Synthesis of perfragilin A, B and some analogues

Article abstract of DOI:10.1016/S0040-4020(02)01591-0

Synthesis of the cytotoxic isoquinoline quinone perfragilin A, an improved synthesis of perfragilin B and preparation of some analogues of both these compounds are described. Cytotoxicity evaluation of a number of the products is reported. The regioselectivity in Diels-Alder reactions of differently substituted benzoquinones with 2-aza-1,3-bis(t-butyldimethylsilyloxy)-1,3-butadiene is described.

Full text of DOI:10.1016/S0040-4020(02)01591-0

Tetrahedron 59 (2003) 1349–1357
Synthesis of perfragilin A, B and some analogues
c
Vitor F. Ferreira,a Aeri Park,b Francis J. Schmitzb and Fred A. Valeriote
,
*
a
´
ˆ
´
Departamento de Quımica Organica, Universidade Federal Fluminense, Niteroi, Rio de Janeiro CEP 24020-150, Brazil
bDepartment of Chemistry and Biochemistry, The University of Oklahoma, Norman, OK, 73019-0370, USA
cJosephine Ford Cancer Center, One Ford Place, 1-D, Detroit, MI 48202, USA
Received 30 September 2002; revised 3 December 2002; accepted 3 December 2002
Abstract—Synthesis of the cytotoxic isoquinoline quinone perfragilin A, an improved synthesis of perfragilin B and preparation of some
analogues of both these compounds are described. Cytotoxicity evaluation of a number of the products is reported. The regioselectivity
in Diels–Alder reactions of differently substituted benzoquinones with 2-aza-1,3-bis(t-butyldimethylsilyloxy)-1,3-butadiene is
described. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
(2) for biological evaluation, we undertook a study to
improve yields of individual steps and possibly shorten the
synthesis of this compound, to prepare some analogues, and
to synthesize the related perfragilin A (1).
Perfragilin A (1) and B (2) belong to a small class of marine
metabolites having an isoquinoline quinone skeleton. These
compounds were isolated by our group from the bryozoan
Membranipora perfragilis1,2 and their structures fully
assigned based on NMR and X-ray data.3 The isoquinoline
quinone skeleton is also found in a few other marine
metabolites such as mimosamycin (3) isolated from several
sponges, e.g. Reniera sp4,5, Xestopongia caycedoi6 and
cribrostatin 2 (4) isolated from a Cribrochalina sp7 sponge.
Perfragilin A and B were toxic to murine leukemia cells
(P388), with perfragilin B being the more potent, ED50 0.8
and 0.07 mg/mL, respectively. Perfragilin B (1) showed
some selectivity for renal and breast cancer cells in the NCI
human tumor cell panel.8
2. Results and discussion
The synthesis of perfragilin B (2) following the general
route described earlier is outlined in Scheme 1. 2,3-Di-
chloro-1,4-benzoquinone (5) was prepared from 1,4-benzo-
quinone via the procedure described by Norris.13 Repro-
ducibility and substantial improvement in yield in this
synthesis were achieved by using a modified procedure for
preparing 5,6-dichlorocyclohexen-2-ene-1,4-dione.14 Reac-
tion of 5 with cyclopentadiene produced 6 in quantitative
yield. Replacement of the chlorines by thiomethoxy groups
was achieved in our earlier work and by others15 in
moderate to good yields (maximum reported 80%) by
carefully controlling the pH of reaction mixture. In our
current work we found that under phase transfer catalysis
conditions, 6 reacted with sodium thiomethoxide very
rapidly and the desired product 7 was obtained in
quantitative yield. Not only is the reaction rapid under
these conditions, but the product is not exposed to protic,
basic (or buffered) conditions which facilitate enolization
of 7 to its hydroquinone form, thereby lowering the yield.
The retro Diels–Alder reaction of 7 carried out at high
temperature and low pressure yielded 2,3-di-(thiomethoxy)-
1,4-benzoquinone (8) which, without purification, was
reacted with 2-aza-1,3-bis-(t-butyldimethylsilyloxy)-1,3-
butadiene (9)16 in refluxing benzene. The hot reaction
mixture was quenched with concentrated HCl to produce the
isoquinoline quinone 10 in 63% yield from 7. N-Methyl-
ation of 10 was previously carried out in DMF promoted
by tris-(3,6-dioxaoctyl)-amine (TDA-1)17 as phase transfer
catalyst. This procedure gave good yields in the synthesis of
Sometime ago we described briefly a total synthesis for
perfragilin B (2) in 3.6% overall yield from benzoquinone.9
A key step in constructing the isoquinoline quinone skeleton
was a hetero Diels–Alder reaction as had previously
been used in the syntheses of amphimedine10 and
mimosamycin.11,12 In order to obtain more perfragilin B
Keywords: synthesis; cytotoxicity; antitumor; Diels–Alder; regio-
selectivity; quinones; isoquinoline.
*
Corresponding author. Tel.: þ1-405-325-5581; fax: þ1-405-325-6111;
e-mail: fjschmitz@ou.edu
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)01591-0

1350
V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
Scheme 1.
mimomycin,11 but only moderate yield in the synthesis of
perfragilin B (2).9 In the current work we found that using
DMSO as solvent resulted in conversion of 10 to 2 in 75%
yield. The N-butyl (11) and N-benzyl (12) analogues of
perfragilin B (2), respectively, were obtained in 83 and 79%
yield from 10 using DMSO/K2CO3/TDA-1 and butyl iodide
and benzyl chloride, respectively. Use of n-butyl chloride in
DMF gave rise to different products, see Scheme 2 below.
(51% yield), the side products 13–15 were isolated in 9, 17,
and 15%, respectively (Scheme 3). The latter two
unexpected products revealed operation of a highly
regioselective Michael reaction that could be taken
advantage of to synthesize perfragilin A (1). Product 13
was identified by high resolution mass and NMR data (loss
of the d 7.08 ppm singlet characteristic of H-4 and presence
of an additional S-methyl singlet d H/C 2.66:18.0). Products
14 and 15 likewise were identified by mass (high resolution
only for 15) and NMR data [loss of one SMe signal and
replacement by signals for –NMe2 (d 3.26) and –NHMe (d
3.48)], respectively. The assigned regiochemistry of the
A detailed analysis of the reaction mixture from methylation
of 10 in DMF was carried out in hopes of determining the
cause of the low yield of the desired product. In addition to 2
Scheme 2.
Scheme 3.

V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
1351
Scheme 4.
quinone substituents was not proven by spectroscopic
methods, but can be rationalized on electronic grounds,
and was confirmed by the synthesis of perfragilin A (1), see
below. The C-5 carbonyl should be more electrophilic than
C-8 since the former is cross-conjugated with two other a,b-
unsaturated carbonyl systems while the latter is part of a
conjugated enamino ketone system. Hence Michael addition
at C-7 should be preferred. Decomposition of DMF by base
and heat18 is assumed to generate the methyl- and
dimethylamine needed to form these products. Dimethyl-
formamide had been carefully purified18 and NMR analysis
of the solvent confirmed its purity. The origin of 13 is more
obscure, but may involve Michael addition at C-4 by
thiomethoxide (released in formation of 14/15) followed by
air oxidation to give back the conjugated system of 13.
many other side products which were not individually
separated. Synthetic and natural 1 exhibited the same TLC
behavior and identical proton NMR spectra. Preparation
of 1 by this route confirms the regiochemistry of products
14–17. The N-benzyl analogue of perfragilin A, 19, was
prepared in 29% yield by reaction of 2 with benzylamine in
CH2Cl2 (Scheme 4). Selective and facile displacement of
the thiomethoxy group suggests that 2 may a biogenetic
precursor of 1.
1
All the synthetic compounds gave sharp, clean H NMR
spectra. However all the compounds containing a 7-NH2 or
7-NHR group gave very weak (broad) 13C NMR signals for
the –SMe group and many of the signals for C’s -5 to 9 were
also weak or not observed. It is possible that this is due to the
presence of a radical in this conjugated compound as has
been reported in some other cases.19
Reaction of 10 with n-butyl chloride in DMF with
K2CO3/TDA-1 gave no detectable amounts of the desired
product 11, but instead products 16–18 were isolated in 33,
11, and 5% yield, respectively, see Scheme 3. The structures
of 16 and 17 were established by mass spectral analysis and
comparison of their NMR data with that of 14 and 15. The
structure of 18 was deduced by comparison of its proton
NMR data with that of 11. The lower field shifts of the
signals H-1, H-4, and the CH2O of the butyl ether argue for
the O-alkylated structure for 18.
The synthesis of perfragilin B (2) could perhaps be
shortened if quinone 5 would undergo a Diels–Alder
reaction directly with azadiene 9 to give an isoquinoline
quinone analogous to 10, but with chlorines in place of
thiomethoxy groups. Methylation of such an intermediate
followed by displacement of the chlorines with appropriate
nucleophiles would give compounds in the perfragilin
series. Reaction of 5 and 9 in refluxing ether gave a low
yield of a spiro product 22 in 26% yield (Scheme 5). The 1H
NMR spectrum of 22 showed two doublets at d 7.16 and
6.31 confirming that the unsubstituted carbon–carbon
double bond of the quinone 5 had not formed a Diels–
Alder adduct with the diene. Also there was a doublet at d
6.23 which was coupled to a broad signal d 6.46 which was
considered to be due to an amide proton. Two geminal
The serendipitous synthesis of 14–17 indicated that
perfragilin A (1) and other substituted amino analogues
could be synthesized from perfragilin B (2) by selective
displacement of the C-7 thiomethoxy group with ammonia
or other amines. Indeed, reaction of 2 with aqueous
ammonia in acetonitrile yielded 1 in 22% yield along with
Scheme 5.

1352
V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
Scheme 6.
proton signals at d 2.56 and 3.09 and the t-BuMe2Si group
resonances were also present. Furthermore, one of the 13C
NMR carbonyl carbon resonances of the starting quinone
was lacking, but there were signals for an amide carbonyl (d
165.7) and an ortho-amide carbon C-2 (d 95.3). This led to
the conclusion that one of the carbonyl carbons of 5 had
reacted with the diene 9 to yield the spiro compound 22. A
similar spiro compound has already been reported in
connection with the synthesis of amphimedine using the
azadiene 9.10
between H-5 and H-11 and lack of NOE between H-2/H-11.
Compound 23 hydrolyzed to 26 upon storage in chloroform
for a few days. Reduction of 23 with Zn/AcOH afforded the
phenol derivative 27. Ultrasonication-promoted21 reaction
of 20 and 9 in ether yielded spiro adduct 23 in 28% yield,
but none of the desired Diels–Alder product. A t-butyl-
dimethylsilyl triflate catalyzed reaction22 of 20 and 9 in
ether gave 23 in 3% yield and 75% of the starting material
was recovered.
When 2,5-dichloroquinone 20 was reacted with the diene
9 in chloroform at refluxing temperature, 5% of the
adduct 23 was obtained and 77% unreacted quinone was
recovered.
The 13C NMR spectrum and the mass data of m/z 378 were
in good agreement with structure 22. The stereochemistry at
C-6 was established from observing an NOE between one of
the H-5 protons (d 2.56) and H-11. No NOE was observed
between H-2 and H-11 as would be expected from the
diastereoisomer with the opposite configuration at C-6, see
Scheme 5.
Dienophile 2,5-dimethylthioquinone 21 did not react with 9
under normal refluxing conditions. However, when 21 and 9
were reacted in 5 M LiClO4/ether23,24 at room temperature,
the diastreoisomers 24a and 24b were obtained in a 1:4
ratio. The 1H NMR spectra of 24a and 24b showed similar
resonances except that the signals for the C-5 diastereoiso-
meric protons were about 0.5 ppm apart in the spectrum of
24a whereas they were 1.0 ppm apart in 24b. The structures
of these diastereoisomers were deduced from 1H, 13C NMR
spectra and NOE analysis following arguments similar to
those invoked for 22. The molecular formula, C17H28NO4-
S2Si, was confirmed for 24b from high resolution FAB MS
analysis. For the minor diastereoisomer, 24a, the olefinic
proton resonance at C-11 showed NOE with one of the
protons at C-5 (d 2.96) and the methylthio group at d 2.20,
while the methylthio group at d 2.36 showed NOE with the
H-2 proton and the olefinic proton at H-8. This is only
consistent with the isomer 24a. The signal for the olefinic
proton at C-11 in 24b showed an NOE with H-2 and one of
the proton signals at C-5 (d 3.28), while both C-5 protons
showed an NOE with one of the methylthio groups (d 2.36).
This is only consistent with structure 24b in the confor-
mation shown.
Adduct 22 hydrolyzed to 25 during storage in an NMR tube
(CDCl3) for a few days at 48C, presumably due to the
1
presence of a trace of water (Scheme 6). The H NMR
spectrum of 25 showed an additional signal for a hydroxyl
proton at d 3.75 and signals for the formamide group at d 8.6
and 9.5, but lacked the proton resonance at d 6.23 due to H-2
of 22. The 13C NMR spectrum of 25 showed three carbonyl
resonances (d 160.9, 168.9, 175.9) and lacked the ortho-
amide carbon resonance present in 22. Mass spectral data
[263, Mþ, 265 (Mþ2)þ] was also in good agreement with
the structure 25. It is not known whether 22 (and 23, 24, see
below) is formed by a concerted or two-step process.
Calculations currently in progress indicate that it is a two-
step process with initial addition of the quinone oxygen to
the imino moiety of 9.20
Two other quinones were subjected to the Diels–Alder
reaction with the azadiene 9 to see if they also reacted
preferentially with the carbonyl group. Reaction of 2,5-di-
chlorobenzoquinone (20) with 9 in diethyl ether at room
temperature produced the spiro compound 23 in 44% yield
and none of the “normal” Diels–Alder product (Scheme 5).
The structure of 23 was deduced from NMR data following
arguments parallel to those applied for 22. High resolution
mass data confirmed the formula. The stereochemistry was
again assigned on the basis of an NOE effect observed
In order to promote the desired reaction between 5 and 9
Lewis acid catalysis was tried. When ethylaluminum
dichloride was used to catalyze the reaction in CH2Cl2 at
2788C (Scheme 7), the O-ethylated hydroquinol 28 was
obtained in 75–85% yield. This reaction and related ones
are reported elsewhere.25–27

V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
1353
Scheme 7.
3. Biological evaluation
experiments were performed on Varian XL-300, VXR-400
and VXR-500 instruments; signals are reported in parts per
million (d), referenced to the solvent used. All NMR pulse
sequences were run using standard Varian software version
4.3. IR spectra were recorded on a Bio-Rad 3240-spc FT
spectrophotometer. Freshly purified samples were used for
measurement of physical constants and spectral data. The
reaction mixtures were separated using preparative TLC
plates coated with silica gel using a Chromatotron model
7924 (Harrison Research Co.). Freshly purified samples
were used for measurement of physical constants and
spectral data.
Natural perfragilin B was found to be cytotoxic to P-388
murine leukemia cells (ED50 0.07 mg/mL). Synthetic
perfragilin B was tested against the NCI 60-cell line
tumor panel8 where the average molar log10 GI50 for five
leukemia cell lines was 26.24, and the mean-graph
midpoint log GI50 against all cell lines was 25.34. Some
selectivity against renal and breast cell lines was observed in
the overall panel evaluation. Pefragilin B (2) was evaluated
further in NCI’s in vivo hollow fiber assay against 12 cell
lines but was found not to meet NCI’s criteria for further in
vivo testing. Perfragilin B was also found to be inactive in
an in vitro anti-HIV drug screen. Perfragilin B (2) and
synthetic compounds 11–13, 16, and 19 were screened in
the Corbett–Valeriote soft agar diffusion assay28 which
evaluates compounds for differential cytotoxicity between
human leukemia and various human and murine solid
tumors. None of the compounds showed solid tumor
selectivity. Compound 16 was slightly more cytotoxic to
two leukemia cell lines (murine L1210 and human CCRF-
CEM) than perfragilin B (2); zone sizes in the primary assay
were as follows: [mg/disk, L1210/CCRF-CEM] 2: 16.5,
450/200; 16: 18, 650/500. The activity of 16 is interesting
from a structure–activity relationship point of view in that
perfragilin A (1), which has a similar substitution pattern
but in which the aromatic amino group is not substituted, is
much less active in vitro than perfragilin B (2) (see opening
paragraph).
5.1.1. 4,5-Dichlorotricyclo[6.2.1.02,7]undeca-4,9-diene-
3,6-dione (6). 2,3-Dichloro-1,4-benzoquinone (5) was
prepared from 1,4-benzoquinone according to the procedure
of Norris13 except that the intermediate 5,6-dichlorocyclo-
hexen-2-ene-1,4-dione was prepared by the following
procedure.14 To a stirred solution of benzoquinone
(600 mg, 5.56 mmol) in dry ether (14 mL) was slowly
added (3 mL/h) a solution of sulfuryl dichloride (1.0 mL,
13.24 mmol) in ether (6 mL) which had previously been
treated with triethylamine (0.08 mL, 0.28 mmol, see
below).14 After the addition, the mixture was stirred for an
additional 30 min and the solvent was evaporated on a
rotary evaporator first using aspirator pressure and then
a high vacuum to produce a slightly yellow solid in
quantitative yield. This product was used directly for
preparing 6.
To a solution of 2,3-dichloro-1,4-benzoquinone (5,
1.0 mmol) dissolved in ether (5 mL) was added at room
temperature 0.2 mL of freshly distilled cyclopentadiene.
The solution was stirred for 5 h and then solvent removed
under reduced pressure first using a water aspirator, then
under high vacuum for 2 h. The product 6 was analyzed by
1H NMR and this indicated the presence only the endo
adduct in quantitative yield. Light yellow solid mp 104–
1068C (lit.15 109–1108C); 1H NMR (CDCl3) d 1.49 (d, 1H,
J¼8.8 Hz, H-11), 1.59 (d, 1H, J¼8.8 Hz, H-11), 3.42 (dd,
2H, J¼1.8 Hz, H-2, H-7), 3.61 (m, 2H, H-1, H-8), 6.10 (t,
2H, J¼1.8 Hz, H-9, H-10); 13C NMR (CDCl3) d 48.6 (C-2,
C-7), 48.9 (C-1, C-8), 49.5 (C-11), 135.4 (C-9, C-10), 147.3
(C-4, C-5), 188.8 (C-3, C-6) ppm; LREIMS obs m/z 241.9
(100%), 243.9 (60.6%).
4. Conclusions
In summary, an improved synthesis of perfragilin B (45%
overall from 5) was developed along with the synthesis of
two N-alkylated analogues 11 and 12. Perfragilin A (1) and
various of its amino alkylated analogues were prepared by
regioselective displacement of one thiomethoxy group in
perfragilin B (2). Perfragilin B was found to be inactive in
vivo anticancer testing (hollow fiber assay) although it is
quite cytotoxic. The synthetic analogues of perfragilin A
and B were in general less cytotoxic than 2, except for 16
which was slightly more cytotoxic.
5. Experimental
5.1. General
5.1.2. 4,5-Dithiomethoxytricyclo[6.2.1.02,7]undeca-4,9-
diene-3,6-dione (7). A solution of 4,5-dichlorotricyclo-
[6.2.1.02,7]undeca-4,9-diene-3,6-dione (6, 341 mg, 1.40 mmol)
in 20 mL of dichloromethane was placed into a separatory
funnel. To this mixture was added at once a solution of
sodium thiomethoxide (197 mg, 2.81 mmol) and tetrabutyl-
ammonium hydrogen sulfate (20 mg, 0.06 mmol) in 20 mL
of water. The mixture was shaken for 2 min and the phases
High resolution fast atom bombardment mass spectra
(HRFABMS) were recorded in a 3-NBA matrix in the
positive ion mode on a VG ZAB-E mass spectrometer. Low
resolution electron-impact mass spectra (12 eV) were
measured on a Hewlett Packard 5985 instrument. NMR

1354
V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
separated. The organic phase was washed with water
(8 mL), dried over anhydrous sodium sulfate, and the
solvent evaporated under reduced pressure producing 7 as a
yellow solid (361 mg, 97%). Mp(crude) 110–1128C
chromatographed over a silica gel column and eluted with
CH2Cl2/MeOH (95:5).
5.2.1. Perfragilin B (2)9 [2,3,5,8-tetrahydro-6,7-di-(thio-
methoxy)-2-methyl-3,5,8-trioxoisoquinoline]. Obtained in
75% yield (13.9 mg from 17 mg of 10) using methyl iodide
as the alkylating agent, mp 120–1218C; IR (film) nmax 1679
(m), 1635 (m) cm21; 1H NMR (CDCl3) d 2.68 (s, 3H, SMe),
2.74 (s, 3H, SMe), 3.65 (s, 3H, N–Me), 7.08 (s, 1H, H-4),
8.24 (s, 1H, H-1); 13C NMR (CDCl3) d 18.1 (SMe), 18.7
(SMe), 38.5 (N–Me), 111.9 (C-9), 117.4 (C-4), 139.7
(C-10), 142.4 (C-1), 147.3 (C-6), 150.7 (C-7), 162.5 (C-3),
175.6 (C-8), 176.6 (C-5).
1
(lit.15113–1158C); H NMR (CDCl3) d 1.47 (d, 1H, J¼
8.8 Hz, H-11), 1.61 (d, 1H, J¼8.8 Hz, H-11), 2.46 (s, 3H,
Me), 3.33 (dd, 2H, J¼1.8 Hz, H-2, H-7), 3.45 (m, 2H, H-1,
H-8), 6.08 (t, 2H, J¼1.8 Hz, H-9, H-10) ppm; 13C NMR
(CDCl3) d 16.8 (Me), 46.8 (C-2, C-7), 48.2 (C-1, C-8), 50.5
(C-11), 136.1 (C-9, C-10), 150.2 (C-4, C-5), 191.4 (C-3,
C-6) ppm.
5.1.3. 2,3-Di-(thiomethoxy)-1,4-benzoquinone (8). Com-
pound 7 (60 mg, 0.22 mmol) was ground to a fine powder
and placed in the terminal round bottom flask (10 mL) of
a triple bulb (10 mL ea.) Kugelrohr short-path distillation
tube. This glassware assembly was connected to a vacuum
pump (0.5 mmHg) and placed into a Kugelrohr oven
preheated to 165–1708C with one bulb remaining outside
for cooling with dry ice. After 3–4 min a red material
distilled to the edge of the first bulb. The distillation bulbs
were removed from the oven and left to cool under vacuum.
The reaction product (49 mg crude yield) was removed from
the first bulb by dissolving it in dichloromethane. 1H NMR
analysis indicated that the mixture was composed of 8 and
the corresponding hydroquinone of 715 in a ratio of 9:1; 1H
NMR (CDCl3) d 2.63 (s, 6H, SMe), 6.72 (s, 2H, Holefin).
5.2.2. N-Demethyl-N-n-butyl perfragilin B (11) [2,3,5,8-
tetrahydro-6,7-di-(thiomethoxy)-2-n-butyl-3,5,8-trioxo-
isoquinoline]. Obtained in 83% yield (10.6 mg from 10 mg
of 10) using n-butyl iodide as the alkylating agent. IR (film)
n
max 1694 (m), 1654 (m), 1636 (m) cm21; 1H NMR (CDCl3)
d 0.95 (t, 3H, J¼7 Hz, Me), 1.37 (t, 2H, J¼7 Hz, CH2), 1.75
(p, 2H, J¼7 Hz, CH2), 2.67 (s, 3H, SMe), 2.74 (s, 3H, SMe),
4.01 (t, 2H, J¼7 Hz, CH2–N), 7.06 (s, 1H, H-4), 8.24 (s, 1H,
H-1); 13C NMR (CDCl3) d 13.5 (Me), 18.0 (SMe), 18.6
(SMe), 19.7 (CH2), 31.1 (CH2), 50.5 (N–CH2), 111.7 (C-9),
117.7 (C-4), 139.2 (C-10), 141.6 (C-1), 147.2 (C-6), 150.6
(C-7), 162.0 (C-3), 175.3 (C-5), 176.6 (C-8); LREIMS
(12 eV) m/z (relative intensity) 325 (Mþ, 41), 308 (100);
HRFABMS obs. m/z 326,0884 ([Mþ3]þ (calcd for
C15H20NO3S2, 326.0884).29
5.1.4. N-Demethyl-perfragilin B (10)9 [2,3,5,8-tetrahydro-
6,7-di-(thiomethoxy)-3,5,8-trioxoisoquinoline]. A solu-
tion of 8 (15 mg, 0.075 mmol) and azadiene 9 (90 mg,
0.225 mmol) in dry benzene (1.5 mL) was refluxed for 3 h
under nitrogen. To this hot mixture was added 5 drops of
concentrated hydrochloric acid and heating continued for 15
more minutes. After cooling, the solvent was evaporated
under reduced pressure (water aspirator) then under high
vacuum for 3 h. The residue was chromatographed on a
silica gel column and eluted initially with CH2Cl2 (150 mL)
then with CH2Cl2/MeOH (95:5). The desired product 10
(12.6 mg, 63%) is orange and moved on the column only
when the latter solvent mixture was introduced. Orange
solid; mp 208–2098C; IR (film) 1683 (s), 1652 (s), 1630
5.2.3. N-Demethyl-N-benzyl perfragilin B (12) [2,3,5,8-
tetrahydro-6,7-di-(thiomethoxy)-2-benzyl-3,5,8-trioxo-
isoquinoline]. Obtained in 79% yield (6.3 mg from 6 mg of
10) yield using benzyl chloride as the alkylating agent. IR
1
(film) nmax 1694 (m), 1654 (m), 1636 (m) cm21; H NMR
(CDCl3) d 2.65 (s, 3H, SMe), 2.71 (s, 3H, SMe), 5.19 (s, 2H,
N–CH2), 7.12 (s, 1H, H-4), 8.23 (s, 1H, H-1); 13C NMR
(CDCl3) d 18.1 (SMe), 18.7 (SMe), 53.0 (N–CH2), 112.2
(C-9), 118.0 (C-4), 128.5 (Ph), 128.8 (Ph), 129.2 (Ph), 134.7
(Ph), 139.4 (C-10), 141.5 (C-1), 147.2 (C-6), 150.8 (C-7),
162.1 (C-3), 175.2 (C-5), 176.5 (C-8); HRFABMS obs. m/z
360.0665 ([Mþ3]þ (calcd for C18H18NO3S2, 360.0728).29
1
(s) cm21; H NMR (CDCl3) d 2.69 (s, 3H, SMe), 2.76 (s,
3H, SMe), 5.92 (s, 1H, N–H), 7.12 (s, 1H, H-4), 8.21 (s, 1H,
H-1); 13C NMR (CDCl3) d 18.1 (SMe), 18.7 (SMe), 113.3
(C-9), 117.9 (C-4), 138.7 (C-1), 141.2 (C-10), 146.9 (C-6),
151.2 (C-9), 157.2 (C-3), 175.1 (C-8), 176.3 (C-5);
LREIMS 12 eV) m/z (relative intensity) 267 (Mþ, 27),
252 (100); HRFABMS obs. m/z 268.0102 ([Mþ1]þ (calcd
for C11H9NO3S2, 268.0102).
5.3. Reaction of 10 with methyl iodide in DMF
To a solution of 10 (17 mg, 0.064 mmol) in 1.5 mL of DMF
was added methyl iodide (12 equiv., 0.05 mL), anhydrous
potassium carbonate (18 mmol) and TDA-1 (2 drops). The
mixture was stirred at 708C under nitrogen for 2 h, poured
into 15 mL of water and then extracted with ethyl acetate
(5£10 mL). The combined organic phase was washed with
brine (3£15 mL), dried over anhydrous sodium sulfate and
concentrated under reduced pressure. The residue was
chromatographed over silica gel and eluted with CH2Cl2/
MeOH (95:5). Perfragilin B (2) was obtained in 51% yield
along with 13–15.
5.2. General procedure for obtaining 2, 12 and 13 in
DMSO
To a solution of 10 (0.1 mmol) in 1 mL of DMSO was
added the appropriate alkylating agent (20–40 equiv.),
anhydrous potassium carbonate (0.3 mmol) and 1–2
drops of TDA-1.17 The mixture was stirred at room
temperature under nitrogen for 3 h, poured into (15 mL)
water and then extracted with dichloromethane (5£15 mL).
The combined organic phase was washed with brine
(3£15 mL), dried over anhydrous sodium sulfate, and
concentrated under reduced pressure. The residue was
5.3.1. 2,3,5,8-Tetrahydro-4,6,7-tri-(thiomethoxy)-2-
methyl-3,5,8-trioxoisoquinoline (13). Obtained in 7%
(1.5 mg) yield. IR (film) nmax 1684 (s), 1652 (s), 1630 (s),
1
1558 (s) (s) cm21; H NMR (CDCl3) d 2.65 (s, 3H, Me),
2.66 (s, 3H, Me), 2.68 (s, 3H, Me), 3.63 (s, 3H, N–Me), 8.10
(s, 1H, H-1); 13C NMR (CDCl3) d 18.0 (SMe), 18.1 (SMe),

V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
1355
18.2 (SMe), 39.0 (N–Me), 112.6 (C-9), 135.4 (C-10), 138.2
(C-1), 145.7 (C-4), 146.6 (C-6), 150.9 (C-7), 160.8 (C-3),
175.3 (C-8), 177.4 (C-5); LRFABMS m/z (relative intensity)
328 [(Mþ1)þ, 15]; HRFABMS obs. m/z 328.0145 ([Mþ1]þ
(calcd for C13H14NO3S3, 328.0136).
J¼7 Hz, 2H, CH2), 2.29 (s, 3H, SMe), 3.47 (d, J¼6 Hz, 6H,
NHMe), 3.99 (t, J¼7 Hz, CH2–N), 6.76 (bs, 1H, NH), 7.13
(s, 1H, H-4), 8.22 (s, 1H, H-1); 13C NMR (CDCl3) d 13.6
(Me), (SMe, not obs.), 19.8 (CH2), 31.2 (CH2), 33.7
(NHMe), 50.5 (N–CH2), (C-9, not obs.), 117.0 (C-4),
(C-7, not obs.), 139.9 (C-10), 142.0 (C-1), 153.0 (very weak,
C-7), 162.6 (C-3), 177.0 (very weak, C-5), 180.1 (very
weak, C-8); LRFABMS m/z (relative intensity) 307
[(Mþ1)þ, 100); HRFABMS obs. m/z 307.1111 ([Mþ1]þ
(Calcd for C15H19N2O3S2, 307.1116).
5.3.2. 2,3,5,8-Tetrahydro-7-dimethylamino-6-thiometh-
oxy-2-methyl-3,5,8-trioxoisoquinoline (14). Obtained in
15% (2.5 mg) yield. IR (film) nmax 3233 (bm), 1684 (s),
1
1645 (s), 1559 (m) cm21; H NMR (CDCl3) d 2.24 (s, 3H,
SMe), 3.26 (s, 6H, NMe2), 3.63 (s, 3H, NMe), 7.07 (s, 1H,
H-4), 8.17 (s, 1H, H-1); 13C NMR (CDCl3) d 18.1 (weak,
SMe), 38.4 (N–Me), 44.8 (NMe2), 111.8 (C-9), 116.0 (C-4),
116.6 (C-6, very weak), 139.7 (C-10), 142.2 (C-1), (C-7, not
obs.), 163.0 (C-3), (C-8, not obs.), 179.6 (C-5); LREI
(12 eV) m/z 279.9 [Mþ] (88%), 263.0 [M215]þ (100%).
5.4.3. 5,8-Dihydro-6,7-di-(thiomethoxy)-3-butoxy-5,8-
dioxoisoquinoline (18). Obtained in 5% yield. IR (film)
n
3H, J¼7 Hz, Me), 1.46 (h, 2H, J¼7 Hz, CH2), 1.76 (p, 2H,
J¼7 Hz, CH2), 2.67 (s, 3H, SMe),), 2.78 (s, 3H, SMe), 4.41
(t, 2H, J¼7 Hz, CH2–N), 7.20 (s, 1H, H-4), 8.85 (s, 1H,
H-1); LREIMS m/z (relative intensity) 323 (Mþ, 64), 308
(100), 251 (17); HRFABMS obs. m/z 326.0897 (Mþ3)þ
(Calcd for C15H19NO3S2 326.0885).29
max 1735 (bm), 1664 (s) cm21; 1H NMR (CDCl3) d 0.96 (t,
5.3.3. 2,3,5,8-Tetrahydro-7-methylamino-6-thiometh-
oxy-2-methyl-3,5,8-trioxoisoquinoline (15). Obtained in
17% (3 mg) yield. IR (film) nmax 1684 (m), 1652 (s), 1600
1
(m) cm21; H NMR (CDCl3) d 2.31 (s, 3H, SMe), 3.48 (d,
3H, J¼6 Hz, NHMe), 3.64 (s, 3H, NMe), 6.90 (bs, 1H, NH),
7.16 (s, 1H, H-4), 8.27 (s, 1H, H-1); 13C NMR (CDCl3) d
18.5 (very weak, SMe), 33.7 (NH–Me), 38.4 (NMe), 116.6
(C-4), (C-9, not obs.), 131.3 (C-6), 140.2 (C-10), 142.5
(C-1), (C-7, not obs.), 163.0 (C-3), 176.9 (C-5), (C-8, not
obs.); LRFABMS m/z (relative intensity) 264 (Mþ, 100),
249 (56), 231 (29); HRFABMS obs. m/z 265.0643 ([Mþ1]þ
(calcd for C12H13N2O3S, 265.0647).
5.4.4. Perfragilin A (1) [2,3,5,8-tetrahydro-7-amino-6-
thiomethoxy-2-methyl-3,5,8-trioxoisoquinoline]. To
a
solution of perfragilin B (2) (8 mg, 0.03 mmol) in
acetonitrile (1.5 mL) was added a solution of concentrated
NH4OH (0.1 mL) and the mixture stirred at room tempera-
ture for 1 h. The reaction mixtures was initially concen-
trated in a rotary evaporator and then the residue dried under
high vacuum overnight. Chromatography on a silica
gel preparative TLC plate (500 mm) using CH2Cl2/MeOH
(95:5) as eluent afforded 1a as a yellow solid, 22% (1.7 mg)
5.4. Reaction of 10 with n-butyl chloride in DMF
1
yield. H NMR (CDCl3) d 2.68 (s, 3H, SMe), 3.64 (s, 3H,
To a solution of 10 (13 mg, 0.05 mmol) in 1.5 mL of DMF
was added n-butyl chloride (0.05 mL), anhydrous potassium
carbonate (15 mg, 0.15 mmol) and TDA-1 (2 drops). The
mixture was stirred at 708C under nitrogen for 5 h, poured
into 20 mL of water and then extracted with ethyl acetate
(4£15 mL). The combined organic phase was washed with
brine, dried over anhydrous sodium sulfate and concentrated
under reduced pressure. The residue was chromatographed
on a silica gel TLC preparative plate (500 mm) and eluted
with CH2Cl2/MeOH (95:5).
N–Me), 7.17 (s, 1H, H-4), 8.29 (s, 1H, H-1); 13C NMR
(CDCl3) d 16.7 (SMe), 38.4 (N–Me), 110.5 (C-6), 113.1
(C-9), 117.2 (C-4), 140.2 (C-10), 142.5 (C-1), 152.1 (C-7),
162.9 (C-3), 175.2 (C-8), 176.9 (C-5); LRFABMS m/z 251
(16%); HRFABMS obs. m/z 251.0496 [Mþ3]þ (calcd for
C11H10N2O3S, 251.0490).29
5.4.5. N-Benzyl perfragilin A (19) [2,3,5,8-tetrahydro-
7-benzylamino-6-thiomethoxy-2-methyl-3,5,8-trioxoiso-
quinoline]. To a solution of perfragilin B (2) (15 mg,
0.05 mmol) in CH2Cl2 (5 mL) was added benzylamine
(0.05 mL) and the mixture stirred at room temperature for
2 h. The deep red reaction mixture was initially
concentrated in a rotary evaporator, then worked up in
the same manner as for 1 to give 19 as a yellow glass in
29% (5 mg) yield. IR (film) nmax 3309 (bm), 1684 (s),
5.4.1. 2,3,5,8-Tetrahydro-7-dimethylamino-6-thiometh-
oxy-2-n-butyl-3,5,8-trioxoisoquinoline (16). Obtained in
33% yield (5.2 mg) yield. IR (film) nmax1684 (m), 1654 (m),
1
1559 (m) cm21; H NMR (CDCl3) d 0.93 (t, 3H, J¼7 Hz,
Me), 1.38 (sextet, 2H, J¼7 Hz, CH2), 1.71 (quint., 2H, J¼
7 Hz, CH2), 2.21 (s, 3H, SMe), 3.24 (s, 6H, NMe2), 3.98 (t,
2H, J¼7 Hz, CH2–N), 7.04 (s, 1H, H-4), 8.12 (s, 1H, H-1);
13C NMR (CDCl3) d 13.5 (Me), 18.1 (SMe), 19.8 (CH2),
31.1 (CH2), 44.7 (NMe2), 50.4 (N–CH2), 111.7 (C-9), 116.3
(C-4), 123.6 (C-6), 139.3 (C-10), 141.5 (C-1), 155.5 (C-7),
162.5 (C-3), 178.7 (C-8), 179.2 (C-5); LRFABMS m/z (rela-
tive intensity) 321 [(Mþ1)þ, 100), 307 (82); HRFABMS
obs. m/z 321.1286 ([Mþ1]þ (calcd for C16H21N2O3S2,
321.1273).
1
1652 (s), 1558 (s) cm21; H NMR (CDCl3) d 2.22 (s, 3H,
SMe), 3.65 (s, 3H, NMe), 6.95 (bs, 1H, N–H), 7.15 (s,
1H, H-4), 8.27 (s, 1H, H-1); 13C NMR (CDCl3) d 18.2
(very weak, SMe), 38.4 (NCH3), 49.8 (CH2), (C-9, not
obs.), 116.7 (C-4), 125.6 (C-6), 127.5 (C-H, o or m-Ph),
127.9 (C-H, p-Ph), 129.0 (C-H, o or m-Ph), 137.8 (C, Ph),
140.1 (C-10), 142.9 (C-1), 157.2 (C-7, very weak), 162.9
(C-3), 176.8 (C-5), (C-8, not obs.); LREIMS m/z (relative
intensity) 340 (Mþ, 100); HRFABMS obs. m/z 341.0947
[Mþ1]þ (calcd for C18H17N2O3S, 341.0960).
5.4.2. 2,3,5,8-Tetrahydro-7-methylamino-6-thiometh-
oxy-2-n-butyl-3,5,8-trioxoisoquinoline (17). Obtained in
11% yield (1.2 mg) yield. IR (film) nmax 3230 (bm), 1684
(s), 1652 (s), 1558 (s) cm21; 1H NMR (CDCl3) d 0.94 (t, J¼
7 Hz, 3H, Me), 1.36 (sextet, J¼7 Hz, 2H, CH2), 1.73 (quint.,
5.4.6. 1-Oxa-3-aza-2-(t-butyldimethylsilyloxy)-7,8-di-
chloro-4,9-dioxospiro[5,5]undeca-7,10-diene (22). A solu-
tion of 5 (24 mg, 0.14 mmol) and 9 (71 mg, 0.19 mmol)
in anhydrous diethyl ether (1 mL) was refluxed under a

1356
V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
nitrogen atmosphere for 3.5 h. After cooling to rt the
reaction was quenched by addition of methanol and the
solvent was removed under reduced pressure. The residue
was chromatographed on a silica gel flash column using
dichloromethane/acetone (95:5) to give 22 as yellow solid
(13.5 mg, 26% yield); mp 109–1108C; IR (film) nmax 3290
(br), 1685 cm21; 1H NMR (CDCl3) d 0.13 (s, 3H, Si–Me),
0.16 (s, 3H, Si–Me), 0.89 (s, 9H, Si–t-Bu), 2.56 (d, 1H,
J¼16 Hz, H-50), 3.09 (d, 1H, J¼16 Hz, H-5), 6.23 (d, 1H,
J¼2 Hz, H-2), 6.31 (d, 1H, J¼10 Hz, H-10), 6.46 (br, 1H,
NH), 7.16 (d, 1H, J¼10 Hz, H-11); 13C NMR (CDCl3) d
25.2 (Si–Me), 24.5 (Si–Me), 17.7 (Si–t-Bu), 25.4 (Si–t-
Bu), 39.1 (C-5), 73.7 (C-6), 95.3 (C-2), 125.3 (C-10), 133.2
(C-8), 147.5 (C-11), 149.8 (C-7), 165.7 (C-4), 175.9 (C-9);
LRFABMS m/z 378 (relative intensity) [(MþH)þ, 64), 380
[(MþHþ2)þ, 42].
(s, 3H, Si–Me), 0.90 (s, 9H, Si–t-Bu), 2.19 (s, S–Me at
C-10), 2.36 (s, 3H, S–Me at C-7), 2.36 (d, 1H, J¼16 Hz,
H-50), 3.28 (d, 1H, J¼16 Hz, H-5), 6.04 (s, 1H, H-8), 6.12
(d, 1H, J¼2 Hz, H-2), 6.31 (s, 1H, H-11), 6.45 (br, 1H, NH);
13C NMR (CDCl3) d 25.2 (Si–Me), 24.5 (Si–Me), 13.4
(S–Me at C-10), 14.5 (S–Me at C-7), 17.9 (Si–t-Bu), 25.5
(Si–t-Bu), 43.7 (C-5), 75.1 (C-6), 94.3 (C-2), 118.8 (C-8),
131.3 (C-11), 140.3 (C-10), 166.7 (C-7), 167.3 (C-4), 177.9
(C-9); HRFABMS m/z 402.1265 [Mþ1]þ (calcd for
C17H28NO4SiS2, 402.1229).
5.5. General procedure for obtaining 26 and 27
When the compounds 22 (2 mg) and 23 were stored in
CDCl3 at 48C for several days they hydrolyzed to 26 and 27,
respectively, in quantitative yields.
5.4.7. 1-Oxa-3-aza-2-(t-butyldimethylsilyloxy)-7,10-
dichloro-4,9-dioxospiro[5,5]undeca-7,10-diene (23). A
solution of 20 (50 mg, 0.28 mmol) and 9 (135 mg,
0.34 mmol) in anhydrous diethyl ether (1 mL) was refluxed
under a nitrogen atmosphere for 3 h. After cooling to rt the
reaction was quenched by addition of methanol and the
solvent was removed under reduced pressure. The residue
was chromatographed on a silica gel flash column using
dichloromethane/acetone (95:5) to give 23 as yellow solid
(48 mg, 44% yield); mp 119–1208C; IR (film) nmax 3240
(br), 1682 cm21; 1H NMR (CDCl3) d 0.11 (s, 3H, Si–Me),
0.14 (s, 3H, Si–Me), 0.88 (s, 9H, Si–t-Bu), 2.59 (d, 1H,
J¼16 Hz, H-50), 3.04 (d, 1H, J¼16 Hz, H-5), 6.18 (d, 1H,
J¼2 Hz, H-2), 6.52 (d, 1H, J¼10 Hz, H-8), 7.06 (br, 1H,
NH), 7.39 (d, 1H, J¼10 Hz, H-11); 13C NMR (CDCl3) d
25.2 (Si–Me), 24.5 (Si–Me), 17.7 (Si–t-Bu), 25.4 (Si–t-
Bu), 38.5 (C-5), 73.5 (C-6), 95.2 (C-2), 127.8 (C-8), 131.5
(C-10), 143.1 (C-11), 154.5 (C-7), 165.7 (C-4), 176.0 (C-9);
HRFABMS obs. m/z 378.0667 [Mþ1, 49]þ (calcd for
C15H22NO4SiCl2, 378.0695), 380.0609 [(MþHþ2)þ, 38].
5.5.1. 2,3-Dichloro-4-N-formylacetamido-4-hydroxy-
cyclohexadienone (25). Yellow solid; mp 112–1138C; IR
(film) nmax 3305 (br), 1743, 1683, cm21; 1H NMR (CDCl3)
d 2.65 (d, 1H, J¼16 Hz, H-70), 3.24 (d, 1H, J¼16 Hz, H-7),
6.39 (d, 1H, J¼10 Hz, H-6), 7.09 (d, 1H, J¼10 Hz, H-5),
8.60 (br, 1H, NH), 9.05 (d, 1H, J¼10 Hz, H-10); 13C NMR
(CDCl3) d 45.5 (C-7), 71.7 (C-4), 127.0 (C-6), 133.3 (C-2),
146.5 (C-5), 150.6 (C-3), 160.9 (C-10), 168.9 (C-8), 175.9
(C-1); LREIMS m/z 263 (Mþ, 64), 265 (Mþ2)þ.
5.5.2. 2,5-Dichloro-4-N-formylacetamido-4-hydroxy-
cyclohexadienone (26). Yellow solid. IR (film) nmax
3400–3250, 1743, 1682 cm20 1; 1H NMR (CDCl3þCD3OD)
d 2.70 (d, 1H, J¼15 Hz, H-7 ), 2.90 (d, 1H, J¼15 Hz, H-7),
6.38 (s, 1H, H-6), 7.12 (s, 1H, H-5), 8.90 (s, 1H, H-10);
LREIMS m/z 263 (Mþ, 64), 265 (Mþ2)þ.
5.5.3. 20,50-Dichloro-4-hydroxyphenylacetamide (27). A
solution of 23 (24 mg, 0.063 mmol) in ether was refluxed
with zinc dust (15 mg) and acetic acid (0.5 mL) overnight.
The resulting mixture was partitioned between chloroform
and water. The combined chloroform layers afforded 27 as
white solid in a quantitative yield after removal of solvent;
mp 109–1108C; IR (film) nmax 3350, 1668 cm21; 1H NMR
(CDCl3þCD3OD) d 3.67 (s, 2H, H-2), 6.95 (s, 1H, H-30),
5.4.8. 1-Oxa-3-aza-2-(t-butyldimethylsilyloxy)-7,10-di-
(methylthio)-4,9-dioxospiro[5,5]undeca-7,10-diene (24a
and 24b). A solution of 21 (60 mg, 0.30 mmol) and 9
(225 mg, 0.56 mmol) in 0.5 M LiClO4/ether was stirred at rt
for 48 h. The reaction was quenched by addition of 45 mL
of cold water and extracted with chloroform (3£45 mL).
The combined chloroform extracts were evaporated under
reduced pressure and the residue chromatographed on a
silica a gel flash column using a gradient from dichloro-
methane to acetone. After repetitive chromatography 24a
and 24b were obtained as yellow solids in 4% and 16%
(20.9 mg) yield, respectively; 24a; mp 173–1748C; IR
7.20 (s, 1H, H-60), 9.06 (br s, OH); 13C NMR (CDCl3þ
-
CD3OD) d 39.7 (C-2), 117.3 (C-30 or 60), 119.6 (C-30 or 60),
123.0 (C-10), 132.4 (C-20 or 50), 133.4 (C-20 or 50), 153.2
(C-40), 163.4 (C-1); Low Resolution Thermospray MS m/z
220 (MþH)þ, 222 (MþHþ2) þ, 237 (MþNH4)þ, 239
[(MþNH4þ2)þ.
1
(film) nmax 3235 (br), 1651, 1567, 1032 cm21; H NMR
Acknowledgements
(CDCl3) d 0.12 (s, 3H, Si–Me), 0.15 (s, 3H, Si–Me), 0.89
(s, 9H, Si–t-Bu), 2.20 (s, S–Me at C-10), 2.36 (s, 3H, S–Me
at C-7), 2.56 (d, 1H, J¼16 Hz, H-50), 2.96 (d, 1H, J¼16 Hz,
H-5), 6.02 (s, 1H, H-8), 6.18 (d, J¼2 Hz, 1H, H-2), 6.45 (br,
1H, NH), 6.60 (s, 1H, H-11); 13C NMR (CDCl3) d 25.1
(Si–Me), 24.3 (Si–Me), 13.2 (S–Me at C-10), 14.3 (S–Me
at C-7), 17.8 (Si–t-Bu), 25.5 (Si–t-Bu), 43.5 (C-5), 74.4
(C-6), 95.2 (C-2), 118.8 (C-8), 134.7 (C-11), 138.7 (C-10),
166.1 (C-7), 166.7 (C-4), 178.2 (C-9).
A Fellowship from CAPES (Brazil) to V. F. F. is gratefully
acknowledged. This work was supported in part by
Department of Commerce, NOAA Sea Grant Project
NA66RGO172.
References
24b: mp 171–1728C; IR (film) nmax 3217 (br), 1692, 1643,
1024 cm21; 1H NMR (CDCl3) d 0.18 (s, 3H, Si–Me), 0.19
1. Schmitz, F. J.; De Guzman, F. S.; Choi, Y.-H.; Hossain, M. B.;

V. F. Ferreira et al. / Tetrahedron 59 (2003) 1349–1357
1357
Rizvi, S. K.; van der Helm, D. Pure Appl. Chem. 1990, 62,
1393–1396.
19. Gould, S. J.; Melville, C. K. Tetrahedron Lett. 1997, 38,
1473–1476, In the case of 14 an instrument problem
contributed to the weakness of the spectrum. Compound 14
decomposed by the time a second spectral analysis was
attempted.
2. Choi, Y.-H.; Park, A.; Schmitz, F. J.; van Altena, I. J. Nat.
Prod. 1993, 56, 1431–1433.
3. Rizvi, S. K.; Hossain, M. B.; van der Helm, D. Acta
Crystallogr., Sect. C 1993, 49, 151–154.
20. Personal communication from Dr V. F. Ferreira.
21. Lee, J.; Mei, H. S.; Snyder, J. K. J. Org. Chem. 1990, 55,
5013–5016.
4. Frincke, J. M.; Faulkner, D. J. J. Am. Chem. Soc. 1982, 104,
265–269.
5. McIntyre, D. E.; Faulkner, D. J.; van Engen, D.; Clardy, J.
Tetrahedron Lett. 1979, 4163–4166.
22. Lamg-Schelkens, H.; Giomi, D.; Ghosez, L. Tetrahedron Lett.
1989, 30, 5887–5890.
6. McKee, T. C.; Ireland, C. M. J. Nat. Prod. 1987, 50, 754–756.
7. Pettit, G. R.; Collins, J. C.; Herald, D. L. D.; Boyd, M. R.;
Schmidt, J. M.; Hooper, N. A.; Tackett, L. P. Can. J. Chem.
1992, 70, 1170–1175.
23. Braun, R.; Sauer, J. Chem. Ber. 1986, 119, 1269–1274.
24. Grieco, P. A. In Organic Chemistry: Its Language and Its State
of Art; Kisaku¨rek, M. V., Ed.; VHCA/VCA: Basel/Weinheim,
1993; pp 133–146.
8. Boyd, M. R.; Paull, K. D. Drug Development Res. 1995, 34,
91–108.
25. Florjanczyk, Z.; Kuran, W.; Pasynkiewicz, S.; Kwas, G.
J. Organomet. Chem. 1976, 112, 21–28.
9. Schmitz, F. J.; Park, A. Tetrahedron Lett. 1993, 34,
3983–3984.
26. Florjanczyk, Z.; Szymanska-Zachara, E. J. Organomet. Chem.
1983, 259, 127–137.
10. Echavarren, A. M.; Stille, J. K. J. Am. Chem. Soc. 1988, 110,
4049–4053.
27. Ferreira, V. F.; Schmitz, F. J. J. Organomet. Chem. 1998, 571,
1–6.
11. McKillop, A.; Brown, S. P. Synth. Commun. 1987, 17,
657–667.
28. (a) Valeriote, F.; Corbett, T.; LoRusso, P.; Moore, R. E.;
Scheuer, P. J.; Patterson, G.; Paul, V.; Grindey, G.;
Bonjouklian, R.; Pearce, H.; Suffness, M. I. J. Pharmacog.
1995, 33, 59–66. (b) Valeriote, F.; Corbett, T.; Edelstein, M.;
Baker, L. Cancer Invest. 1996, 14, 124–141. (c) Valeriote, F.;
Grieshaber, C. K.; Media, J.; Pietraszkiewicz, H.; Hoffmann,
J.; Pan, M.; McLaughlin, S. J. Exp. Therap. Oncol. 2002, 2,
228–236.
12. Fukumi, H.; Kurihara, H.; Hata, T.; Tamura, C.; Mishima, H.;
Kubo, A.; Arai, T. Tetrahedron Lett. 1977, 3825–3828.
13. Norris, R. K.; Sternhell, S. Aust. J. Chem. 1973, 26, 333–343.
14. Ferreira, V. F.; Schmitz, F. J. Org. Prep. Proced. Int. 1998, 30,
115–116.
15. Wladislaw, B.; Marzorati, L.; Di Vita, C. Synthesis 1983,
464–466.
29. Quinones often show prominent Mþ2 ions in EIMS and Mþ3
ions in their FABMS corresponding to their reduced hydro-
quinol forms. See: Fu, X.; Hossain, M. B.; Schmitz, F. J.; van
der Helm, D. J. Org. Chem. 1997, 62, 3810–3819, and
references cited.
16. Sainte, F.; Serckx-Poncin, B.; Hesbain-Frisque, A.-M.;
Ghosez, L. J. Am. Chem. Soc. 1982, 104, 1428–1430.
17. Soula, G. J. Org. Chem. 1985, 50, 3717–3721.
18. Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory
Chemicals; Butterworth-Heinemann: Oxford, 1992; pp
192–193.