Synthesis and evaluation of a series of C3-substituted CBI analogues of CC-1065 and the duocarmycins

Article abstract of DOI:10.1021/jo010309g

The synthesis and evaluation of a series of C3-substituted 1,2,9,9a-tetrahydrocyclopropa[c]benz-[e]indol-4-one (CBI) analogues of the CC-1065 and duocarmycin alkylation subunits are detailed, including methyl and the full series of halogens. Introduction

Full text of DOI:10.1021/jo010309g

J . Org. Chem. 2001, 66, 5163-5173
5163
Syn th esis a n d Eva lu a tion of a Ser ies of C3-Su bstitu ted CBI
An a logu es of CC-1065 a n d th e Du oca r m ycin s
Dale L. Boger,* Steven R. Brunette, and Robert M. Garbaccio
Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute,
10550 North Torrey Pines Road, La J olla, California 92037
boger@scripps.edu
Received March 21, 2001
The synthesis and evaluation of a series of C3-substituted 1,2,9,9a-tetrahydrocyclopropa[c]benz-
[e]indol-4-one (CBI) analogues of the CC-1065 and duocarmycin alkylation subunits are detailed,
including methyl and the full series of halogens. Introduction of the key substituent was
accomplished through directed metalation of the seco-CBI core followed by reaction of the resultant
aryllithium with an appropriate electrophile. C3-Bromo and iodo substituents were only effectively
installed on the hindered aryllithium intermediate using a novel halogen source, 1-bromo- and
1-iodophenylacetylene, that should prove generally useful beyond the studies we describe. X-ray
crystal structures of the series show substantial distortion in the vinylogous amide due to
unfavorable steric interactions between the C3-substituent and the N2-carbamate. In the halogen
series, the N2-C2a bond length and the torsional angle ø1 smoothly increase with the increasing
size of the C3 substituent indicative of decreasing vinylogous amide conjugation through the series
(H > F > Cl > Br > I). Unlike N-Boc-CBI, this series of substituted CBI analogues proved
remarkably reactive toward solvolysis even at pH 7, where the reaction is uncatalyzed and the
reactivity order (I > Br > Cl > F > H) follows a trend consistent with the extent of vinylogous
amide conjugation and stabilization. The implications of these observations on the source of catalysis
for the DNA alkylation reaction of the natural products are discussed.
(+)-CC-10651 (1) and the duocarmycins2,3 2 and 3
(Figure 1) are the parent members of a potent class of
antitumor antibiotics. These natural products derive
their potent biological activity through a characteristic
sequence-selective alkylation of DNA that has been
shown to proceed by reversible, stereoelectronically con-
trolled adenine N3 addition to the least substituted
carbon of the activated cyclopropane.5-11 Following their
disclosure, continued extensive studies have been con-
ducted in efforts to define the factors responsible for their
(1) Hanka, L. J .; Dietz, A.; Gerpheide, S. A.; Kuentzel, S. L.; Martin,
D. G. J . Antibiot. 1978, 31, 1211.
(2) Yasuzawa, T.; Muroi, K.; Ichimura, M.; Takahashi, I.; Ogawa,
T.; Takahashi, K.; Sano, H.; Saitoh, Y. Chem. Pharm. Bull. 1995, 43,
378. Takahashi, I.; Takahashi, K.; Ichimura, M.; Morimoto, M.; Asano,
K.; Kawamoto, I.; Tomita, F.; Nakano, H. J . Antibiot. 1988, 41, 1915.
Yasuzawa, T.; Iida, T.; Muroi, K.; Ichimura, M.; Muroi, K.; Asano, K.;
Kawamoto, I.; Tomita, F.; Morimoto, M.; Nakano, H. J . Antibiot. 1988,
41, 1285.
(3) Ichimura, M.; Ogawa, T.; Takahashi, K.; Kobayashi, E.; Kawa-
moto, I.; Yasuzawa, T.; Takahashi, I.; Nakano, H. J . Antibiot. 1990,
43, 1037. Ichimura, M.; Ogawa, T.; Katsumata, S.; Takahashi, K.;
Takahashi, I.; Nakano, H. J . Antibiot. 1991, 44, 1045.
F igu r e 1.
(4) Ohba, K.; Watabe, H.; Sasaki, T.; Takeuchi, Y.; Kondo, S. J .
remarkable biological properties.11,12 Central to these
studies have been the synthesis and evaluation of struc-
tural analogues that bear either deep-seated or more
subtle substituent modifications to the alkylation subunit
(selected examples shown in Figure 2).13-22 Of the many
analogues investigated, the 1,2,9,9a-tetrahydrocyclopro-
Antibiot. 1988, 41, 1515. Ishii, S.; Nagasawa, M.; Kariya, Y.; Yama-
moto, H.; Inouye, S.; Kondo, S. J . Antibiot. 1989, 42, 1713.
(5) Boger, D. L.; J ohnson, D. S. Proc. Natl. Acad. Sci. U.S.A. 1995,
92, 3642. Boger, D. L. Acc. Chem. Res. 1995, 28, 20. Boger, D. L.
Chemtracts: Org. Chem. 1991, 4, 329.
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315. Hurley, L. H.; Needham-VanDevanter, D. R. Acc. Chem. Res. 1986,
19, 230.
(7) Boger, D. L.; Ishizaki, T.; Zarrinmayeh, H.; Kitos, P. A.; Sun-
tornwat, O. J . Org. Chem. 1990, 55, 4499. Boger, D. L.; Ishizaki, T.;
Zarrinmayeh, H.; Munk, S. A.; Kitos, P. A.; Sunthornwat, O. J . Am.
Chem. Soc. 1990, 112, 8961. Boger, D. L.; Munk, S. A.; Zarrinmayeh,
H.; Ishizaki, T.; Haught, J .; Bina, M. Tetrahedron 1991, 47, 2661.
Boger, D. L.; Ishizaki, T.; Zarrinmayeh, H. J . Am. Chem. Soc. 1991,
113, 6645. Boger, D. L.; Yun, W. J . Am. Chem. Soc. 1993, 115, 9872.
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1635.
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Boger, D. L.; J ohnson, D. S.; Yun, W.; Tarby, C. M. Bioorg. Med. Chem.
1994, 2, 115. Boger, D. L.; Zarrinmayeh, H.; Munk, S. A.; Kitos, P. A.;
Suntornwat, O. Proc. Natl. Acad. Sci. U.S.A. 1991, 88, 1431. Boger,
D. L.; Munk, S. A.; Zarrimayeh, H. J . Am. Chem. Soc. 1991, 113, 3980.
Boger, D. L.; Coleman, R. S.; Invergo, B. J .; Sakya, S. M.; Ishizaki, T.;
Munk, S. A.; Zarrinmayeh, H.; Kitos, P. A.; Thompson, S. C. J . Am.
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10.1021/jo010309g CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/28/2001

5164 J . Org. Chem., Vol. 66, No. 15, 2001
Boger et al.
F igu r e 3.
including MCBI14 (10), CCBI15 (11), F2CBI16 (12), CBQ17
(13), CNA18 (14), CBIn19 (15), MCCBI20 (16), and CPyI21
has allowed detailed investigations into the relationships
between structure, chemical reactivity, and biological
potency. To date, however, no such CBI derivatives have
addressed C3 substitution of the cyclohexadienone sys-
tem.22 Herein, we report the synthesis and evaluation of
the C3-substituted N-Boc-CBI analogues 5-9 where the
cyclohexadienone system has been directly substituted
with a series of substituents, including methyl and the
full series of halogens. Their behavior, especially a
marked uncatalyzed versus acid-catalyzed solvolysis
reactivity at pH 7 which follows reactivity trends ex-
pected of a progressively decreased vinylogous amide
conjugation, has ramifications on the potential source of
catalysis for the DNA alkylation reaction of the natural
products and their analogues.
F igu r e 2.
Syn t h esis of C3-Su b st it u t ed N-Boc-CBI An a -
logu es 5-9. The approach employed for the preparation
of 5-9 follows a general strategy for the synthesis of CBI
analogues developed in our laboratory.13 The C3-sub-
stituent was to be introduced at a late stage, such that
the synthesis could diverge from a common, advanced
intermediate. Installation of this key substituent was to
be accomplished through selective ortho-metalation of the
tricyclic seco-CBI core, utilizing a directing MOM ether
phenol protecting group (Figure 3). Reaction of the
resultant aryllithium with an appropriate electrophile
would provide the corresponding C3-substituted seco-CBI
derivative. The alternative approach of direct C3 elec-
trophilic substitution (e.g., Br2 bromination) was also
explored but found to be largely unsuccessful. Finally,
selective deprotection of the MOM ether followed by
spirocyclization would afford the desired C3-substituted
N-Boc-CBI derivatives.
MOM ether 17 was prepared in accord with a recent
preparation of CBI13 and the structurally related iso-
CBI.23 Regioselective electrophilic iodination at C4 of 1723
yielded exclusively aryl iodide 18 (NIS, TsOH, 77%),
Scheme 1. Allylation of the carbamate (NaH, allyl
bromide, Bu4NI, 99%), followed by a Bu3SnH promoted
5-exo-trig free-radical cyclization of 19 with in situ
TEMPO trap of the resultant primary radical13 provided
20 (70%). Subsequent reduction of the N-O bond was
accomplished (Zn, AcOH, 72%) without competitive re-
pa[c]benz[e]indol-4-one (CBI, 4) alkylation subunit is one
example where significant alteration of the natural
structure provided a system that retains or exceeds the
potency and biological properties characteristic of the
natural products, yet is more synthetically accessible.13
Furthermore, modification of the CBI core through the
synthesis and evaluation of second-generation analogues
(9) Sugiyama, H.; Hosoda, M.; Saito, I.; Asai, A.; Saito, H. Tetrahe-
dron Lett. 1990, 31, 7197. Sugiyama, H.; Ohmori, K.; Chan, K.-L.;
Hosoda, M.; Asai, A.; Saito, H.; Saito, I. Tetrahedron Lett. 1993, 34,
2179. Yamamoto, K.; Sugiyama, H.; Kawanishi, S. Biochemistry 1993,
32, 1059. Asai, A.; Nagamura, S.; Saito, H. J . Am. Chem. Soc. 1994,
116, 4171.
(10) Reynolds, V. L.; Molineux, I. J .; Kaplan, D. J .; Swenson, D. H.;
Hurley, L. H. Biochemistry 1985, 24, 6228. Hurley, L. H.; Lee, C.-S.;
McGovren, J . P.; Warpehoski, M. A.; Mitchell, M. A.; Kelly, R. C.;
Aristoff, P. A. Biochemistry 1988, 27, 3886. Hurley, L. H.; Warpehoski,
M. A.; Lee, C.-S.; McGovren, J . P.; Scahill, T. A.; Kelly, R. C.; Mitchell,
M. A.; Wicnienski, N. A.; Gebhard, I.; J ohnson, P. D.; Bradford, V. S.
J . Am. Chem. Soc. 1990, 112, 4633.
(11) For synthetic aspects see: Boger, D. L.; Boyce, C. W.; Garbaccio,
R. M.; Goldberg, J . A. Chem. Rev. 1997, 97, 787.
(12) For mechanistic aspects, see: Boger, D. L.; J ohnson, D. S.
Angew. Chem., Int. Ed. Engl. 1996, 35, 1439.
(13) Boger, D. L.; Ishizaki, T.; Wysocki, R. J ., J r.; Munk, S. A.; Kitos,
P. A.; Suntornwat, O. J . Am. Chem. Soc. 1989, 111, 6461. Boger, D.
L.; Ishizaki, T.; Kitos, P. A.; Suntornwat, O. J . Org. Chem. 1990, 55,
5823. Boger, D. L.; Munk, S. A. J . Am. Chem. Soc. 1992, 114, 5487.
Boger, D. L.; Yun, W.; Teegarden, B. R. J . Org. Chem. 1992, 57, 2873.
Boger, D. L.; Palanski, M. S. S. J . Am. Chem. Soc. 1992, 114, 9318.
Boger, D. L.; Yun, W. J . Am. Chem. Soc. 1994, 116, 5523. Boger, D.
L.; Yun, W. J . Am. Chem. Soc. 1994, 116, 7996. Boger, D. L.; McKie,
J . A. J . Org. Chem. 1995, 60, 1271. Boger, D. L.; Yun, W.; Han, N.;
J ohnson, D. S. Bioorg. Med. Chem. 1995, 3, 611. Boger, D. L.; Yun,
W.; Cai, H.; Han, N. Bioorg. Med. Chem. 1995, 3, 761. Boger, D. L.;
Han, N. Bioorg. Med. Chem. 1997, 5, 233. Boger, D. L.; McKie, J . A.;
Boyce, C. W. Synlett 1997, 515. Boger, D. L.; Boyce, C. W.; Garbaccio,
R. M.; Searcey, M. Tetrahedron Lett. 1998, 39, 2227. Boger, D. L.;
Boyce. C. W.; Garbaccio, R. M.; Searcey, M.; J in, Q. Synthesis 1999,
1505.
(17) Boger, D. L.; Mesini, P. J . Am. Chem. Soc. 1994, 116, 11335.
Boger, D. L.; Mesini, P. J . Am. Chem. Soc. 1995, 117, 11647.
(18) Boger, D. L.; Turnbull, P. J . Org. Chem. 1997, 62, 5849.
(19) Boger, D. L.; Turnbull, P. J . Org. Chem. 1998, 63, 8004.
(20) Boger, D. L.; Boyce, C. W. J . Org. Chem. 2000, 65, 4088.
(21) Boger, D. L.; Hughes, T. V.; Hedrick, M. P. J . Org. Chem. 2001,
66, 2207.
(22) For C3 substitution of the CPI alkylation subunit, see: Amish-
iro, N.; Okamoto, A.; Okabe, M.; Saito, H. Bioorg. Med. Chem. 2000,
8, 1195.
(14) Boger, D. L.; McKie, J . A.; Cai, H.; Cacciari, B.; Baraldi, P. G.
J . Org. Chem. 1996, 61, 1710.
(15) Boger, D. L.; Han, N.; Tarby, C. M.; Boyce, C. W.; Cai, H., J in,
Q. J . Org. Chem. 1996, 61, 4894. Boger, D. L.; Boyce, C. W.; J ohnson,
D. S. Bioorg. Med. Chem. Lett. 1997, 7, 233.
(23) Boger, D. L.; Garbaccio, R. M.; J in, Q. J . Org. Chem. 1997, 62,
8875.
(16) Boger, D. L.; J enkins, T. J . J . Am. Chem. Soc. 1996, 118, 8860.

C3-Substituted CBI Analogues of CC-1065 and the Duocarmycins
J . Org. Chem., Vol. 66, No. 15, 2001 5165
Sch em e 1
Sch em e 2
Sch em e 3
moval of either the MOM ether or N-Boc protecting
groups to afford alcohol 21 in good yield.
Although metalation could be accomplished at this
stage by treatment of primary alcohol 21 with excess
t-BuLi, higher yields were obtained by utilizing the
corresponding acetate 22 (Ac2O, pyridine, 93%). Directed
lithiation of acetate 22 at C4 was found to be most
efficiently accomplished by treatment with t-BuLi (4
equiv) for 4 h in Et2O at -78 °C. Reaction of the resultant
aryllithium 23 with hexachloroethane resulted in ef-
ficient chloride introduction, providing the alcohol 24
(70%) following hydrolysis of the residual acetate by
quench of the reaction with 3 M aqueous LiOH.
With the desired C4-substituted intermediates in hand,
activation of the primary alcohol (MsCl, Et3N, 88-99%)
afforded the key intermediates 29-32 (Scheme 3). Mild
acid-catalyzed deprotection of the MOM ether in 28-32
(HCl, i-PrOH, THF), followed by in situ spirocyclization
of the resultant phenol by quench of the reaction with
10% aqueous NaHCO3 directly afforded the ring closed,
C3-substituted N-Boc-CBI derivatives 5-9 (46-77%). In
initial studies, this two-step conversion of 28-32 to 5-9
was accomplished in a stepwise fashion with isolation
and characterization of the intermediate phenols followed
by DBU-promoted spirocyclization (75-95%), but the
more convenient single-step conversion was adopted as
the work progressed.
X-r a y Cr ysta l Str u ctu r es. Central to understanding
the reactivity and reaction regioselectivity of the alky-
lation subunit analogues has been the careful comparison
of their X-ray structures.13,16-18,21,24-26 Consequently, X-
ray crystal structures of the F-, Cl-, Br-, and Me-
substituted CBI analogues were secured as the N-meth-
oxycarbonyl derivatives 33-36, respectively (Scheme 4).24
Unlike 5-7 and 9, the N-Boc derivative of the C3-iodo-
CBI (8) crystallized and was analyzed directly.24
Introduction of the C4 bromine substituent initially
proved to be more challenging, as known bromination
reagents (NBS, Br2, 1,2-dibromoethane, and cyanogen
bromide) failed to provide 25. This unanticipated obstacle
was addressed employing a novel bromine source suitable
for reaction with a hindered aryllithium intermediate.
Thus, the sterically unencumbered 1-bromophenylacety-
lene, envisaged to undergo rapid lithium-halogen ex-
change with the substrate, proved remarkably effective
at C4 bromination of 23 and resulted in the isolation of
25 (68%) following in situ saponification. Similarly, intro-
duction of the corresponding C4 iodine substituent was
accomplished initially through reaction of 23 with 1-chloro-
2-iodoethane, albeit in modest conversions (18%). How-
ever, an analogous use of 1-iodophenylacetylene afforded
the desired 26 in substantially higher yield (68%) fol-
lowing the saponification of the remaining acetate.
Structural analysis of this series revealed several
important features. First, the torsional angle ø1, which
has been shown to be indicative of the extent of vinylo-
gous amide conjugation,25 is strongly perturbed from that
of the parent unsubstituted N-CO2Me-CBI (Figure 4).
The steric interaction of the C3-substituent with the N2-
carbamate results in a twist in ø1, the magnitude of which
was found to smoothly increase as the size of the C3
Initial attempts to install the C4 methyl substituent
by reacting aryllithium 23 with CH3I proved unsuccess-
ful. Consequently, introduction of the C4 methyl sub-
stituent was accomplished by Stille coupling of aryl iodide
26 with Sn(CH3)4 (Pd(PPh3)4, HMPA, 70 °C, 93%) to
afford 27 in excellent yield (Scheme 2). To complete the
series, reaction of aryllithium 23 with (PhSO2)2NF pro-
vided the C4 fluoride 28 (42%). In this case, not only was
the acetate cleaved during reaction, but the isolated
product 28 was the benzenesulfonyl derivative of the
primary alcohol. Though unintended, this intermediate
was ideally functionalized for eventual spirocyclization
circumventing the need for subsequent activation of the
expected alcohol.
(24) The author has deposited the atomic coordinates for the X-ray
structures with the Cambridge Crytallographic Data Centre, and they
have been allocated the following deposition numbers: 33, 160273; 34,
160278; 35, 160705; 8, 160274; 36, 160276; 41, 160703; 43, 160704;
44, 160272.
(25) Boger, D. L.; Garbaccio, R. M. Bioorg. Med. Chem. 1997, 5, 263.
Boger, D. L.; Garbaccio, R. M. Acc. Chem. Res. 1999, 32, 1043.

5166 J . Org. Chem., Vol. 66, No. 15, 2001
Boger et al.
F igu r e 5. Solvolysis study (UV spectra) of 9 in 50% CH3OH-
aqueous buffer (pH 2, 39:1 (v/v) 0.2 M boric acid-0.5 M citric
acid-0.1 M Na3PO4). For clarity, UV traces at only a few time
points are shown: t ) 0, 18, 43, 65, 92, 141, 218, and 367 h.
F igu r e 4.
Sch em e 4
advance of the work accurately depicted the structural
trends and the optimized AM1 structures were found to
be in remarkably good agreement with even the magni-
tude of the trends observed in the X-ray structures.
Solvolysis: Rea ctivity. The solvolysis rate of cyclo-
propyl ring opening has provided much information
regarding the relationship between chemical stability and
biological potency.12,25 With notable exceptions,16-20,23,27
the alkylation subunit analogues have generally proven
stable to solvolysis at pH 7 and consequently have been
studied at more acidic pH (pH 2-3) where rates for an
acid-catalyzed solvolysis are measurable. In cases where
a pH 7 solvolysis reactivity has been measurable, the
relative solvolysis reactivities for different alkylation
subunits at pH 2-3 versus 7 have not been altered. Thus,
it is not surprising that assessed reactivities at pH 2-3,
which typically correlate with relative reactivities at pH
7, were found to be good predictors of biological potency.
However, in the one exception of a series of simple
derivatives of an iso-CI alkylation subunit,27 the relative
reactivity inverted between pH 3 and 7. These results
along with a study of the pH rate profile28 of the reactive
alkylation subunits 13-1517-19 and CPyI20 have indicated
that solvolysis mechanisms switch from one that is acid-
catalyzed at pH 2-3/4 to one that is uncatalyzed at pH
7. Consequently, the solvolysis behavior of the halogen-
substituted CBI series proved especially interesting.
Clear in the initial handling of the materials, they
possessed a managable solvolysis reactivity at pH 7 as
well as pH 2. Moreover, their relative reactivities inverted
at the two pH conditions indicative of a change in
solvolysis mechanism. Thus, the solvolysis of the C3-
substituted N-Boc-CBI derivatives 5-9 were examined
at pH 2 (50% CH3OH-buffer) and pH 7 (50% CH3OH-
buffer), and the progress of the reaction was followed
spectrophotometrically by UV (see Figure 5 for a repre-
sentative series of UV spectra). The rates of solvolysis
are summarized in Table 1.
halogen substituent becomes larger. By contrast, the ø2
dihedral angle is unperturbed by the structural changes
indicating that the carbamate N2-conjugation is main-
tained at the expense of the vinylogous amide conjuga-
tion. Notably, the X-ray crystal structure of the fluoro
derivative 33 shows that the methoxycarbonyl group is
rotated 180° compared to its orientation in the X-ray
crystal structures of 8 and 34-36.26
In the studies conducted to date, the most diagnostic
indication of the extent of vinylogous amide conjugation
has been derived from the N2-C2a bond length (r).
Comparison of the methyl-substituted CBI derivative 36
with N-CO2Me-CBI illustrates a substantial increase in
the N2-C2a bond length (1.414 versus 1.390 Å), sug-
gesting diminished vinylogous amide conjugation. This
difference is likely a result of destabilizing steric interac-
tions between the C3 methyl substituent and the N2-CO2-
Me group resulting in a twist in the ø1 dihedral angle
diminishing the vinylogous amide conjugation resulting
in an extended N2-C2a bond length. Within the limits
of error, the halogen-substituted series exhibit N2-C2a
bond lengths (r) which appear to follow this same trend.
Although they are clearly influenced by the inductive and
electronic nature of the halogen substituent (i.e., versus
36), both the extent of the twist in ø1 and the diagnostic
N2-C2a bond length r increase as the size of the halogen
substituent increases suggesting the vinylogous amide
conjugation decreases through the series (H > F > Cl >
Br > I). Interestingly, modeling (MM2) and computa-
tional (AM1) studies of the analogues 5-9 conducted in
The most significant of these reactivities was the pH
7 solvolysis behavior (Table 1). The C3 methyl derivative
9, unlike N-Boc-CBI (4) itself, exhibited a measurable
reactivity at pH 7. The halogen-substituted analogues
(26) The source of this distinction and its impact on the comparison
interpretations is unknown but should be kept in mind along with the
fact that the N-Boc versus N-CO2Me derivative of the C3 iodo analogue
was utilized.
(27) Boger, D. L.; Garbaccio, R. M. J . Org. Chem. 1999, 64, 8350.
(28) Boger, D. L.; Garbaccio, R. M. J . Org. Chem. 1999, 64, 5666.

C3-Substituted CBI Analogues of CC-1065 and the Duocarmycins
J . Org. Chem., Vol. 66, No. 15, 2001 5167
Ta ble 1. Solvolysis Ra tes of N-Boc-CBI An a logu es (4-9)
w ith Un iver sa l Bu ffer a
agent k (h-1, pH 2) t1/2 (h, pH 2) k (h-1, pH 7) t1/2 (h, pH 7)
4
9
5
6
7
8
5.51 × 10-2
1.02 × 10-2
8.06 × 10-3
5.87 × 10-3
4.68 × 10-3
3.68 × 10-3
12.5
68
stable
stable
900
0.77 × 10-3
1.02 × 10-3
1.89 × 10-3
2.17 × 10-3
>2.17 × 10-3
86
681
118
148
188
367
319
<319b
a
50% CH3OH-aqueous buffer (B(OH)3-citric acid-Na3PO4).
b
Competitive solvolysis and Boc hydrolysis observed at pH 7.
F igu r e 6.
exhibited an even more pronounced pH 7 reactivity
following a smooth trend (I > Br > Cl > F). The analysis
of the iodo analogue 8 suffers from a competitive N2-Boc
hydrolysis complicating the determination of an accurate
solvolysis half-life measurement, but it is clear from the
study that its solvolysis reactivity exceeded that of the
remaining analogues. As detailed later, a pH rate profile
for 6 revealed that the reactions constitute an uncata-
lyzed solvolysis at pH 7.
F igu r e 7. Solvolysis pH-rate profile of 6 with universal
buffer (50% CH3OH-aqueous buffer (B(OH)3-citric acid-Na3-
PO4).
Beautifully, these trends in reactivity reversed at pH
2, indicating a change in solvolysis mechanism from
uncatalyzed to acid-catalyzed solvolysis. All the C3-
substituted CBI analogues were more stable than N-Boc-
CBI (4) itself (t1/2 ) 12.5 h). The most reactive of the
analogues was the methyl substituted CBI 9 (t1/2 ) 68 h)
followed by the halogen derivatives (F > Cl > Br > I). In
part, this reversed order of reactivity may be attributed
to the electron-withdrawing nature of the halogen sub-
stituents, which should inductively disfavor protonation
required of the acid-catalyzed solvolysis. However, even
the C3-methyl-substituted CBI analogue was found to be
more stable than 4, indicating factors fundamental to all
the structures were contributing to this enhanced stabil-
ity. One possible explanation is that the acid-catalyzed
solvolysis reactivity is directly related to the extent of
vinylogous amide conjugation within this series. That is,
the vinylogous amide carbonyl pKb along with the viny-
logous amide conjugation decreases as one moves down
the series and this results in diminished C4 carbonyl
protonation slowing the rate of acid-catalyzed solvolysis.
Similar observations have been made in the pH 3
reactivity of a series of N-substituted CBI derivatives
(37-40, Figure 6)29 and a series of iso-CBI derivatives,27
the latter of which also exhibited the analogous inversion
of reactivity at pH 7 versus pH 3. Importantly, in each
of these cases, it is the increasing pH 7 reactivity of the
uncatalyzed reaction that correlates with diminished
vinylogous amide conjugation.
especially within the pH range 3-6, indicating a change
in mechanism from acid-catalyzed to uncatalyzed sol-
volysis and illustrating that these derivatives are sub-
stantially less stable across this pH range than the
parent N-Boc-CBI. At pH 8 and above, significant com-
petitive N2-carbamate hydrolysis was detected, obscuring
an accurate determination of solvolysis reactivity and
illustrating the general increased reactivity of the halogen-
substituted agents.
Importantly, these observations on the pH 7 reactivity
of 5-9 are consistent with the proposal of a DNA binding-
induced conformational change in 1-3, which twists the
linking N2 amide disrupting the vinylogous amide con-
jugation, providing the necessary and sufficient activation
(catalysis) for a non-acid-catalyzed pH 7-8 DNA alky-
lation reaction.
Solvolysis: Regioselectivity. The acid-catalyzed nu-
cleophilic addition of CH3OH to 5-9 was conducted on a
preparative scale to establish the regioselectivity of
addition. Treatment of 5 with catalytic CF3SO3H (0.12
equiv, CH3OH, 25 °C, 24 h) led to two products in a ratio
of 4:1 (Scheme 5). The major product 41 was shown to
result from CH3OH attack at the more substituted
cyclopropane carbon, regioselectivity distinct from that
observed with the parent N-Boc-CBI (>20:1) which
undergoes exclusive attack at the least substituted
cyclopropane carbon. Confirmation of the structure of 41
was obtained by a single-crystal X-ray structure.24
A
The full pH-rate profile for solvolysis of the chloro
derivative 6 was examined from pH 2-10, (Figure 7). The
rate of solvolysis was shown to decrease by essentially a
factor of 10 in going from pH 2 to 3, confirming that the
solvolysis is acid-catalyzed within this pH range. Above
pH 3, the solvolysis rate remained nearly unchanged,
single enantiomer of this minor ring expansion product
41 was formed upon reaction of optically active 5. Thus,
41 was found to be generated with complete inversion of
the stereochemistry at the reacting center, indicating an
SN2 reaction mechanism. Interestingly, treatment of
analogues 6-9 under these same conditions exclusively
provided the ring expansion products 43-46, whose
structures were confirmed by single-crystal X-ray struc-
(29) Boger, D. L.; Yun, W.; Han, N. Bioorg. Med. Chem. 1995, 3,
1429. Boger, D. L.; Yun, W. J . Am. Chem. Soc. 1994, 116, 5523.

5168 J . Org. Chem., Vol. 66, No. 15, 2001
Boger et al.
Ta ble 2. Resolu tion on Ch ir a lcel OD Colu m n
Sch em e 5
agent
R
21
24
25
26
27
1.15
1.46
1.66
1.98
1.80
Ta ble 3. In Vitr o Cytotoxic Activity
natural enantiomers unnatural enantiomers
compd IC50, µM (L1210)
compound
IC50, µM (L1210)
(+)-4
(-)-5
(+)-6
(+)-7
(+)-8
(+)-9
0.08
0.2
2.1
1.4
1.2
3.1
ent-(-)-4
ent-(+)-5
ent-(-)-6
ent-(-)-7
ent-(-)-8
ent-(-)-9
0.9
3.7
3.9
4.7
4.2
7.4
cases, the natural enantiomers were shown to be more
potent than the unnatural enantiomers although the
distinctions are generally not large. The fluoro derivative
5 shows both the best activity, as well as the greatest
difference in activity between enantiomers. This behavior
mirrors that of the parent unsubstituted CBI derivative,
although it is an order of magnitude less potent, whereas
6-9 exhibit only a subtle difference between the enan-
tiomers (ca. 2×) and all are 100-fold less potent than 4.
To date, the stability of the CC-1065 alkylation subunit
analogues at pH 2-3 has been a useful tool for predicting
biological potency.12 In general, the trend has shown that
a greater stability to solvolysis translates into a deriva-
tive that is more cytotoxic, presumably the consequence
of the chemically more stable derivatives more effectively
reaching their biological target. The pH 2-3 solvolysis
reactivity has been employed since pH 7 reactivity
typically has been immeasurable. With one notable
exception in cases where the comparisons could be
made,27 the pH 2-3 relative reactivity has paralleled that
observed at pH 7 establishing the validity of this gener-
alization. However, the results highlighted herein, where
there is a clear reordering of the reactivities between pH
2-3 and 7, which is a consequence of the change in
mechanism from acid-catalyzed to uncatalyzed solvolysis,
suggest that it is the pH 7 relative stability (4 > 5-9),
and not that at pH 2-3 (4 < 5-9), that correlates with
biological potency. Thus, in the series of halogen deriva-
tives, (-)-5 exhibits both the most potent activity and
the greatest stability at pH 7. In addition, 5 is the lone
member of the series that also exhibits any of the
regioselective reactivity observed with the parent system
4, a behavior that may also account for its enhanced
cytotoxic potency relative to the other derivatives in the
series. However, there are a number of alternative
explanations that may also account for the observations.
The greatest activity is also observed with derivatives
that exhibit the smallest ø1 dihedral angle (4 > 5 > 6-9)
suggesting 6-9, and to a lesser extent 5, may bind in
the minor grove more poorly, and comparably, due to the
comparable twist in the carbamate linkage. Regardless
of the origin of the effects, C3 substitution substantially
diminishes cytotoxic potency. To our knowledge, only one
other study of C3 substitution of a stable alkylation
subunit has been described.22 Although the evaluations
detailed were limited to cytotoxic potency and in vivo
antitumor efficacy, similar trends in cytotoxic potency
were observed where C3 substitution resulted in 10-100
fold reductions in potency.
tures of 4324 and 4424 and subsequent comparison of the
1H NMR spectra of 45 and 46 with those of the X-ray
determined structures. Notably, single enantiomers of
43-46 were generated using optically active substrates
in reactions that proceed by an analogous SN2 reaction
mechanism. These latter results illustrate clean cleavage
of the C8b-C9a bond with SN2 addition of CH3OH to the
more substituted C9a cyclopropane carbon, and no prod-
uct was detected (>20:1) resulting from the cleavage of
the C8b-C9 bond. Although distinct from the reaction
regioselectivity of N-Boc-CBI, this ring expansion addi-
tion of CH3OH addition is analogous to that observed
with N-Boc-CNA18 and CBIn19 which also exhibit pref-
erential addition at the more hindered cyclopropyl car-
bon, affording similar ring expanded products.
Resolu tion a n d Assign m en t of Absolu te Con fig-
u r a tion . The C3-substituted CBI derivatives were re-
solved using a Chiralcel-OD semipreparative HPLC
column (2 × 25 cm, 7% i-PrOH-hexanes eluent, 12 mL/
min) at the latest synthetic stage possible for each
analogue (Table 2). The Cl, Br, I, and Me derivatives
exhibited the best resolution immediately following the
installation of the key substituent (24-27). The corre-
sponding fluoro derivative did not resolve at any stage
following installation of the fluorine substituent and
required the resolution of 21 and its conversion on to 5.
The absolute configuration of 5-9 was assigned through
the synthesis of authentic (+)-N-CO2Me-CBI18 from this
resolved intermediate 21 (eq 1). Subsequent preparation
of optically active 24-27 and 5-9 from resolved 21 was
then performed to unambiguously assign the absolute
configuration of each analogue.
In Vitr o Cytotoxic Activity. The optically active
derivatives 5-9 were tested for cytotoxic activity against
the L1210 cell line (Table 3). In general, the potency of
the C3-substituted analogues is markedly less than that
of the unsubstituted parent N-Boc-CBI (10-100×). In all

C3-Substituted CBI Analogues of CC-1065 and the Duocarmycins
J . Org. Chem., Vol. 66, No. 15, 2001 5169
in THF-CH3OH (56 mL, 1:1) at -78 °C was treated with
N-iodosuccinimide (NIS, 2.2 g, 9.9 mmol) in THF (2 mL)
followed by TsOH‚H2O (2.5 g, 13.2 mmol) in CH3OH (2 mL).
The reaction mixture was allowed to slowly warm to 0 °C over
4 h and then diluted with 5% aqueous Na2S2O3 and stirred at
25 °C for 15 min. The reaction mixture was diluted with
EtOAc, and the aqueous phase was separated and extracted
twice with EtOAc. The organic layers were combined, dried
(Na2SO4), decanted, and concentrated in vacuo. Flash chro-
matography (SiO2, 6 × 20 cm, 5% EtOAc-hexanes) afforded
18 as a pale yellow solid (2.2 g, 77%): mp 85-87 °C; 1H NMR
(250 MHz, CDCl3) δ 8.20 (d, J ) 8.0 Hz, 1H), 8.06 (d, J ) 6.9
Hz, 1H), 8.04 (s, 1H), 7.55 (dd, J ) 6.9, 1.1 Hz, 1H), 7.42 (dd,
J ) 8.0, 1.1 Hz, 1H), 7.25 (s, 1H), 5.46 (s, 2H), 3.57 (s, 3H),
1.58 (s, 9H); 13C NMR (62.5 MHz, CDCl3) δ 153.9, 152.8, 138.4,
134.9, 131.5, 128.7, 124.8, 123.9, 122.6, 102.6, 94.9, 82.0, 81.3,
56.8, 28.5; IR (film) νmax 3384, 2977, 1733, 1495 cm-1; FAB-
HRMS (NBA/NaI) m/z 429.0449 (M+, C17H20INO4 requires
429.0437). Anal. Calcd for C17H20INO4: C, 47.57; H, 4.70; N,
3.26. Found: C, 47.50; H, 4.82; N, 3.14.
Con clu sion s
A series of C3-substituted N-Boc-CBI derivatives 5-9
were prepared through a directed metalation of the seco-
CBI core. Introduction of the fluoro and chloro substit-
uents was accomplished with known electrophiles, whereas
the installation of the bromo and iodo substituents
required use of a novel reagent for effective halogenation
of a hindered aryllithium intermediate. Thus, the steri-
cally unencumbered 1-bromo- and 1-iodophenylacetylenes
proved remarkably successful for the nucleophilic halo-
genation and should prove to be generally applicable to
similar lithium-halogen exchange reactions beyond those
we describe. The single X-ray crystal structures of these
derivatives, especially those of the halogen series, high-
lighted a substantial perturbation in the vinylogous
amide conjugation (r, N2-C2a bond length) and the
dihedral angle ø1, with r and ø1 smoothly increasing as
the size of the C3 substituent increases. The solvolysis
reactivity of the series proved especially interesting. At
pH 7, the C3 substituted derivatives were substantially
more reactive than N-Boc-CBI (4) itself and the halogen
series smoothly followed an expected trend of increasing
reactivity with diminished vinylogous amide stabilization
(I > Br > Cl > F > H). Beautifully, this trend reversed
for solvolysis reactivity at pH 2 and is indicative of a
change in solvolysis reaction mechanism from one that
is uncatalyzed at pH 7 to one that is acid-catalyzed at
pH 2-3. A full pH-rate profile for the solvolysis reaction
of the chloro derivative 6 confirmed this behavior,
indicating that the acid-catalyzed reaction is observed at
pH 2-3 but that the uncatalyzed reaction dominates the
rate at pH >3-7. Similarly interesting, the clean SN2
addition of CH3OH to the more hindered carbon of the
cyclopropyl ring with ring expansion was shown to be
preferred for all the C3-substituted CBI derivatives, an
observation that is in contrast to the exclusive regiose-
lectivity exhibited by the unsubstituted N-Boc-CBI (>20:
1) for addition to the least substituted cyclopropane
carbon. Finally, the C3-substituted CBI derivatives were
found to be 10-100× less cytotoxic than the parent
system, with the fluoro-substituted derivative exhibiting
the most potent activity. This most likely may be at-
tributed to its greater similarity to N-Boc-CBI (4) in pH
7 reactivity, structure, and inherent regioselectivity of
reaction.
2-[(N-ter t-Bu tyloxyca r bon yl)-N-(2-p r op en -1-yl)a m in o]-
1-iod o-4-(m eth oxym eth oxy)n a p h th a len e (19). A solution
of 18 (3.5 g, 8.2 mmol) in THF (15 mL) was treated with allyl
bromide (3.6 mL, 41.1 mmol) followed by a solution of Bu4NI
(0.15 g, 0.41 mmol) in THF (1.5 mL). NaH (0.49 g, 12.3 mmol,
60% dispersion in mineral oil) was added slowly to the reaction
mixture at 0 °C. The reaction mixture was allowed to warm
to 25 °C over 6 h, diluted with EtOAc, and poured into
saturated aqueous NH4Cl. The aqueous phase was separated
and extracted twice with EtOAc. The organic layers were
combined, dried (Na2SO4), decanted, and concentrated in
vacuo. Flash chromatography (SiO2, 5 × 15 cm, 5% EtOAc-
hexanes) afforded 19 as an off-white solid (3.8 g, 99%): mp
1
61-63 °C; H NMR (250 MHz, CDCl3, major rotamer) δ 8.23
(m, 2H), 7.57 (m, 2H), 6.97 (s, 1H), 6.01 (m, 1H), 5.37 (m, 2H),
5.08 (m, 2H), 4.60 (m, 1H), 3.83 (m, 1H), 3.53 (s, 3H), 1.35 (s,
9H); 13C NMR (62.5 MHz, CDCl3, major rotamer) δ 153.6,
153.4, 142.9, 135.2, 133.5, 132.7, 128.3, 126.2, 125.3, 122.2,
117.9, 117.4, 110.3, 95.9, 94.7, 80.1, 56.1, 52.2, 28.2; IR (film)
νmax 2976, 1702, 1591, 1390 cm-1; MALDIHRMS (DHB) m/z
492.0626 (M+ + Na, C20H24INO4 requires 492.0648). Anal.
Calcd for C20H24INO4: C, 51.18; H, 5.15; N, 2.98. Found: C,
51.33; H, 5.29; N, 2.93.
3-(t er t -Bu t yloxyc a r b on yl)-5-(m e t h oxym e t h oxy)-1-
[(2′,2′,6′,6′-tetr am eth ylpiper idin o)oxy]m eth yl-1,2-dih ydr o-
3H-ben z[e]in d ole (20). A solution of 19 (3.9 g, 8.3 mmol) in
benzene (380 mL) was treated with TEMPO (3.9 g, 25 mmol)
followed by Bu3SnH (2.3 mL, 8.7 mmol). The solution was
warmed at 70 °C for 30 min, and then an additional 1.0 equiv
Bu3SnH (2.2 mL, 8.3 mmol) was added. An additional 1.5 equiv
of TEMPO (1.9 g, 12.4 mmol) was added after 30 min (1 h total
reaction time), and the reaction mixture was stirred for
another 30 min. A final 1.0 equiv of Bu3SnH was added after
1.5 h of reaction. The reaction mixture was allowed to stir for
1 h, cooled to 25 °C, and poured into saturated aqueous NaCl.
The aqueous phase was separated and extracted twice with
EtOAc. The organic layers were combined, dried (Na2SO4),
decanted, and concentrated in vacuo. Flash chromatography
(SiO2, 6 × 20 cm, 0-5% EtOAc-hexanes gradient) afforded
20 as an orange oil (2.9 g, 70%): 1H NMR (400 MHz, CDCl3)
δ 8.22 (d, J ) 8.0 Hz, 1H), 7.90 (br s, 1H), 7.72 (d, J ) 8.0 Hz,
1H), 7.47 (app t, J ) 7.1 Hz, 1H), 7.33 (app t, J ) 7.5 Hz, 1H),
5.42 (m, 2H), 4.30 (d, J ) 11.0 Hz, 1H), 4.08 (m, 2H), 3.81 (m,
2H), 3.57 (s, 3H), 1.62 (s, 9H), 1.45-0.86 (m, 18H); 13C NMR
(100 MHz, CDCl3) δ 152.8, 151.9, 140.3, 129.9, 126.3, 122.3
(3C), 121.8, 116.2, 98.3, 94.3, 79.9, 59.1, 55.8, 51.9, 38.9, 37.8,
32.5, 27.9, 19.4, 16.4; IR (film) νmax 2930, 1703, 1584, 1381
cm-1; FABHRMS (NBA/NaI) m/z 499.3183 (M+, C29H42N2O5
requires 499.3172).
The observations made with this series of CBI ana-
logues have important implications on the source of
catalysis for the DNA alkylation by 1-3. They demon-
strate that disruption of the vinylogous amide conjuga-
tion by a twist in the linking amide (ø1) provides sufficient
activation (catalysis) for nucleophilic attack to account
for an uncatalyzed (versus acid-catalyzed) DNA alkyla-
tion reaction at pH 7-8. This is consistent with a number
of related observations25,29,30 and with the proposal that
the DNA alkylation catalysis is derived from a DNA
binding-induced conformational change in the agents that
twists the linking amide (ø1) resulting in a diminished
vinylogous amide conjugation activating them for nu-
cleophilic attack.25
Exp er im en ta l Section
N-(ter t-Bu tyloxycar bon yl)-1-iodo-4-(m eth oxym eth oxy)-
2-n a p h th yla m in e (18). A solution of 1723 (2.0 g, 6.6 mmol)
3-(ter t-Bu tyloxyca r bon yl)-1-(h yd r oxym eth yl)-5-(m eth -
oxym eth oxy)-1,2-d ih yd r o-3H-ben z[e]in d ole (21). A solu-
tion of 20 (2.9 g, 5.8 mmol) in AcOH-THF-H2O (180 mL, 3:1:
1) was treated with activated Zn dust (1.0 g, 15 mmol) and
warmed at 70 °C for 2 h. An additional 0.5 g of Zn dust was
(30) Boger, D. L.; Santilla´n, A., J r.; Searcey, M.; J in, Q. J . Am. Chem.
Soc. 1998, 120, 11554. Boger, D. L.; Santilla´n, A., J r.; Searcey, M.;
J in, Q. J . Org. Chem. 1999, 64, 5241.

5170 J . Org. Chem., Vol. 66, No. 15, 2001
Boger et al.
added, and the reaction mixture was stirred for another 2 h.
The reaction mixture was cooled to 25 °C and filtered, and
the volatiles were removed under reduced pressure. The
resultant residue was rediluted with EtOAc and poured into
saturated aqueous NaCl. The aqueous phase was separated
and extracted twice with EtOAc. The organic layers were
combined, dried (Na2SO4), decanted, and concentrated in
vacuo. Flash chromatography (SiO2, 5 × 15 cm, 20-30%
EtOAc-hexanes gradient) afforded 21 as a white solid (1.5 g,
1-Bromophenylacetylene (197 mg, 1.1 mmol) was added neat
to a solution of aryllithium 23 (0.27 mmol). Flash chromatog-
raphy (SiO2, 2 × 15 cm, 15-25% EtOAc-hexanes gradient)
afforded 25 as an off-white foam (81 mg, 68%): 1H NMR (400
MHz, CDCl3) δ 8.20 (d, J ) 8.2 Hz, 1H), 7.77 (d, J ) 8.2 Hz,
1H), 7.52 (m, 1H), 7.45 (m, 1H), 5.33 (d, J ) 5.8 Hz, 1H), 5.27
(d, J ) 5.8 Hz, 1H), 4.51 (d, J ) 11.7 Hz, 1H), 4.17 (dd, J )
11.7, 7.6 Hz, 1H), 3.95 (m, 1H), 3.80 (m, 1H), 3.75 (s, 3H), 3.61
(dd, J ) 11.3, 6.9 Hz, 1H), 2.03 (s, 1H), 1.53 (s, 9H); 13C NMR
(100 MHz, CDCl3) δ 154.9, 152.2, 141.9, 129.4, 127.4 (2C),
126.6, 125.4, 123.6, 123.4, 107.8, 100.7, 81.7, 63.5, 58.3, 56.3,
44.4, 28.1; IR (film) νmax 3453, 2977, 1708, 1364 cm-1; ESIMS
m/z 438 (M+ + H, C20H24BrNO5 requires 438).
1
72%): mp 96-98 °C; H NMR (400 MHz, CDCl3) δ 8.23 (d, J
) 7.9 Hz, 1H), 7.92 (br s, 1H), 7.73 (d, J ) 7.6 Hz, 1H), 7.48
(app t, J ) 7.0 Hz, 1H), 7.34 (app t, J ) 7.6 Hz, 1H), 5.42 (s,
2H), 4.21 (br s, 1H), 4.12 (m, 1H), 3.94 (dd, J ) 10.3, 3.5 Hz,
1H), 3.83 (m, 1H), 3.76 (dd, J ) 10.3, 7.3 Hz, 1H), 3.56 (s, 3H),
1.61 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 153.7, 152.8, 141.8,
130.7, 127.2 (2C), 122.6, 115.9, 98.9, 94.9, 81.9, 64.6, 56.6, 52.4,
41.4, 28.5; IR (film) νmax 3452, 2975, 1698, 1381 cm-1; FAB-
HRMS (NBA/NaI) m/z 359.1744 (M+, C20H25NO5 requires
359.1733). Anal. Calcd for C20H25NO5: C, 66.83; H, 7.01; N,
3.90. Found: C, 66.74; H, 6.84; N, 3.92.
Natural (-)-(1S)-25: [R]25 -59 (c 1.21, THF).
D
ent-(+)-(1R)-25: [R]25 +64 (c 1.12, THF).
D
3-(ter t-Bu tyloxyca r bon yl)-1-(h yd r oxym eth yl)-4-iod o-5-
(m eth oxym eth oxy)-1,2-dih ydr o-3H-ben z[e]in dole (26). 1-Io-
dophenylacetylene (212 mg, 0.93) was added neat to a solution
of aryllithium 23 (0.23 mmol). Flash chromatography (SiO2, 2
× 15 cm, 15-25% EtOAc-hexanes gradient) afforded 26 as
an off-white foam (78 mg, 68%): 1H NMR (400 MHz, CDCl3)
δ 8.19 (d, J ) 8.2 Hz, 1H), 7.76 (d, J ) 8.2 Hz, 1H), 7.51 (m,
1H), 7.43 (m, 1H), 5.31 (d, J ) 5.8 Hz, 1H), 5.24 (d, J ) 5.5
Hz, 1H), 4.52 (d, J ) 11.7 Hz, 1H), 4.17 (dd, J ) 11.7, 7.5 Hz,
1H), 3.94 (m, 1H), 3.78 (m, 1H), 3.77 (s, 3H), 3.62 (m, 1H),
2.09 (br s, 1H), 1.55 (s, 9H); 13C NMR (100 MHz, CDCl3) δ
155.7, 155.2, 145.1, 130.5, 127.8, 126.9, 126.5, 125.5, 124.0,
123.6, 101.2, 83.9, 81.9, 63.7, 58.6, 56.4, 44.9, 28.3; IR (film)
Natural-(-)-(1S)-21: [R]25 -1.7 (c 0.70, THF).
D
ent-(+)-(1R)-21: [R]25 +1.9 (c 0.78, THF).
D
1-(Acetoxym eth yl)-3-(ter t-bu tyloxyca r bon yl)-5-(m eth -
oxym eth oxy)-1,2-d ih yd r o-3H-ben z[e]in d ole (22). A solu-
tion of 21 (0.25 g, 0.70 mmol) in CH2Cl2 (10 mL) was treated
with Ac2O (0.33 mL, 3.5 mmol) followed by pyridine (0.28 mL,
3.5 mmol). The reaction mixture was stirred at 25 °C for 18 h
and poured into saturated aqueous NaCl. The aqueous phase
was separated and extracted twice with EtOAc. The organic
layers were combined, dried (Na2SO4), decanted, and concen-
trated in vacuo. Flash chromatography (SiO2, 2.5 × 15 cm,
10% EtOAc-hexanes) afforded 22 as a white solid (0.26 g,
ν
max 3432, 2977, 1708, 1359 cm-1. Anal. Calcd for C20H24INO5:
C, 49.50; H, 4.98; N, 2.89. Found: C, 49.26; H, 4.92; N, 2.67.
Natural (-)-(1S)-26: [R]25 -16 (c 0.78, THF).
D
ent-(+)-(1R)-26: [R]25 +15 (c 0.98, THF).
D
1
93%): mp 97-99 °C; H NMR (400 MHz, CDCl3) δ 8.21 (d, J
3-(ter t-Bu tyloxyca r bon yl)-1-(h yd r oxym eth yl)-5-(m eth -
oxym eth oxy)-4-m eth yl-1,2-dih ydr o-3H-ben z[e]in dole (27).
A solution of Pd(PPh3)4 (4.5 mg, 3.9 µmol) dissolved in degassed
HMPA (2 mL) was added to a sample of aryl iodide 26 (19
mg, 39 mmol) followed by SnMe4 (14 µL, 79 µmol). The reaction
mixture was warmed at 65 °C, stirred for 72 h before being
diluted with H2O and poured into Et2O. The aqueous phase
was separated and extracted twice with Et2O. The organic
layers were combined, dried (Na2SO4), decanted, and concen-
trated in vacuo. Flash chromatography (SiO2, 1.5 × 15 cm,
15-25% EtOAc-hexanes) afforded 27 as a colorless oil (16.4
mg, 93%): 1H NMR (400 MHz, CDCl3) δ 8.12 (d, J ) 7.9 Hz,
1H), 7.75 (d, J ) 7.6 Hz, 1H), 7.42 (m, 2H), 5.22 (d, J ) 5.9
Hz, 1H), 5.14 (d, J ) 5.9 Hz, 1H), 4.50 (d, J ) 11.4 Hz, 1H),
4.12 (dd, J ) 11.4, 3.8 Hz, 1H), 3.94 (dd, J ) 11.0, 4.3 Hz,
1H), 3.79 (dd, J ) 11.2, 6.8 Hz, 1H), 3.69 (s, 3H), 3.56 (dd, J
) 11.2, 6.9 Hz, 1H), 2.38 (s, 3H), 1.75 (br s, 1H), 1.52 (s, 9H);
13C NMR (125 MHz, CDCl3) δ 155.4, 152.7, 143.1, 129.1, 126.7,
126.4, 124.7, 124.0, 123.4, 123.3, 121.5, 100.3, 81.3, 64.1, 58.1,
56.1, 43.8, 28.5, 14.9; IR (film) νmax 3452, 2930, 1707, 1369
cm-1; FABHRMS (NBA/NaI) m/z 373.1893 (M+, C21H27NO5
requires 373.1889).
) 8.2 Hz, 1H), 7.91 (br s, 1H), 7.78 (d, J ) 8.5 Hz, 1H), 7.49
(m, 1H), 7.34 (m, 1H), 5.41 (s, 2H), 4.56 (m, 1H), 4.18 (br s,
1H), 4.06 (m, 1H), 3.95-3.83 (m, 2H), 3.54 (s, 3H), 2.10 (S,
3H), 1.62 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 171.2, 154.2,
152.6, 140.4, 130.7, 127.5, 123.3, 123.1, 122.7 (2C), 115.8, 99.6,
94.9, 81.9, 65.8, 56.5, 52.4, 37.7, 28.6, 21.1; IR (film) νmax 2975,
1697, 1381, 1333 cm-1; MALDIHRMS (DHB) m/z 424.1736 (M+
+ Na, C22H27NO6 requires 424.1736).
Natural (+)-(1S)-22: [R]25 +9 (c 0.19, THF).
D
ent-(-)-(1R)-22: [R]25 -11 (c 0.11, THF).
D
Dir ected Or th o-Meta la tion a n d Su bsequ en t Ha loge-
n a tion of 22. Gen er a l P r oced u r e. A solution of 22 (1.0
equiv) in Et2O (0.06 M) at -78 °C was treated dropwise with
t-BuLi (4.0 equiv) as a 1.8 M solution in pentane. The halogen
source (4.0 equiv) was added after 4 h of stirring, and the
reaction mixture was allowed to slowly warm to 0 °C. Excess
3 M aqueous LiOH was added and the mixture was allowed
to stir and warm to 25 °C over 1 h. The mixture was diluted
with EtOAc and poured into saturated aqueous NH4Cl. The
aqueous phase was separated and extracted twice with EtOAc.
The organic layers were combined, dried (Na2SO4), decanted,
and concentrated in vacuo.
Natural (-)-(1S)-27: [R]25 -96 (c 0.44, THF).
D
ent-(+)-(1R)-27: [R]25 +98 (c 0.45, THF).
3-(ter t-Bu tyloxyca r bon yl)-4-ch lor o-1-(h yd r oxym eth yl)-
5-(m eth oxym eth oxy)-1,2-d ih yd r o-3H-ben z[e]in d ole (24).
Hexachloroethane (137 mg, 0.58 mmol) was added to aryl-
lithium 23 (0.15 mmol) as a solution in Et2O (0.5 mL). Flash
chromatography (SiO2, 2 × 15 cm, 15-25% EtOAc-hexanes
gradient) afforded 24 as an off-white foam (40 mg, 70%): 1H
NMR (400 MHz, CDCl3) δ 8.16 (d, J ) 7.8 Hz, 1H), 7.75 (d, J
) 7.6 Hz, 1H), 7.49-7.41 (m, 2H), 5.31 (d, J ) 5.7 Hz, 2H),
5.26 (d, J ) 5.9 Hz, 1H), 4.49 (d, J ) 11.6 Hz, 1H), 3.93 (dd,
J ) 10.8, 4.3 Hz, 1H), 3.78 (dd, J ) 10.8, 6.8 Hz, 1H), 3.71 (s,
3H), 3.57 (m, 1H), 1.50 (s, 9H); 13C NMR (62.5 MHz, CDCl3) δ
155.1, 150.9, 140.5, 128.9, 127.5 (2C), 126.6, 125.5, 123.6 (2C),
117.8, 100.6, 81.8, 63.6, 58.4, 56.4, 44.3, 28.3; IR (film) νmax
3454, 2932, 1704, 1366 cm-1; MALDIHRMS (DHB) m/z
416.1223 (M+ + Na, C20H24ClNO5 requires 416.1241).
D
1-[[(Ben zen esu lfon yl)oxy]m eth yl]-3-(ter t-bu tyloxyca r -
bon yl)-4-flu or o-5-(m eth oxym eth oxy)-1,2-dih ydr o-3H-ben z-
[e]in d ole (28). (PhSO2)2NF (315 mg, 1.0 mmol) was added to
a solution of aryllithium 23 (0.25 mmol) as a solution in THF
(1.0 mL). Flash chromatography (SiO2, 2 × 15 cm, 10%
EtOAc-hexanes) afforded 28 as an orange oil (55 mg, 42%):
1H NMR (500 MHz, CDCl3) δ 8.10 (m, 1H), 7.74 (d, J ) 8.2
Hz, 2H), 7.51 (m, 2H), 7.39 (m, 4H), 5.32 (d, J ) 5.5 Hz, 1H),
5.30 (d, J ) 5.5 Hz, 1H), 4.36 (m, 2H), 4.09 (dd, J ) 11.5, 8.2
Hz, 1H), 3.99 (dd, J ) 10.4, 8.2 Hz, 1H), 3.77 (m, 1H), 3.65 (s,
3H), 1.53 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 153.2, 144.9,
142.9, 140.6 (d, J ) 10.6 Hz), 135.5, 133.9, 131.9 (d, J ) 12.5
Hz), 128.5 (d, J ) 178.5 Hz), 127.0, 126.9 (d, J ) 5.8 Hz), 126.4,
125.9, 123.2 (d, J ) 6.7 Hz), 122.6, 121.9 (d, J ) 1.9 Hz), 99.8
(d, J ) 7.7 Hz), 81.9, 69.8, 57.9, 54.5, 40.4, 28.2; 19F NMR (376
Natural (-)-(1S)-24: [R]25 -95 (c 1.35, THF).
D
ent-(+)-(1R)-24: [R]25 +99 (c 1.15, THF).
D
MHz, C6D6) δ -134.4 (s); IR (film) νmax 2977, 1712, 1385 cm-1
;
4-Br om o-3-(ter t-bu tyloxyca r bon yl)-1-(h yd r oxym eth yl)-
5-(m eth oxym eth oxy)-1,2-d ih yd r o-3H-ben z[e]in d ole (25).
MALDIHRMS (DHB) m/z 540.1473 (M+ + Na, C26H28FNO7S
requires 540.1468).

C3-Substituted CBI Analogues of CC-1065 and the Duocarmycins
J . Org. Chem., Vol. 66, No. 15, 2001 5171
Natural (-)-(1S)-28: [R]25 -95 (c 0.16, THF).
reaction mixture was quenched with the addition of excess
aqueous 10% NaHCO3, stirred for 30 min, diluted with EtOAc,
and poured into aqueous 10% NaHCO3. The aqueous phase
was separated and extracted twice with EtOAc. The organic
layers were combined, dried (Na2SO4), decanted, and concen-
trated in vacuo.
D
ent-(+)-(1R)-28: [R]25 +94 (c 0.14, THF).
D
Mesyla tion of Alcoh ols 24-27. Gen er a l P r oced u r e. A
solution of the alcohol (1.0 equiv) in CH2Cl2 (0.1 M), cooled to
0 °C, was treated with MsCl (5.0 equiv) followed by Et3N (5.0
equiv). The reaction mixture was allowed to warm to 25 °C,
stirred for 6 h, diluted with EtOAc, and poured into saturated
aqueous NH4Cl. The aqueous phase was separated and
extracted twice with EtOAc. The organic layers were combined,
dried (Na2SO4), decanted, and concentrated in vacuo.
2-(ter t-Bu tyloxyca r bon yl)-3-flu or o-1,2,9,9a -tetr a h yd r o-
cyclop r op a [c]ben z[e]in d ol-4-on e (5). Flash chromatogra-
phy (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 5 as a
white solid (10.3 mg, 53%): mp 168-170 °C; 1H NMR (250
MHz, C6D6) δ 8.48 (m, 1H), 6.99 (m, 2H), 6.07 (m, 1H), 3.64
(d, J ) 11.0 Hz, 1H), 3.21 (dd, J ) 11.0, 4.6 Hz, 1H), 1.45 (s,
9H), 1.40 (m, 1H), 0.81 (dd, J ) 7.7, 5.1 Hz, 1H), 0.67 (m, 1H);
13C NMR (125 MHz, C6D6) δ 177.2 (d, J ) 17.3 Hz), 151.9,
142.6 (d, J ) 254.3 Hz), 140.1, 138.2 (d, J ) 6.7 Hz), 133.9 (d,
J ) 3.8 Hz), 132.1, 127.8 (d, J ) 2.9 Hz), 127.0, 121.9, 82.8,
53.0, 32.7 (d, J ) 2.9 Hz), 28.3, 26.2, 22.8; 19F NMR (376 MHz,
3-(ter t-Bu tyloxyca r bon yl)-4-ch lor o-1-[[(m eth a n esu lfo-
n yl)oxy]m et h yl]-5-(m et h oxym et h oxy)-1,2-d ih yd r o-3H -
ben z[e]in d ole (29). Flash chromatography (SiO2, 2 × 15 cm,
15% EtOAc-hexanes) afforded 29 as a colorless oil (27 mg,
99%): 1H NMR (250 MHz, CDCl3) δ 8.20 (d, J ) 7.7 Hz, 1H),
7.74 (d, J ) 7.7 Hz, 1H), 7.56 (m, 1H), 7.48 (m, 1H), 5.35 (d, J
) 5.9 Hz, 1H), 5.29 (d, J ) 5.5 Hz, 1H), 4.54 (m, 2H), 4.24-
4.15 (m, 2H), 3.79 (m, 1H), 3.72 (s, 3H), 2.89 (s, 3H), 1.56 (s,
9H); 13C NMR (100 MHz, CDCl3) δ 154.5, 151.7, 140.7, 128.7,
128.1, 127.5, 125.8, 123.8 (2C), 122.9, 117.6, 100.6, 82.3, 68.9,
58.5, 55.7, 41.5, 37.6, 28.1; IR (film) νmax 2978, 1707, 1365, 1332
C6D6) δ -137.3 (s); IR (film) νmax 2979, 1713, 1634, 1371 cm-1
;
UV (THF) λmax 312 (ꢀ ) 25700), 253 (ꢀ ) 14300); nm
MALDIHRMS (DHB) m/z 338.1155 (M+ + Na, C18H18FNO3
requires 338.1163).
cm-1; MALDIHRMS (DHB) m/z 494.1039 (M+ + H, C21H26
-
Natural (-)-5: [R]25 -72 (c 0.28, THF).
D
ClNO7S requires 494.1016).
ent-(+)-5: [R]25 +77 (c 0.20, THF).
D
Natural (-)-(1S)-29: [R]25 -64 (c 1.53, THF).
2-(ter t-Bu t yloxyca r b on yl)-3-ch lor o-1,2,9,9a -t et r a h y-
d r ocyclop r op a [c]ben z[e]in d ol-4-on e (6). Flash chromatog-
raphy (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 6 as
D
ent-(+)-(1R)-29: [R]25 +60 (c 1.35, THF).
D
4-Br om o-3-(ter t-bu tyloxyca r bon yl)-1-[[(m eth a n esu lfo-
n yl)oxy]m et h yl]-5-(m et h oxym et h oxy)-1,2-d ih yd r o-3H -
ben z[e]in d ole (30). Flash chromatography (SiO2, 2 × 15 cm,
15% EtOAc-hexanes) afforded 30 as a colorless oil (34 mg,
95%): 1H NMR (500 MHz, CDCl3) δ 8.21 (d, J ) 8.8 Hz, 1H),
7.74 (d, J ) 8.4 Hz, 1H), 7.56 (m, 1H), 7.48 (m, 1H), 5.33 (d, J
) 5.9 Hz, 1H), 5.27 (d, J ) 5.5 Hz, 1H), 4.53 (d, J ) 10.6 Hz,
2H), 4.54-4.15 (m, 2H), 3.83 (m, 1H), 3.73 (s, 3H), 2.89 (s, 3H),
1.55 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 154.6, 153.2, 142.3,
129.3, 128.3, 127.7, 125.9, 124.2, 124.1, 123.1, 107.7, 100.9,
82.4, 68.8, 58.6, 55.8, 41.9, 37.7, 28.3; IR (film) νmax 2976, 1707,
1
a white solid (10.5 mg, 77%): mp 152-154 °C; H NMR (500
MHz, C6D6) δ 8.46 (m, 1H), 7.01 (m, 2H), 6.99 (m, 1H), 3.76
(d, J ) 11.0 Hz, 1H), 3.20 (dd, J ) 11.0, 4.0 Hz, 1H), 1.43 (s,
9H), 1.41 (m, 1H), 0.89 (dd, J ) 7.3, 5.1 Hz, 1H), 0.76 (m,
1H);13C NMR (125 MHz, C6D6) δ 179.6, 153.4, 152.0, 140.1,
133.2, 132.2, 128.3, 127.1, 121.9, 118.9, 82.9, 53.1, 34.3, 28.4,
26.3, 23.1; IR (film) νmax 2978, 1713, 1623, 1368 cm -1; UV
(THF) λmax 307 (ꢀ ) 20000), 251 (ꢀ ) 10300) nm; FABHRMS
(NBA/NaI) m/z 332.1045 (M++ H, C18H18ClNO3 requires
332.1053).
1360, 1331 cm-1; MALDIHRMS (DHB) m/z 538.0528 (M+
+
Natural (+)-6: [R]25 +33 (c 0.32, THF).
D
Na, C21H26BrNO7S requires 538.0506).
ent-(-)-6: [R]25 -35 (c 0.53, THF).
D
Natural (-)-(1S)-30: [R]25 -38 (c 1.41, THF).
3-Br om o-2-(ter t-b u t yloxyca r b on yl)-1,2,9,9a -t et r a h y-
d r ocyclop r op a [c]ben z[e]in d ol-4-on e (7). Flash chromatog-
raphy (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 7 as
a white solid (28 mg, 46%): mp 140-142 °C; 1H NMR (250
MHz, C6D6) δ 8.45 (m, 1H), 6.99 (m, 2H), 6.08 (m, 1H), 3.78
(d, J ) 10.9 Hz, 1H), 3.18 (dd, J ) 10.9, 4.4 Hz, 1H), 1.40 (s,
9H), 1.39 (m, 1H), 0.90 (dd, J ) 7.3, 5.1 Hz, 1H), 0.79 (m, 1H);
13C NMR (100 MHz, C6D6) δ 179.8, 156.4, 151.8, 140.3, 132.7,
132.2, 128.3, 127.1, 121.9, 111.3, 82.9, 53.1, 35.1, 28.4, 26.2,
23.2; IR (film) νmax 2960, 1715, 1619, 1368 cm-1; UV (THF)
D
ent-(+)-(1R)-30: [R]25 +39 (c 1.29, THF).
D
3-(ter t-Bu tyloxyca r bon yl)-4-iod o-1-[[(m eth a n esu lfon y-
l)oxy]m eth yl]-5-(m eth oxym eth oxy)-1,2-d ih yd r o-3H-ben z-
[e]in d ole (31). Flash chromatography (SiO2, 2 × 15 cm, 15%
EtOAc-hexanes) afforded 31 as a colorless oil (46 mg, 94%):
1H NMR (250 MHz, CDCl3) δ 8.21 (d, J ) 8.4 Hz, 1H), 7.74 (d,
J ) 8.0 Hz, 1H), 7.57 (m, 1H), 7.46 (m, 1H), 5.32 (d, J ) 5.5
Hz, 1H), 5.24 (d, J ) 5.5 Hz, 1H), 4.53 (m, 2H), 4.18 (m, 2H),
3.86 (m, 1H), 3.75 (s, 3H), 2.88 (s, 3H), 1.57 (s, 9H); 13C NMR
(125 MHz, CDCl3) δ 156.7, 154.6, 145.4, 130.2, 128.5, 127.0,
125.8, 124.3, 123.9, 123.0, 101.4, 83.4, 82.5, 68.8, 58.7, 55.7,
λ
max 311 (ꢀ ) 21400), 255 (ꢀ ) 17300) nm; MALDIHRMS (DHB)
m/z 296.1300 ((M - Br)+, C18H18NO3 requires 296.1289);
ESIMS m/z 376 (M+ + H, C18H18BrNO3 requires 376).
42.2, 37.7, 28.4; IR (film) νmax 2979, 1709, 1359, 1331 cm-1
;
FABHRMS (NBA/CsI) m/z 695.9542 (M+ + Cs, C21H26INO7S
Natural (+)-7: [R]25 +42 (c 0.11, THF).
D
requires 695.9529).
ent-(-)-7: [R]25 -40 (c 0.09, THF).
D
Natural (+)-(1S)-31: [R]25 +19 (c 0.54, THF).
2-(ter t-Bu t yloxyca r bon yl)-3-iod o-1,2,9,9a -t et r a h yd r o-
cyclop r op a [c]ben z[e]in d ol-4-on e (8). Flash chromatogra-
phy (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 8 as a
white solid (4.8 mg, 61%): mp 145 °C dec; 1H NMR (250 MHz,
C6D6) δ 8.46 (m, 1H), 6.97 (m, 2H), 6.06 (m, 1H), 3.82 (d, J )
11.3 Hz, 1H), 3.15 (dd, J ) 10.9, 4.0 Hz, 1H), 1.46 (s, 9H),
1.39 (m, 1H), 0.90 (m, 1H), 0.81 (m, 1H); 13C NMR (125 MHz,
C6D6) δ 181.3, 161.6, 151.5, 140.7, 132.2, 131.4, 128.8, 127.1,
121.8, 92.3, 82.9, 52.7, 35.5, 28.6, 26.1, 23.4; IR (film) νmax 2979,
1715, 1601, 1367 cm-1; UV (THF) λmax 319 (ꢀ ) 21300), 248 (ꢀ
) 14900 nm); MALDIHRMS (DHB) m/z 446.0229 (M+ + Na,
C18H18INO3 requires 446.0229). Recrystallization from EtOAc-
hexanes provided colorless plates suitable for X-ray structure
determination.24
D
ent-(-)-(1R)-31: [R]25 -18 (c 0.49, THF).
D
3-(ter t-Bu tyloxyca r bon yl)-1-[[(m eth a n esu lfon yl)oxy]-
m eth yl]-5-(m eth oxym eth oxy)-4-m eth yl-1,2-d ih yd r o-3H-
ben z[e]in d ole (32). Flash chromatography (SiO2, 2 × 15 cm,
15% EtOAc-hexanes) afforded 32 as a colorless oil (9.5 mg,
88%): 1H NMR (500 MHz, CDCl3) δ 8.13 (d, J ) 8.1 Hz, 1H),
7.41 (d, J ) 8.4 Hz, 1H), 7.48 (m, 1H), 7.42 (m, 1H), 5.22 (d, J
) 5.9 Hz, 1H), 5.14 (d, J ) 5.9 Hz, 1H), 4.53 (m, 2H), 4.19-
4.12 (m, 2H), 3.78 (m, 1H), 3.68 (s, 3H), 2.85 (s, 3H), 2.39 (s,
3H), 1.55 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 155.1, 153.7,
143.4, 128.9, 127.2, 126.9, 125.2, 123.7, 123.0, 121.8, 121.6,
100.6, 81.9, 69.6, 58.3, 55.5, 41.3, 37.9, 28.6, 15.1; IR (film)
νmax 2977, 1704, 1360, 1334 cm-1; FABHRMS (NBA/CsI) m/z
584.0706 (M+ + Cs, C22H29NO7S requires 584.0719).
Natural (+)-8: [R]25 +155 (c 0.24, THF).
D
Natural (-)-(1S)-32: [R]25 -72 (c 0.45, THF).
ent-(-)-8: [R]25 -145 (c 0.29, THF).
D
D
ent-(+)-(1R)-32: [R]25 +72 (c 0.48, THF).
2-(ter t-Bu t yloxyca r b on yl)-3-m et h yl-1,2,9,9a -t et r a h y-
d r ocyclop r op a [c]ben z[e]in d ol-4-on e (9). Flash chromatog-
raphy (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 9 as
D
Selective MOM Eth er Dep r otection of Ben zen e-
su lfon a te 28 a n d Mesyla tes 29-32 w ith Su bsequ en t in
Situ Sp ir ocycliza tion . Gen er a l P r oced u r e. A solution of
the sulfonate in i-PrOH-THF (0.02 M, 1:1) was treated with
concentrated HCl (75 equiv) and stirred for 4 h at 25 °C. The
1
a white solid (4.7 mg, 76%): mp 183-185 °C; H NMR (500
MHz, C6D6) δ 8.61 (m, 1H), 7.07 (m, 2H), 6.23 (m, 1H), 3.88
(d, J ) 11.0 Hz, 1H), 3.21 (dd, J ) 10.8, 4.2 Hz, 1H), 2.28 (s,

5172 J . Org. Chem., Vol. 66, No. 15, 2001
Boger et al.
3H), 1.49 (m, 1H), 1.33 (s, 9H), 0.95 (dd, J ) 7.3, 5.1 Hz, 1H),
0.78 (m, 1H); 13C NMR (125 MHz, C6D6) δ 186.1, 153.0, 152.9,
141.2, 133.8, 131.7, 127.9, 126.8, 122.8, 121.9, 81.8, 52.5, 31.9,
28.4, 25.4, 22.7, 14.6; IR (film) νmax 2979, 1713, 1630, 1365
cm-1; UV (THF) 301 (ꢀ ) 16000), 254 (ꢀ ) 9200) nm FABHRMS
(NBA/NaI) m/z 312.1611 (M+ + H, C19H21NO3 requires
312.1600).
Natural (+)-9: [R]25 +63 (c 0.24, THF).
D
ent-(-)-9: [R]25 -60 (c 0.24, THF).
D
P r ep a r a tion of N-CO2Me Der iva tives 33-36 for Sin gle-
Cr ysta l X-r a y An a lysis. Gen er a l P r oced u r e. The sulfonate
(28-32) was treated with 4 N HCl-EtOAc (0.5 mL) and stirred
for 30 min at 25 °C. The solvent was removed under a stream
of N2 and the residual salt was placed under vacuum. This
salt was suspended in THF (1.0 mL) and treated with NaHCO3
(2.2 equiv) and ClCO2CH3 (3.0 equiv), and the mixture was
stirred for 3 h. Aqueous 10% NaHCO3 was added to the
reaction mixture, and stirring was continued for 1 h. The
reaction mixture was diluted with EtOAc, and the aqueous
phase separated and extracted twice with EtOAc. The organic
layers were combined, dried (Na2SO4), decanted, and concen-
trated in vacuo.
3-F lu or o-2-(m eth oxyca r bon yl)-1,2,9,9a -tetr a h yd r ocy-
clop r op a [c]ben z[e]in d ol-4-on e (33). Flash chromatography
(SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 33 as a
white solid (15 mg, 82%): mp 171-173 °C; 1H NMR (400 MHz,
C6D6) δ 8.46 (m, 1H), 6.99 (m, 2H), 6.08 (m, 1H), 3.57 (d, J )
10.6 Hz, 1H), 3.43 (s, 3H), 3.18 (dd, J ) 11.1, 4.4 Hz, 1H),
1.43 (m, 1H), 0.79 (dd, J ) 7.5, 4.9 Hz, 1H), 0.59 (m, 1H); IR
(film) νmax 2922, 1723, 1634, 1294 cm-1. The identity of 33 was
confirmed with a single-crystal X-ray structure obtained from
a colorless, cubic crystal grown from EtOAc-hexanes.24
3-Ch lor o-2-(m eth oxyca r bon yl)-1,2,9,9a -tetr a h yd r ocy-
clop r op a [c]ben z[e]in d ol-4-on e (34). Flash chromatography
(SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 34 as a
white solid (9.2 mg, 70%): mp 165-167 °C; 1H NMR (400 MHz,
C6D6) δ 8.48 (m, 1H), 6.98 (m, 2H), 6.04 (m, 1H), 3.59 (d, J )
10.9 Hz, 1H), 3.44 (s, 3H), 3.16 (dd, J ) 10.9, 4.4 Hz, 1H),
1.34 (m, 1H), 0.80 (m, 1H), 0.62 (m, 1H); IR (film) νmax 2954,
1723, 1622, 1374 cm-1. The identity of 34 was confirmed with
a single-crystal X-ray structure obtained from a colorless,
parallelpipe-shaped crystal grown from EtOAc-hexanes.24
3-Br om o-2-(m et h oxyca r bon yl)-1,2,9,9a -t et r a h yd r ocy-
clop r op a [c]ben z[e]in d ol-4-on e (35). Flash chromatography
(SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 35 as a
white solid (6.5 mg, 68%): mp 142-144 °C; 1H NMR (400 MHz,
C6D6) δ 8.47 (m, 1H), 6.97 (m, 2H), 6.04 (m, 1H), 3.62 (d, J )
10.6 Hz, 1H), 3.46 (s, 3H), 3.16 (dd, J ) 11.1, 4.4 Hz, 1H),
1.34 (m, 1H), 0.81 (dd, J ) 7.5, 4.9 Hz, 1H), 0.65 (m, 1H); IR
(film) νmax 2954, 1721, 1617, 1439 cm-1. The identity of 35 was
confirmed with a single-crystal X-ray structure obtained from
a colorless, parallelpipe-shaped crystal grown from EtOAc-
hexanes.24
2-(Meth oxyca r bon yl)-3-m eth yl-1,2,9,9a -tetr a h yd r ocy-
clop r op a [c]ben z[e]in d ol-4-on e (36). Flash chromatography
(SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded 36 as a
white solid (8.0 mg, 80%): mp 189-191 °C; 1H NMR (500 MHz,
C6D6) δ 8.59 (m, 1H), 7.07 (m, 2H), 6.22 (m, 1H), 3.76 (d, J )
11.0 Hz, 1H), 3.34 (s, 3H), 3.19 (dd, J ) 10.9, 4.4 Hz, 1H),
2.20 (s, 3H), 1.46 (m, 1H), 0.89 (dd, J ) 7.1, 4.9 Hz, 1H), 0.67
(m, 1H); IR (film) νmax 2955, 1716, 1628, 1366 cm-1. The
identity of 36 was confirmed with a single-crystal X-ray
structure obtained from a colorless, parallelpipe-shaped crystal
grown from Et2O-cyclohexane.24
Resolu tion . A solution of racemic intermediate (21, 24-
27; 15 mg per injection) in 50% i-PrOH-hexanes (200 µL) was
resolved on a semipreparative Daicel Chiralcel OD column (10
µm, 2 × 25 cm) using 7% i-PrOH-hexanes as eluent (12 mL/
min). The effluent was monitored at 254 nm, and the enan-
tiomers were eluted with retention times as follows: (+)-21
(20.1 min), (-)-21 (22.5 min), R ) 1.15; (+)-24 (25.8 min), (-)-
24 (39.3 min), R ) 1.46; (+)-25 (27.7 min), (-)-25 (46.3 min),
R ) 1.66; (+)-26 (28.5 min), (-)-26 (55.3 min), R ) 1.98; (+)-
27 (17.5 min), (-)-27 (31.5 min), R ) 1.80. (-)-21 was
reinjected in order to obtain > 99% ee material, unlike all
F igu r e 8. HPLC analysis (Chiralcel AD, 10% i-PrOH in
hexanes) of the acid-catalyzed addition of methanol to (a) (-)-7
and (b) (()-7.
others which were found to be >99% enantiomerically pure
after a single injection.
Aqu eou s Solvolysis of 5-9. A sample of 5-9 (75 µg) was
dissolved in CH3OH (1.5 mL), and the resultant solution was
mixed with universal aqueous buffer (pH 2-10, 1.5 mL,
B(OH)3-citric acid-Na3PO4). The UV spectrum of the solution
was measured immediately after mixing then approximately
every 24 h until no further change in the spectrum was
observed. The decrease in absorbance for 5-9 was measured
at 318, 318, 318, 324 and 313 nm, respectively, while the
increase in absorbance was measured at 247, 249, 248, 251
and 247 nm. The solvolysis rate was calculated as the slope of
the plot ln[(Af - Ai)/(Af - A)] versus time (Table 1).
Acid -Ca t a lyzed Ad d it ion of CH 3OH t o 5-9. Gen er a l
P r oced u r e. A solution of the C3-substituted N-Boc-CBI (5-
9, 1.0 equiv) in CH3OH (0.01 M) was treated with CF3SO3H
(0.12 equiv, 0.01 M solution in CH3OH) at 0 °C. The reaction
mixture was allowed to slowly warm to 25 °C over 24 h and
then quenched with the addition of NaHCO3 (5 mg). The
reaction was decanted, and the crude material was absorbed
onto a minimal amount of SiO2 then loaded directly onto a
prepacked flash column and eluted to afford the solvolysis
product(s).
HPLC resolution of the addition reactions to (()- and (+)-
5-9 established the ratio of reaction regioselectivity (see
Scheme 5) and the exclusive SN2 mechanism of addition by
affording a single enantiomer of 41-46. A representative
example of such analysis for 7 is shown in Figure 8. The chiral
phase HPLC traces of the remainder may be found in the
Supporting Information (Figures 9-12).
4-(ter t-Bu tyloxyca r bon yl)-5-flu or o-6-h yd r oxy-2-m eth -
oxy-1,2,3,4-tetr a h yd r oben zo[f]qu in olin e (41) a n d 3-(ter t-
Bu tyloxyca r bon yl)-4-flu or o-5-h yd r oxy-1-(m eth oxym eth -
yl)-1,2-dih ydr o-3H-ben z[e]in dole (42). Flash chromatography
(SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded a 1:4
mixture of 41 and 42 (10.3 mg, 82%) that required additional
separation using a semipreparative Daicel Chiralcel OD
column (10 µm, 2 × 25 cm) with 7% i-PrOH-hexanes as eluent
(12 mL/min) to afford each pure. For 41: 1H NMR (500 MHz,
C6D6) δ 8.34 (d, J ) 8.4 Hz, 1H), 7.44 (d, J ) 8.4 Hz, 1H), 7.22
(m, 2H), 5.29 (br s, 1H), 4.61 (br m, 1H), 3.22 (br m, 5H), 2.81
(br s, 2H), 1.46 (s, 9H); IR (film) νmax 3347, 2929, 1703, 1460

C3-Substituted CBI Analogues of CC-1065 and the Duocarmycins
cm-1; MALDIHRMS (DHB) m/z 370.1425 (M+ + Na, C19H22
FNO4 requires 370.1410). The identity of 41 was confirmed
with a single-crystal X-ray structure obtained from a colorless,
cubic crystal grown from EtOAc-hexanes.24
J . Org. Chem., Vol. 66, No. 15, 2001 5173
-
tography (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded
45 as a white foam (5.7 mg, 85%): 1H NMR (400 MHz, C6D6)
δ 8.44 (m, 1H), 7.46 (m, 1H), 7.23 (m, 2H), 5.84 (s, 1H), 4.97-
3.85 (m, 2H), 3.28-2.44 (m, 6H), 1.39 (s, 9H); IR (film) νmax
3402, 2928, 1704, 1450 cm-1; MALDIHRMS (DHB) m/z
328.1538 ((M-I)+, C19H22NO4 requires 328.1543); ESIMS m/z
454 ((M - H)-, C18H22NO4 requires 454).
For 42: 1H NMR (400 MHz, C6D6) δ 8.34 (d, J ) 7.6 Hz,
1H), 7.41 (d, J ) 8.8 Hz, 1H), 7.20 (m, 2H), 5.92 (s, 1H), 4.56
(d, J ) 11.2 Hz, 1H), 3.78 (m, 1H), 3.34 (m, 1H), 3.11 (m, 2H),
2.97 (s, 3H), 1.49 (s, 9H); IR (film) νmax 3401, 2978, 1711, 1366
4-(ter t-Bu tyloxycar bon yl)-6-h ydr oxy-2-m eth oxy-5-m eth -
yl-1,2,3,4-tetr a h yd r oben zo[f]qu in olin e (46). Flash chro-
matography (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded
46 as a white foam (2.8 mg, 82%): 1H NMR (500 MHz, C6D6)
δ 8.22 (m, 1H), 7.60 (m, 1H), 7.27 (m, 2H), 4.84 (d, J ) 13.3
Hz, 1H), 4.63 (s, 1H), 3.33 (s, 3H), 3.18-2.57 (m, 4H), 2.07 (s,
cm-1; MALDIHRMS (DHB) m/z 370.1425 (M+ + Na, C19H22
-
FNO4 requires 370.1425).
4-(ter t-Bu tyloxyca r bon yl)-5-ch lor o-6-h yd r oxy-2-m eth -
oxy-1,2,3,4-tetr a h yd r oben zo[f]qu in olin e (43). Flash chro-
matography (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded
1
43 as a white solid (6.8 mg, 86%): mp 127-129 °C; H NMR
3H), 1.32 (s, 9H); IR (film) νmax 3418, 2929, 1673, 1367 cm-1
;
(400 MHz, C6D6) δ 8.46 (m, 1H), 7.46 (m, 1H), 7.28 (m, 2H),
5.91 (s, 1H), 4.80 (m, 1H), 3.34-2.52 (m, 7H), 1.44 (s, 9H); IR
(film) νmax 3384, 2925, 1704, 1585 cm-1; MALDIHRMS (DHB)
m/z 364.1301 (M+ + H, C19H22ClNO4 requires 364.1310). The
identity of 43 was confirmed with a single-crystal X-ray
structure obtained from a colorless, cubic crystal grown from
EtOAc-hexanes.24
MALDIHRMS (DHB) m/z 343.1775 (M+, C20H25NO4 requires
343.1778).
Ack n ow led gm en t. We gratefully acknowledge the
financial support of the National Institutes of Health
(CA41986), the Skaggs Institute for Chemical Biology,
and Corixa Pharmaceuticals. We thank the American
Cancer Society for a postdoctoral fellowship (S.R.B.,
1999-2001), Dr. Raj K. Chadha for the X-ray structure
determinations, and Michael P. Hedrick for conducting
the cytotoxicity studies.
5-Br om o-4-(ter t-bu tyloxyca r bon yl)-6-h yd r oxy-2-m eth -
oxy-1,2,3,4-tetr a h yd r oben zo[f]qu in olin e (44). Flash chro-
matography (SiO2, 1.5 × 15 cm, 25% EtOAc-hexanes) afforded
1
44 as a white solid (2.8 mg, 89%): mp 123-125 °C; H NMR
(600 MHz, C6D6) δ 8.38 (m, 1H), 7.48 (m, 1H), 7.24 (m, 2H),
5.89 (s, 1H), 4.75 (m, 1H), 3.79 (m, 1H), 3.28-2.55 (m, 6H),
1.39 (s, 9H); IR (film) νmax 3381, 2930, 1703, 1583, 1368 cm-1
;
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
5-9, 18-22, 24-36, and 41-46 and copies of the chiral-phase
HPLC traces of the acid-catalyzed CH3OH addition products
to 5-9. This material is available free of charge via the
Internet at http://pubs.acs.org.
MALDIHRMS (DHB) m/z 430.0628 (M+ + Na, C19H22BrNO4
requires 430.0624). The identity of 44 was confirmed with a
single-crystal X-ray structure obtained from a colorless, cubic
crystal grown from EtOAc-hexanes.24
4-(ter t-Bu tyloxycar bon yl)-6-h ydr oxy-5-iodo-2-m eth oxy-
1,2,3,4-tetr a h yd r oben zo[f]qu in olin e (45). Flash chroma-
J O010309G