Discovery of a fluoroindolo[2,3-a]carbazole clinical candidate with broad spectrum antitumor activity in preclinical tumor models superior to the marketed oncology drug, CPT-11

Article abstract of DOI:10.1021/jm049090z

A series of fluoroglycosylated fluoroindolocarbazoles was examined with respect to their topoisomerase I activity, cytotoxicity, and selectivity. The lead clinical candidate from this series, BMS-250749, displays broad spectrum antitumor activity superior

Full text of DOI:10.1021/jm049090z

2258
J. Med. Chem. 2005, 48, 2258-2261
Letters
Discovery of a
Fluoroindolo[2,3-a]carbazole Clinical
Candidate with Broad Spectrum
Antitumor Activity in Preclinical Tumor
Models Superior to the Marketed
Oncology Drug, CPT-11†
Mark G. Saulnier,* Balu N. Balasubramanian,*
Byron H. Long, David B. Frennesson,
Edward Ruediger, Kurt Zimmermann,
The discovery of 1 stems from a program directed
toward the design of topo I selective agents in a novel
class of glycosylated indolo[2,3-a]carbazoles and benz-
thiopheno[2,3-a]carbazoles, wherein both the core and
sugar moieties are modified with fluorine substituents.
Jeffrey T. Eummer, Denis R. St. Laurent,
Karen M. Stoffan, B. Narasimhulu Naidu,
Mikael Mahler, Francis Beaulieu, Carol Bachand,
Frank Y. Lee, Craig R. Fairchild, Linda K. Stadnick,
William C. Rose, Carola Solomon, Henry Wong,
Alain Martel, John J. Wright, Robert Kramer,
David R. Langley, and Dolatrai M. Vyas
The rationale for introduction of fluoroglycosides is
based on the hypothesis that substitution of fluorine for
sugar hydroxyl may serve to remove potential sites of
metabolic liability while concomitantly modulating li-
pophilicity, one of the parameters influential in impart-
ing in vivo distal site activity. It is also apparent that
such fluorine substitution would maintain hydrogen
bond accepting potential in the DNA/topo I/analogue
ternary complex. Several of these novel analogues
reported herein, including 1, 2, and 3, display greatly
enhanced topo I and cytotoxic potencies vis-a`-vis the
parent glucosyl analogues. In addition, it is noteworthy
that 3 exhibits highly specific topo I mediated cytotox-
icity similar to camptothecin (CPT).7
The synthesis of the indolocarbazole core8 and its
glycosylation9 are well described in the literature.6,10
The synthetic routes to the analogues described in Table
1 are delineated in Schemes 1 and 2, using the examples
pertaining to the 3,9-difluoroindolocarbazole core. In-
troduction of fluorine into the 2′, 4′, and 6′-positions of
the sugar portion of the molecule is accomplished both
pre and post glycosylation. To illustrate, 6′-fluoro-2′,3′,4′-
tri-(O)-benzyl-D-glucopyranose11 (4) is prepared from the
known12 6′-fluoro-1′,2′,3′,4′-tetra-(O)-acetyl-R-D-glucopy-
ranose and then coupled with the N-6-(4-tert-butyl)-
benzyl-3,9-difluoroindolo[2,3-a]carbazole core 5,13 using
the Mitsunobu protocol.14 Further processing by transfer
hydrogenolysis followed by deprotection of the N-6-(4-
tert-butyl)benzyl group15 provides the desired 6′-fluoro
analogue 6 (Scheme 1).
In fashion similar to the method described above, 2′-
fluoro-3′,4′,6′-tri-(O)-benzyl-D-glucopyranose16 and 4′-
fluoro-2′,3′,6′-tri-(O)-benzyl-D-glucopyranose are con-
verted into their respective 2′-fluoro and 4′-fluoro (1)
analogues.17
The optimal procedure for the synthesis of 4′-fluoro-
glycoside analogues involves post-glycosylative modifi-
cation of a D-galactofluoroindolocarbazole intermediate
7 as shown in Scheme 2. Thus, conversion of the 4′-axial
hydroxyl in 7 to an equatorial 4′-fluorine proceeds in
reasonable yield, and with complete inversion of con-
figuration, using 4-DMAP-attenuated DAST. Base-
The Bristol-Myers Squibb Pharmaceutical
Research Institute, 5 Research Parkway,
Wallingford, Connecticut 06492, The Bristol-Myers Squibb
Pharmaceutical Research Institute, P.O. Box 4000,
Princeton, New Jersey 08543, and The Bristol-Myers Squibb
Pharmaceutical Research Institute, Candiac,
QC, Canada J5R 1J1
Received November 10, 2004
Abstract: A series of fluoroglycosylated fluoroindolocarbazoles
was examined with respect to their topoisomerase I activity,
cytotoxicity, and selectivity. The lead clinical candidate from
this series, BMS-250749, displays broad spectrum antitumor
activity superior to CPT-11 against some preclinical xenograft
models, including curative antitumor activity against Lewis
lung carcinoma.
The glycosylated indolo[2,3-a]carbazole pharmacoph-
ore is a rich structural motif that is encompassed in
many anticancer agents and kinase inhibitors including
UCN-01.1-4 In this context, we and others have discov-
ered that this class of compounds also exhibits topoi-
somerase I (topo I) inhibition4-6 and DNA cleaving
activity.
Introduction of 3,9-difluoro substitution into the in-
dolocarbazole confers topo I selectivity within this series
of analogues.6-7 From our initial investigations, it
became apparent to us that the plasma, tumor levels,
physiochemical properties, and overall metabolism and
pharmacokinetic (M-PK) properties of the analogues
play a significant role in imparting distal site antitumor
activity in animal models.6 In this letter, we disclose
the discovery of BMS-250749 (1), a fluoroglycosyl-3,9-
difluoroindolocarbazole topo I inhibitor which, by virtue
of its robust in vitro and in vivo preclinical profile
reported herein, has entered human clinical trials.
† Dedicated to the memory of Dr. Monroe Wall, who made significant
contributions to the field of natural product-based cytotoxic agents.
* To whom correspondence should be addressed. M.G.S.: tel, 203-
677-6325; fax, 203-677-7702; email, Mark.Saulnier@bms.com. B.N.B.:
tel, 203-677-6693; fax, 203-677-7884; email, balu@bms.com.
10.1021/jm049090z CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/16/2005

Letters
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 7 2259
Table 1. Topo I Potency and Cytotoxicity of Fluorosugar
Analogues
Scheme 2. Synthesis of 4′-Fluoro (1), 4′,6′-Difluoro (2),
and 4′,4′-gem-Difluoro (8) Analoguesa
compd
core
X
W
Y
Z
Topoa P388b
R/Sc
183
98
110
110
119
52
13
6
10
11
12
17
1
18
3
14
2
8
3,9-diF
3,9-diF
3,9-diF
3,9-diF
Tetra-Fd
NH OH
H
OH 0.24 0.018
OH 0.48 0.050
H
OH 0.42 0.016
OH 1.50 0.052
OH 3.00 0.034
F
F
F
F
F
F
F
F
F
NH
NH
S
F
F
F
F
F
H
OH
H
H
H
H
H
H
H
H
F
4.4
0.012
S
a Reagents and conditions: (a) Ph3P, DIAD, THF. (b) 20%
Pd(OH)2/C, cyclohexene, EtOH, reflux. (c) PhCOCl, Pyr, -5 °C,
20 min. (d) DAST, 4-DMAP, -50 to 45 °C. (e) 4.45 M KOH, EtOH,
5 to 25 °C, 24 h. (f) concd HCl. (g) NH4OAc, EtOH, reflux 48 h. (h)
4.45 M KOH, EtOH, 5 °C, 20 min. (i) Dess-Martin periodinane
([1,1,1-tris(acetyloxy)-1,1-dihydro-1,2-benziodoxol-3-(1H)-one).
Tetra-F NH
3,9-diF
2,10-diF NH OH
Tetra-F OH
Tetra-F NH OH
NH OH
0.11 0.002
0.20 0.003
380
59
S
0.04 0.003e >1658
0.75 0.004
0.41 0.004
0.08 0.003
0.50 0.0004
0.05 0.060
0.07 0.014
500
450
380
580
16
3,9-diF
3,9-diF
Tetra-F
Tetra-F NH NH2
3,9-diF NH NH2
NH
NH OH
OH
F
15
16
9
S
F
herein employs covalently closed, supercoiled phage
PM2 DNA as the substrate and was previously de-
scribed.6 The topo I selectivity of these analogues is
determined as previously reported6 using P388 cells
which express high levels of topo I (and are therefore
sensitive to topo I targeting agents such as CPT) and a
camptothecin resistant cell line (P388/CPT45) derived
from the parental line that expresses little or no
topoisomerase I. This cell line overexpresses topoi-
somerase II, which serves to compensate for the lack of
topoisomerase I, and is thus resistant to topo I active
agents such as CPT. Cells that do not express detectable
levels of topo I are completely resistant to camptothecin
and its analogues.6 Thus, camptothecin treatment re-
sults in a very high R/S ratio and an agent that is
cytotoxic by a non-topoisomerase I mechanism would
kill both lines equally and result in an R/S ratio near
1.0. A ratio (R/S) of the IC50 values for P388/CPT45
versus P388 cells for an analogue is an indication of topo
I selectivity expressed by the analogue. The cytotoxic
effects of topo I active agents are directly proportional
to the number of DNA breaks they form. Therefore, cells
that express high levels of topo I are sensitive to these
agents, and conversely, cells that express low levels of
the enzyme are more resistant to these agents. Topo I
levels are generally higher in cancer cells than in
normal cells, a feature that is most likely a reflection
of higher proliferation rates in transformed cells. The
topo I activity (for DNA breaks), P388 cell cytotoxic
potency, and R/S ratio of each these novel fluoroglyco-
sylated fluoroindolo[2,3-a]carbazoles and fluoroglycosy-
lated fluorobenzthiopheno[2,3-a]carbazoles are reported
in Table 1.
F
H
37
a Ratio of the median effective concentration (EC50, µM)) of drug
for inducing single-strand breaks in the DNA substrate divided
by that obtained for CPT in the same experiment. CPT has a mean
Topo I EC50 ) 160 nM. b Mean cytotoxic concentration (IC50, µM)
following 3 days of continuous exposure of P388 murine leukemia
cells to drug. CPT has a mean P388 IC50 ) 36 nM. c Ratio of the
IC50 value obtained for P388/CPT45 cells (cells that have acquired
high levels of CPT resistance) divided by that obtained for parental
P388 cells. d Tetra-F is 2,3,9,10-tetrafluoro. e <0.003.
Scheme 1. Synthesis of 6′-Fluoro Analogue 6a
a Reagents and conditions: (a) Ph3P, DIAD, THF. (b) 20%
Pd(OH)2/C, cyclohexene, EtOH, reflux. (c) 4.45 M KOH, EtOH, rt,
24 h. (d) concd HCl. (e) NH4OAc, EtOH reflux 48 h.
induced global deblocking of the resulting 4′-fluoro-
2′,3′,6′-tribenzoate provides 1. Tribenzoate 7 is also a
key intermediate for the synthesis of the 4′,6′-difluoro
analogue 2 and the 4′,4′-gem-difluoro analogue 8. Both
4′-fluoro and 4′,4′-gem-difluoro analogues are suitable
substrates for direct conversion of their free 6′-hydroxyl
groups to 6′-amino, via reduction of their initially
derived 6′-azides.6 Thus, the 4′-fluoro-6′-amino analogue
9 is easily obtained from 1.
Inspection of Table 1 reveals some interesting SAR
trends regarding the position of fluorine substitution17
on the glycosyl moiety and its effect on topo I selectivity.
In general, substitution of the 6′-OH by 6′-F (as in 6,
10, 11, 12) results in the loss of topo I selectivity vis-
a`-vis their corresponding parent glucose analogues10
(e.g. 13). In contrast, 4′-fluorine (equatorial) substitution
of C-4′-OH (e.g. 1, 3, 14) has the opposite effect: It
enhances the topo I selectivity, thus demonstrating the
Our assay for determining the extent of topo I
mediated DNA cleavage for the analogues described

2260 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 7
Letters
Table 2. Antitumor Efficacy of Lead Analogues vs CPT-11 in
HT29 Xenograft Model
optimal effect in LCK optimal dose (MTD) schedule,b
drug
(cures/total)
(mg/kg/inj)
route
1
2
3
3.1 (2/8)
1.6 (0/8)
>2.3 (2/8)
1.9 (0/8)
20 (30)a
q2dx5, iv
q2dx5, iv
2q2dx5, iv
q2dx5, iv
13a
11a
CPT-11
50a
a MTD likely reached. MTD may be distinct from optimal dose,
in which case MTD is shown in parentheses. b q2dx5; once a day
iv dosing administered every other day for five doses: 2q2dx5;
twice a day iv dosing administered every other day for five doses.
importance of such fluorine for hydroxyl substitution in
the sugar moiety. Substitution of the 2′-hydroxyl for
fluorine slightly improves topo I potency, but poor cell
permeability of this analogue may account for its weak
cytotoxicity.17 The selectivity ratio for 3 is similar to
camptothecin and is the highest we have observed to
date for an indolocarbazole analogue. Bis-substitution
of C-4′ and C-6′ for fluorine, as in 2, substantially
increases the topo I selectivity vis-a`-vis the parent gluco
analogue 13.
Enhancements in P388 cytotoxic potency relative to
their corresponding glucose counterparts are also real-
ized with fluorinated glycosyl analogues, e.g. the C-4′
geminal difluoro analogues 8 and 15. The combination
of 4′,4′-gem-difluoro substitution with the tetrafluo-
robenzothiopheno[2,3-a]carbazole chromophore (15) leads
to the most cytotoxic (0.4 nM vs P388), yet still highly
topo I specific analogue. The two C-6′-NH2 analogues
16 and 9 display enhanced fluorine-mediated topo I
potency vis-a`-vis parent 13, yet their significantly lower
topo I selectivity suggests that additional mechanisms
might be involved.
Our initial premise to introduce fluorine into the
glycosyl moiety of 13 for imparting distal antitumor
activity proved to be correct. As a case in point, it is
noteworthy that 6′-fluoro analogue 6 provides signifi-
cantly increased exposure levels relative to the parent
analogue 136 (plasma levels >100 fold above the IC50
following iv administration at 24 mg/kg/inj) and also
displays in vivo distal site antitumor activity (LCK )
1.2, 21 mg/kg/inj, the MTD in 10:10:80, cremophor:
ethanol:water formulation) comparable to CPT-11 against
the A2780 xenograft model.
On the basis of the topo I selectivity and cytotoxic
potency, as well as the in vivo plasma and tumor
concentrations at 6 h after iv administration in tumor
bearing mice,6 a number of analogues were profiled for
their antitumor activity in the A2780 human ovarian
carcinoma xenograft model as a primary screen. In
particular, the mean 6 h plasma concentrations in nude
mice (A2780 xenograft model) for the three analogues
3 (12 mg/kg), 1 (24 mg/kg), and 2 (8 mg/kg) are 40, 33,
and 27-fold greater than their A2780 cellular IC50
values. In fact, all three compounds show in vivo efficacy
comparable to CPT-11 in A2780. Thus, the three ana-
logues were identified as leading candidates for ad-
vanced in vivo evaluation against a panel of human
tumor xenograft animal models.
Figure 1. Antitumor activity of 1 vs Lewis lung carcinoma.
CPT-11 is about as active as 1 at 13 mg in this model.
that all three fluorosugar analogues show efficacy equal
to or better than CPT-11 in this animal model.
Single dose pharmacokinetics of 1 in mice was deter-
mined following iv administration using cremophor/
ethanol/water (10:10:80) at a MTD efficacious dose of
24 mg/kg. Serial blood samples were collected out to 8
h, and the separated plasma was analyzed for parent
drug by UV/HPLC. The clearance is low, 5.2 mL/min-1
kg-1, and may be saturated at this dose, with a terminal
half-life of 2.3 h and a moderate volume of distribution
of 0.44 L/kg. Analogue 1 also exhibits good in vitro
metabolic stability when incubated with human liver
microsomes.
The superiority of 1 over CPT-11 as an anticancer
agent was further demonstrated in the Lewis lung
carcinoma model (Figure 1). In this model 1 is active
over a range of three doses (20, 32, and 45 mg/kg) and
yields 6/8 cures at the MTD. Lewis lung carcinoma is a
particularly aggressive tumor model which is only
modestly responsive (as active as 1 at 13 mg/kg) to CPT-
11 and inactive to adriamycin (doxorubicin). On the
basis of these data, and the subsequent broad spectrum
antitumor activity of 1, which is equal or superior to
CPT-11 in other models such as murine M5076 sarcoma
and human xenografts HCT-116 colon and PC-3 pros-
tate carcinomas, 1 was nominated for clinical develop-
ment.
Acknowledgment. We thank Dr. Stella Huang and
Mr. Bill Cadiz for assistance with high field NMR and
low resolution mass spectra.
Supporting Information Available: Experimental de-
tails and analytical data are available for the preparation of
all compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
References
(1) (a) Long, B. H.; Balasubramanian, B. N. Non-Camptothecin
Topoisomerase I Active Compounds as Potential Anticancer
Agents. Exp. Opin. Ther. Pat. 2000, 10(5), 635-666. (b) Prud-
homme, M. Indolocarbazoles as Anti-Cancer Agents. Curr.
Pharm. Des. 1997, 3, 265-290.
(2) Shao, R.-G.; Cao, C.-X.; Shimizu, T.; O’Connor, P. M.; Kohn, K.
W.; Pommier, Y. Abrogation of an S-Phase Checkpoint and
Potentiation of Camptothecin Cytotoxicity by 7-Hydroxystauro-
sporine (UCN-01) in Human Cancer Cell Lines, Possibly Influ-
enced by p53 Function. Cancer Res. 1997, 57, 4029-4035.
Table 2 exemplifies the in vivo activity displayed by
the three analogues against HT29 human colon carci-
noma xenograft model when administered iv, in a 1:1:8
cremophor:ethanol:water vehicle. It is gratifying to see

Letters
(3) Krishnan, B. S.; Moore, M. E.; Lavoie, C. P.; Long, B. H.;
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 7 2261
70-74. (d) Xie, G.; Lown, J. W. A Facile Synthesis of Stauro-
sporine Aglycone. Tetrahedron Lett. 1994, 35, 5555-5558.
(9) (a) Ohkubo, M.; Kawamoto, H.; Ohno, T.; Nakano, M.; Mor-
ishima, H. Synthesis of NB-506, A New Anticancer Agent.
Tetrahedron 1997, 53, 585-592 (b) See ref 13. (c) Gallant, M.;
Link, J. T.; Danishefsky, S. J. A Stereoselective Synthesis of
Indole-â-N-Glycosides: An Application to the Synthesis of
Rebeccamycin. J. Org. Chem. 1993, 58, 343-349. (d) Link, J.
T.; Gallant, M.; Danishefsky, S. J. The First Synthesis of a Fully
Functionalized Core Structure of Staurosporine: Sequential
Indolyl Glycosidation by Endo and Exo Glycals. J. Am. Chem.
Soc. 1993, 115, 3782-3783.
(10) For the initial isolation and structure determination of novel
fluoroindolocarbazoles, see Lam, K. S.; Schroeder, D. R.; Veitch,
J. M.; Colson, K L.; Matson, J. A.; Rose, W. C.; Doyle, T. W.;
Forenza, S. Production, Isolation and Structure Determination
of Novel Fluoroindolocarbazoles from Saccharothrix aerocoloni-
genes ATCC 39243. J. Antibiot. 2001, 54, 1-9.
(11) Sugar 4 was prepared in four steps (26% yield), from 6′-fluoro-
1′,2′,3′,4′-tetra-(O)-acetyl-R-D-glucopyranose: (a) PhSH/BF3‚Et2O/
ClCH2CH2Cl. (b) K2CO3/CH3OH. (c) PhCH2Br/NaOH/BTEAC/
CH2Cl2. (d) Hg(OAc)2/THF/H2O.
(12) Sharma, M.; Korytnyk, W. A General and Convenient Method
for Synthesis of 6-Fluoro-6-deoxyhexose. Tetrahedron Lett. 1977,
18, 573-576.
(13) Wang, J.; Rosingana, M.; Watson, D. J.; Dowdy, E. D.; Discordia,
R. P.; Soundarajan, N.; Li, W.-S. Practical Synthesis of the
Rebeccamycin Aglycone and Related Analogues by Oxidative
Cyclization of Bisindolylmaleimides with a Wacker-Type Cata-
lytic System. Tetrahedron Lett. 2001, 42, 8935-8937.
(14) Ohkubo, M.; Nishimura, T.; Jona, H.; Honma, T.; Ito, S.;
Morishima, H. Synthesis of Indolocarbazole Glycosides Using
the Mitsunobu Reaction at the Glycosylation Step. Tetrahedron
1997, 53, 5937-5950.
(15) For a review of the chemistry in indolo[2,3-a]carbazole synthesis,
see Pindur, U.; Kim, Y.-S.; Mehrabani, F. Advances in Indolo-
[2,3-a]carbazole Chemistry: Design and Synthesis of Protein
Kinase C and Topoisomerase I Inhibitors. Curr. Med. Chem.
1999, 6, 29-69.
Dalterio, R. A.; Wong, H. S.; Rosenberg, I. E. Fluorescence
Polarization Studies of the Binding of BMS 181176 to DNA. J.
Biomol. Struct. Dyn. 1994, 12, 625-636.
(4) (a) Yoshinari, T.; Matsumoto, M.; Arakawa, H.; Okada, H.;
Noguchi, K.; Suda, H.; Okura, A.; Nishimura, S. Novel Antitu-
mor Indolocarbazole Compound 6-N-Formylamino-12,13-dihy-
dro-1,11-dihydroxy-13-(beta-D-glucopyranosyl)-5H-indolo[2,3-a]-
pyrrolo[3,4-c]carbazole-5,7(6H)-dione (NB-506): Induction of
Topoisomerase I-Mediated DNA Cleavage and Mechanisms of
Cell Line-Selective Cytotoxicity. Cancer Res. 1995, 55, 1310-
1315. (b) Arakawa, H.; Iguchi, T.; Morita, M.; Yoshinari, T.;
Kojiri, K.; Suda, H.; Okura, A.; Nishimura, S. Novel Indolocar-
bazole compound 6-N-formylamino-12,13-dihydro-1,11-dihydroxy-
13-(beta-D-glucopyranosyl)-5H-indolo[2,3-a]pyrrolo-[3,4-c]car-
bazole-5,7(6H)-dione (NB-506): Its Potent Antitumor Activities
in Mice. Cancer Res. 1995, 55, 1316-1320. (c) Fukasawa, K.;
Komatani, H.; Hara, Y.; Suda, H.; Okura, A.; Nishimura, S.;
Yoshinari, T. Sequence-Selective DNA Cleavage by a Topoi-
somerase I Poison, NB-506. Int. J. Cancer 1998, 75, 145-150.
(d) Yoshinari, T.; Ohkubo, M.; Fukasawa, K.; Egashira, S.; Hara,
Y.; Matsumoto, M.; Nakai, K.; Arakawa, H.; Morishima, H.;
Nishimura, S. Mode of Action of a New Indolocarbazole Anti-
cancer Agent, J-107088, Targeting Topoisomerase I. Cancer Res.
1999, 59, 4271-4275.
(5) Long, B. H.; Fairchild, C. A.; Bifano, M.; Kramer, R. Proc. Am.
Assoc. Cancer Res. 1997, 38, 775.
(6) Balasubramanian, B. N.; St. Laurent, D. R.; Saulnier, M. G.;
Long, B. H.; Bachand, C.; Beaulieu, F.; Clarke, W.; Deshpande,
M.; Eummer, J.; Fairchild, C. R.; Frennesson, D. B.; Kramer,
R.; Lee, F. Y.; Mahler, M.; Martel, A.; Naidu, B. N.; Rose, W. C.;
Russell, J.; Ruediger, E.; Solomon, C.; Stoffan, K. M.; Wong, H.;
Zimmermann, K.; Vyas, D. M. Design and Synthesis of a
Fluoroindolocarbazole Series as Selective Topoisomerase I Active
Agents. Discovery of Water-Soluble 3,9-Difluoro-12,13-dihydro-
13-[6-amino-â-D-glucopyranosyl]-5H,13H-benzo[b]-thienyl[2,3-a]-
pyrrolo[3,4-c]carbazole-5,7(6H)-dione (BMS-251873) with Cura-
tive Antitumor Activity against Prostate Carcinoma Xenograft
Tumor Model. J. Med. Chem. 2004, 47, 1609-1612.
(16) The 2′-fluoro-3′,4′,6′-tri-(O)-benzyl-D-glucopyranose (as a sepa-
rable 1:1 mixture of R,â-anomers) was synthesized from 3′,4′,6′-
tri-(O)-benzyl-D-glucal, using xenon difluoride in 6:1 acetonitrile:
water in 24% yield. For a relevant reference, see Hayashi, T.;
Murray, B. W.; Wang, R.; Wong, C.-H. A Chemoenzymatic
Synthesis of UDP-(2-deoxy-2-fluoro)galactose and Evaluation
of its Interaction with Galactosyltransferase Biorg. Med. Chem.
1997, 5, 497-500.
(7) Long, B. H.; Rose, W. C.; Vyas, D. M.; Matson, J. A.; Forenza,
S. Discovery of Antitumor Indolocarbazoles: Rebeccamycin, NSC
655649, and Fluoroindolocarbazoles. Curr. Med. Chem. - Anti-
Cancer Agents 2002, 2, 255-266.
(8) (a) Saulnier, M. G.; Frennesson, D. B.; Deshpande, M. S.; Vyas,
D. M. Synthesis of a Rebeccamycin-Related Indolo[2,3-a]carba-
zole by Palladium(0)-Catalyzed Polyannulation. Tetrahedron.
Lett 1995, 36, 7841-7844. (b) Brenner, M.; Rexhausen, H.;
Steffan, B.; Steglich, W. Pigments of Fungi, 57. Synthesis of
Arcyriarubin B and Related Bisindolylmaleimides. Tetrahedron
1988, 44, 2887-2892. (c) Brenner, M.; Mayer, G.; Terpin, A.;
Steglich, W. Pigments from Fungi. 67. Total Syntheses of the
Slime Mold Alkaloid Arcyriacyanin A. Chem. Eur. J. 1997, 3,
(17) The 2′-fluorogluco isomer of 1 is 5-fold more topo I potent than
CPT, yet is poorly cytotoxic vs P388 cells (IC50 ) 1500 nM). Poor
cell permeability of this 2′-fluoro analogue may account for its
weak cytotoxicity.
JM049090Z