Synthesis and biological activity of some structural modifications of pancratistatin

Article abstract of DOI:10.1016/j.bmcl.2004.03.032

Structurally modified derivatives of 7-deoxypancratistatin have been synthesized and evaluated in cancer cell line inhibition studies.

Full text of DOI:10.1016/j.bmcl.2004.03.032

Bioorganic & Medicinal Chemistry Letters 14 (2004) 2911–2915
Synthesis and biological activity of some structural
modifications of pancratistatin
Uwe Rinner,a Heather L. Hillebrenner,a David R. Adams,a Tomas Hudlickyb,*
and George R. Pettitc,ꢀ
aDepartment of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
bDepartment of Chemistry, Brock University, 500 Glenridge Avenue, St. Catharines, Ont., Canada L2S 3A1
cDepartment of Chemistry and Biochemistry and the Cancer Research Institute, Arizona State University, Tempe, AZ 85287, USA
Received 29 January 2004; revised 6 March 2004; accepted 12 March 2004
Abstract—Structurally modified derivatives of 7-deoxypancratistatin have been synthesized and evaluated in cancer cell line inhi-
bition studies.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
in isocarbostyril 1 that are essential to the activity of the
compounds against various cancer cell lines. Recently,
Pancratistatin (1) and 7-deoxypancratistatin (2), along
with their congeners narciclasine (3) and lycoricidine (4),
Figure 1, belong to the Amaryllidaceae group of natural
products that continues to attract high levels of atten-
tion.1–5 Although 1 and 3 possess promising antitumor
activities6 much remains to be known about the precise
mode of action of these natural products.6c;d;7 Some of
the recent insights include inhibition of the cell cycle
from G0/G1 to S phase6g and the powerful antiparasite
activity shown by pancratistatin.6h;i The search for more
bioavailable derivatives as well as attempts to identify
the pharmacophore8 of 1 led to a number of truncated
as well as unnatural derivatives in these series. Most
notable efforts have been published from the groups of
Pettit et al.8a and McNulty et al.,8b in addition to limited
investigations from our group already published.8c Re-
cently an unnatural derivative containing a sugar motif
was reported by Fessner and co-workers with biological
evaluation pending.9
OH
OH
HO
OH
OH
OH
OH
O
O
O
O
NH
NH
R
O
R
O
1 R = OH pancratistatin
3 R = OH narciclasine
2 R = H 7-deoxypancratistatin
4 R = H lycoricidine
OH
HO
OH
OH
OH
MeO
O
O
OH
NH
OH
NH
O
O
5
6
OH
HO
OH
OH
HO
OH
OH
The biological activity of truncated derivatives is lim-
ited, and the search continues to identify those elements
R
R
NH
NH
X
OMe
O
O
Keywords: Pancratistatin; Amaryllidaceae alkaloids; Enantioselective
synthesis; Anticancer drugs.
7
8 X = CH, N
R = OMe or hetero-
aromatic ring
* Corresponding author. Tel.: +1-905-688-5550x4956; fax: +1-905-984-
4841; e-mail addresses: thudlicky@brocku.ca; bpettit@asu.edu
ꢀ
Figure 1. Important members of the Amaryllidaceae group and trun-
cated or unnatural derivatives of 1 and 2.
Author to whom correspondence regarding biological activity studies
should be addressed.
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.03.032

2912
U. Rinner et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2911–2915
we established that the cis-isomer of 2 is inactive com-
pared to the trans-fused natural product.10 Little is
known about the precise mode of action of pancratist-
atin and only limited results are available about the
interaction of narciclasine with RNA.6c;d From currently
available data it appears that at least one or two
hydroxyl groups of the aminocyclitol ring are essential8b
as is the full aromatic portion and the donor–acceptor
hydrogen bonding system of the enolized b-ketoamide
contained in 1.
OH
OAc
O
O
O
O
OH
a, b
OAc
NHCO2Me
NHCO2Me
9
10
c
OH
OAc
OAc
O
O
O
O
To probe this issue further we chose to synthesize
truncated derivatives 5, 6, and 7 as well as compounds of
type 8, Figure 1, in which the piperonyl residue is re-
placed by various heteroaromatic nuclei presenting both
size and donor–acceptor hydrogen bonding attributes of
pancratistatin. In these compounds, the systematic
replacement or deletion of functionality should provide
further insight into the activity issues. Herein we report
the synthesis and evaluation of 5 and 6, Figure 1, along
with some of the intermediates.
OH
NH
d
NH
O
O
5
11
Scheme 1. Total synthesis of truncated derivative 5. Reagents and
conditions: (a) Ac2O, py, 98%; (b) H2, Pd/C, EtOH, 95%; (c) Tf2O,
DMAP, CH2Cl2, 4 °C, 50%; (d) NaOCH3, CH3OH, 70%.
with the lithio derivative of 3-bromoanisole to yield 13.2e
The synthesis proceeded well in analogy to previous
experience to the stage of 15 where the Banwell et al.
procedure11 for closure was utilized. Based on the report
by Magnus et al.2h in which similar closures generated
7:1 and 3:1 mixtures of regioisomers when C-7 position
featured methoxy and acetoxy groups, respectively. We
had hoped that both compounds 6 and 7 would become
accessible by this strategy via the expected nonselective
condensation with the intermediate isocyanate. To our
surprise, only 17 was produced regioselectively in these
closures and was transformed to 6 by deprotection of
the acetate groups. We failed to detect the other isomer,
16, in the reaction mixtures.
The synthesis of 5 was straightforward and was based
on the interception and adaptation of a known proce-
dure from our previous synthesis of 7-deoxypancratist-
atin, Scheme 1.3d Diol 9 was prepared as described
previously3d and acetylated (98%) prior to its hydroge-
nation to 10. Modified Bischler–Napieralski closure was
effected with Tf2O/DMAP3d;11 to furnish amide 11 in
50% yield, which was treated with MeOH/MeONa to
give 5 (85%).
Methoxy derivative 6 was prepared as shown in Scheme
2, following the strategy employed in the synthesis of 7-
deoxypancratistatin, namely the opening of aziridine 12
OH
O
OH
HO
OH
O
O
O
O
OH
a
b
d,c
OH
NHCO2Me
NHCO2Me
NHCO2Me
N
OMe
OMe
OMe
CO2Me
12
13
14
15
e,f
OH
OAc
OAc
HO
OH
OH
AcO
AcO
OAc
OAc
OAc
MeO
MeO
g
OAc
+
NH
NH
NH
O
O
OMe O
16 not observed
6
17
Scheme 2. Total synthesis of truncated derivative 6. Reagents and conditions: (a) i. 3-bromo anisole, n-BuLi, THF, )78 °C; ii. CuCN, 2 h; iii. 12,
BF3ÆEt2O, )78 °C to rt, 50%; (b) AcOH, THF, H2O, 60 °C, 76%; (c) t-BuOOH, VO(acac)2, C6H6, 60 °C, 22%; (d) NaOBz, H2O, reflux, 54%; (e)
Ac2O, py, 88%; (f) i. DMAP, Tf2O, CH2Cl2, 4 °C; ii. THF, HCl (2 M), 76%; (g) NaOCH3, THF, rt, 85%.

U. Rinner et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2911–2915
2913
steric rather than electronic arguments. It may be
interesting to repeat the reaction with the free phenol in
which the product of the closure from C-6a would be
stabilized by an intramolecular hydrogen bond.
10
10
10
MeO
O
O
6a
6a
6a
N
C
O
N
C
O
N
C
O
OMe
18
Figure 2. Regioselectivity of ring closure reactions.
OMe
19a
19b
2. Biological evaluation
The cancer cell line growth inhibition activity of the new
compounds with structural modifications of pancratist-
atin was tested against the natural isocarbostyril (1) and
narciclasine (3) (Table 1). Only the compounds pos-
sessing the complete ring system and stereochemistry of
pancratistatin, namely modification 6, displayed signi-
ficant activity, albeit some 10-fold less than 7-deoxy-
In the intermediate 18, Figure 2, employed by Magnus
C-6a and C-10 are similarly activated toward reaction
with the isocyanate, albeit with 7:1 or 3:1 selectivity for
the more reactive ortho position at C-6a. It appears that
in anisoles 19 the para attack is preferred (19b) based on
Table 1. Murine P388 lymphocytic leukemia and human cancer cell biology data for truncated derivative 6, synthetic intermediates, and 7-
deoxypancratistatin and pancratistatin for comparison
Compound
Murine P388 lymphocytic leukemia and human cancer cell results [lg/mL]
Murine P388 lym-
phocytic leukemia
Pancreas
BXPC-3
Breast
MCF-7
CNS
SF-268
Lung
NCI-H460
Colon
KM20L2
Prostate
DU-145
OAc
AcO
OAc
OAc
19.3
>10
>10
>10
>10
>10
>10
NHCO2Me
OMe
20
OAc
AcO
OAc
OAc
MeO
2.1
>10
4.6
>10
>10
>10
6.7
NH
O
17
OH
HO
OH
OH
MeO
4.3
4.9
4.4
3.3
2.8
3.6
2.6
NH
O
6
OAc
O
O
OAc
1.10
>10
>10
>10
>10
>10
>10
NH
O
11
OH
OH
O
O
1.39
>10
>10
>10
>10
>10
>10
NH
O
5
(continued on next page)

2914
U. Rinner et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2911–2915
Table 1. (continued)
Compound
Murine P388 lymphocytic leukemia and human cancer cell results [lg/mL]
Murine P388 lym-
phocytic leukemia
Pancreas
BXPC-3
Breast
MCF-7
CNS
SF-268
Lung
NCI-H460
Colon
KM20L2
Prostate
DU-145
OH
HO
OH
OH
O
O
0.039
0.028
0.032
0.017
0.048
0.062
0.016
NH
OH
OH
O
1a
HO
OH
OH
O
O
0.44
0.29
0.22
NH
O
2a
OH
NH
OH
OH
0.0012
0.026
0.019
0.021
0.032
0.021
0.011
O
O
OH
O
3a
a For the listed activities see Ref. 6h.
pancratistatin (100-fold less than 1). Deletion of two of
the four alcohol groups provided compounds 30-fold
less active in the cancer cell inhibition. Compound 5, its
acetate 11 and compound 6 showed activities in P388
lines an order of magnitude lower than that of 7-de-
oxypancratistatin. The fully hydroxylated derivative 6
also displayed activities in all human cancer cell lines
tested; compound 5 lacking the trans-diol unit was
inactive in these lines.
grateful to the National Science and Engineering
Council (NSERC), Canadian Foundation for Innova-
tion, and the Ontario Innovation Trust. One of us
(G.R.P.) also wishes to thank for financial support grant
R01-CA90441-02-03 with the Division of Cancer
Treatment and Diagnosis, NCI, DHHS, the Arizona
Disease Control Research Commission, Dr. Alec D.
Keith, the Robert B. Dalton Endowment Fund, and for
other assistance Dr. Jean-Charles Chapuis.
3. Conclusion
References and notes
It is clear from this and previous studies that enhanced
activity in pancratistatin-type compounds cannot be
expected in compounds that do not have the completely
functionalized cyclitol ring or that lack the full phe-
nanthridone nucleus. Future endeavors will focus on
synthesis and evaluation of derivatives of type 8 in
which the aminoinositol motif is preserved.
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Acknowledgements
€
Hudlicky, T.; Tian, X. R.; Konigsberger, K.; Maurya, R.;
The authors thank the National Science Foundation
(NSF) (CHE-9910412), the donors of the Petroleum
Research Fund administered by the American Chemical
Society (PRF-38075-AC), TDC Research Inc., and
TDC Research Foundation for generous financial sup-
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