75 (C20), 81.90-81.60
(Boc), 79.60-79.40 (C5a), 66.20 (C10b), 61.60-61.50 (C11a),
54.65-54.60-54.55-54.50 (POCH3), 54.30-54.25-54.20-
54.15 (POCH3), 53.65-53.60 (CH3 ester), 50.80-50.70-49.60-
49.55 (C3), 40.70-40.75 (C18), 35.60-35.45 (C11), 28.80-28.65-
28.60 (Boc), 23.35-23.30-22.55 (CH3 prenyl). HRMS (EI): m/z
calcd for C31H46N3O10NaP 674.2816, found 674.2827. Product
19 was isolated in 67% yield (415 mg).
1630 cm-1 (lit.11 IR 1676, 1627 cm-1). [R]20 -390 (c 0.05,
D
CHCl3) (lit.11 [R]D -409 (c 0.071, CHCl3)). 1H NMR (500 MHz,
CDCl3) δ: 11.66 (s, br, 1H, NH), 10.03 (s, br, 1H, NH), 7.68 (s,
br, 1H, H15), 7.18 (m, 1H, H10), 7.10 (t, J ) 7.5 Hz, 1H, H9),
7.08 (s, 1H, H17), 6.76 (t, J ) 7.5 Hz, 1H, H8), 6.71 (s, 1H, H12),
6.59 (d, J ) 7.8 Hz, 1H, H7), 6.00 (dd, J ) 10.8, 17.3 Hz, 1H,
H
19), 5.67 (s, 1H, H5a), 5.11 (m, 2H, H20), 4.97 (s, br, 1H, NH),
4.12 (dd, J ) 5.6, 11.6 Hz, 1H, H11a), 2.60 (dd, J ) 6, 12.2 Hz,
1H, H11), 2.49 (m, 1H, H11), 1.15-1.04 (H21-H22). 13C NMR
(125 MHz, CDCl3) δ: 167.00 (C1), 158.85 (C4), 150.75 (C6a),
144.00 (C19), 137.85 (C3), 135.65 (C15), 129.35 (C8), 129.25 (C10a),
127.00 (C13), 125.65 (C10), 119.25 (C9), 117.65 (C17), 114.90 (C20),
109.35 (C7), 105.45 (C12), 78.40 (C5a), 62.00 (C10b), 59.50 (C11a),
41.35 (C18), 37.65 (C11), 23.00-22.50 (C21-C22). HRMS (EI):
m/z calcd for C22H24N5O2 390.1930, found 390.1956.
3-(3-(o-Nitr oben zyl)-3H-im id a zol-4-ylm eth ylen e)-10b-
(1,1-dim eth ylallyl)-2,3,6,10b,11,11a-h exah ydr o-5a H-pyr azi-
n o[1′,2′:1,5]p yr r olo[2,3-b]in d ole-1,4-d ion e 23. The TMSI
solution was prepared by dissolving freshly sublimed iodine
(5 equiv) in CH2Cl2 (1 mL/70 mg) under a nitrogen atmosphere
and adding hexamethyldisilane (7.5 equiv). The solution was
heated at 70 °C (bath temperature) until disappearance of the
purple color gave way to a pale yellow solution. The solution
was allowed to warm to room temperature under a nitrogen
atmosphere and was used immediately. The protected linear
compound (1 equiv) was dissolved in freshly distilled acetoni-
trile (0.023 mmol/mL), cooled in an ice bath under a nitrogen
atmosphere, and treated with the TMSI solution. The mixture
was then stirred for 45 min at 0 °C or until the TLC showed
the disappearance of starting material. The reaction was
warmed to room temperature and quenched with saturated
NaHCO3 (0.04 mmol/mL). The organic layer was dried over
MgSO4 and filtered. The organic layer was treated with silica
Ack n ow led gm en t. We gratefully acknowledge the
NSF (CHE 99-01449) and the University of Pennsylva-
nia for financial support.
Su p p or t in g In for m a t ion Ava ila b le: 1H NMR and 13C
NMR of compounds 15-21, 23, and 2. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O0106593