Solution phase combinatorial chemistry. Synthesis of novel linear pyridinopolyamine libraries with potent antibacterial activity

Article abstract of DOI:10.1021/jo970535j

Novel linear pyridinopolyamine derivatives 1-3, 7, and 8 have been synthesized as scaffolds for combinatorial drug discovery. The mono-t-Boc- and monotosyl-protected linear scaffolds 1 and 2 were obtained by a Schiff base type cyclization of 2,6-pyridinedicarboxaldehyde (24) with monoprotected triamines 22 and 23 using Ni²⁺ as a metal template, followed by reductive cleavage and decomplexation in a one-pot procedure. The unprotected linear scaffold 3 was obtained by treating 1 with TFA. Scaffold 1 was also synthesized from the orthogonally protected pyridinepolyamine 7 which was constructed from 2,6-bis(bromomethyl)pyridine (29) in four steps. Selective deprotection of the key intermediate 7 afforded 8, which was further selectively deprotected to give scaffold 1. A combinatorial chemistry strategy involving solution phase simultaneous addition of functionalities (SPSAF) is described. Thirteen high-purity tertiary amine libraries (9-21) (total 1638 compounds) were synthesized by the SPSAF and fix last methodologies from linear polyamine scaffolds 1 and 2. All libraries were examined by TLC, purified by chromategraphic techniques, and characterized by ¹H NMR and ESI MS spectral data. A fix last methodology was utilized to minimize chemical reactions and perform SAR studies directly on libraries. Several first-round sublibraries of scaffold 1, containing 126 compounds each, exhibited potent antibacterial activity with MICs of 1-12 μM against Streptococcus pyogenes and Escherichia coli imp^-.

Full text of DOI:10.1021/jo970535j

5156
J . Org. Chem. 1997, 62, 5156-5164
Solu tion P h a se Com bin a tor ia l Ch em istr y. Syn th esis of Novel
Lin ea r P yr id in op olya m in e Libr a r ies w ith P oten t An tiba cter ia l
Activity
Haoyun An,* Becky D. Haly, Allister S. Fraser, Charles J . Guinosso, and P. Dan Cook
Isis Pharmaceuticals, Inc., 2292 Faraday Avenue, Carlsbad, California 92008
Received March 24, 1997X
Novel linear pyridinopolyamine derivatives 1-3, 7, and 8 have been synthesized as scaffolds for
combinatorial drug discovery. The mono-t-Boc- and monotosyl-protected linear scaffolds 1 and 2
were obtained by a Schiff base type cyclization of 2,6-pyridinedicarboxaldehyde (24) with
monoprotected triamines 22 and 23 using Ni2+ as a metal template, followed by reductive cleavage
and decomplexation in a one-pot procedure. The unprotected linear scaffold 3 was obtained by
treating 1 with TFA. Scaffold 1 was also synthesized from the orthogonally protected pyridinopo-
lyamine 7 which was constructed from 2,6-bis(bromomethyl)pyridine (29) in four steps. Selective
deprotection of the key intermediate 7 afforded 8, which was further selectively deprotected to
give scaffold 1. A combinatorial chemistry strategy involving solution phase simultaneous addition
of functionalities (SPSAF) is described. Thirteen high-purity tertiary amine libraries (9-21) (total
1638 compounds) were synthesized by the SPSAF and fix last methodologies from linear polyamine
scaffolds 1 and 2. All libraries were examined by TLC, purified by chromatographic techniques,
1
and characterized by H NMR and ESI MS spectral data. A fix last methodology was utilized to
minimize chemical reactions and perform SAR studies directly on libraries. Several first-round
sublibraries of scaffold 1, containing 126 compounds each, exhibited potent antibacterial activity
with MICs of 1-12 µM against Streptococcus pyogenes and Escherichia coli imp-.
In tr od u ction
tion of chemical libraries of small organic molecules.9-11
Along with this new direction, a variety of solid support
synthesis techniques have evolved.11,12 Interestingly,
solution phase combinatorial methodologies, relative to
solid support procedures, have not been widely
Combinatorial chemistry has received considerable
attention as a potential tool for drug discovery and lead
optimization.1,2 Initial combinatorial libraries have been
composed of a variety of oligomeric materials such as
peptides,3 nucleotides,4 saccharides,5 ureas,6 peptoids,7
and carbamates8 obtained from solid phase synthesis.
However, since oligomeric materials generally have
unfavorable pharmacokinetic properties as therapeutic
agents, more recent efforts have focused on the genera-
(5) (a) Danishefsky, S. J .; McClure, K. F.; Randolph, J . T.; Ruggeri,
R. B.; Science 1993, 260, 1307. (b) Yan, L.; Taylor, C. M.; Goodnow,
R., J r.; Kahne, D. J . Am. Chem. Soc. 1994, 116, 6953. (c) Rademann,
J .; Schmidt, R. R. Tetrahedron Lett. 1996, 37, 3989. (d) Wang, Z.-G.;
Douglas, S. P.; Krepinsky, J . J . Tetrahedron Lett. 1996, 37, 6985. (e)
Liang, R.; Yan, L.; Loebach, J .; Ge, M.; Uozumi, Y.; Sekanina, K.;
Horan, N.; Gildersleeve, J .; Thompson, C.; Smith, A.; Biswas, K.; Still,
W. C.; Kahne, D. Science 1996, 274, 1520. (f) Ding, Y.; Labbe, J .; Kanie,
O.; Hindsgaul, O. Bioorg. Med. Chem. 1996, 4, 683.
X Abstract published in Advance ACS Abstracts, J uly 1, 1997.
(1) (a) Still, W. C. Acc. Chem. Res. 1996, 29, 155. (b) Ohlmeyer, M.
H. J .; Swanson, R. N.; Dillard, L. W.; Reader, J . C.; Asouline, G.;
Kobayashi, R.; Wigler, M.; Still, W. C. Proc. Natl. Acad. Sci. U.S.A.
1993, 90, 10922. (c) Ostresh, J . M.; Husar, G. M.; Blondelle, S. E.;
Do¨rner, B.; Weber, P. A.; Houghten, R. A. Proc. Natl. Acad. Sci. U.S.A.
1994, 91, 11138. (d) Eichler, J .; Houghten, R. A. Mol. Med. Today
1995, 174. (e) Pinilla, C.; Appel, J .; Blondelle, S. E.; Dooley, C.; Do¨rner,
B.; Eichler, J .; Ostresh, J . M.; Houghten, R. A. Biopolymers (Peptide
Science) 1995, 37, 221. (f) Blondelle, S. E.; Houghten, R. A. Trends
Biotechnol. 1996, 14, 60. (g) Rinnova, M.; Lehl, M. Collect. Czech.
Chem. Commun. 1996, 61, 171.
(2) (a) Gallop, M. A.; Barrett, R. W.; Dower, W. J .; Fodor, S. P. A.;
Gordon, E. M. J . Med. Chem. 1994, 37, 1233. (b) Gordon, E. M.;
Barrett, R. W.; Dower, W. J .; Fodor, S. P. A.; Gallop, M. A. J . Med.
Chem. 1994, 37, 1385. (c) Terrette, N. K.; Gardner, M.; Gordon, D.
W.; Kobylecki, R. J .; Steele, J . Tetrahedron 1995, 51, 8135. (d) Terrett,
N. K.; Bojanic, D.; Brown, D.; Bungay, P. J .; Gardner, M.; Gordon, D.
W.; Mayers, C. J .; Steele, J . Bioorg. Med. Chem. Lett. 1995, 5, 917. (e)
Holmes, C. P.; Chinn, J . P.; Look, G. C.; Gordon, E. M.; Gallop, M. A.
J . Org. Chem. 1995, 60, 7328. (f) Frank, R. J . Biotechnol. 1995, 41,
259. (g) Lowe, G. Chem. Soc. Rev. 1995, 309.
(3) (a) Houghten, R. A.; Pinilla, C.; Blondelle, S. E.; Appel, J . R.;
Dooley, C. T.; Cuervo, J . H. Nature 1991, 354, 84. (b) J ung, G.; Beck-
Sickinger, A. G. Angew. Chem., Int. Ed. Engl. 1992, 31, 367. (c)
Houghten, R. A. METHODS: A Comparrion to Methods in Enzymology
1994, 6, 354. (d) Houghten, R. A. Proc. Natl. Acad. Sci. U.S.A. 1985,
82, 5131.
(4) (a) Ecker, D. J .; Vickers, T. A.; Hanecak, R.; Driver, V.; Anderson,
K. Nucleic Acids Res. 1993, 21, 1853. (b) Wyatt, J . R.; Vickers, T. A.;
Roberson, J . L.; Buckheit, R. W., J r.; Klimkait, T.; De Baets, E.; Davis,
P. E.; Rayner, B.; Imbach, J . L.; Ecker, D. J . Proc. Natl. Acad. Sci.
U.S.A. 1994, 91, 1356. (c) Lashkari, D. A.; Hunicke-Smith, S. P.;
Norgren, R. M.; Davis, R. W.; Brennan, T. Proc. Natl. Acad. Sci. U.S.A.
1995, 92, 7912.
(6) Nicolaou, K. C.; Flo¨rke, H.; Egan, M. G.; Barth, T.; Estevez, V.
A. Tetrahedron Lett. 1995, 36, 1775.
(7) (a) Simon, R. J .; Kania, R. S.; Zuckermann, R. N.; Huebner, V.
D.; J ewll, D. A.; Banville, S.; Ng, S.; Wang, L.; Rosenberg, S.; Marlowe,
C. K,; Spellmeyer, D. C.; Tan, R.; Frankel, A. D.; Santi, D V.; Cohen,
F. E.; Bartlett, P. A. Proc. Natl. Acad. Sci. U.S.A. 1992, 89, 9367. (b)
Zuckermann, R. N.; Martin, E. J .; Spellmeyer, D. C.; Stauber, G. B.;
Shoemaker, K. R.; Kerr, J . M.; Figliozzi, G. M.; Goff, D. A.; Siani, M.
A.; Simon, R. J .; Banville, S. C.; Brown, E. G.; Wang, L.; Richter, L.
S.; Moos, W. H. J . Med. Chem. 1994, 37, 2678.
(8) (a) Cho, C. Y.; Moran, E. J .; Cherry, S. R.; Stephans, J . C.; Fodor,
S. P. A.; Adams, C. L.; Sundaram, A.; J acobs, J . W.; Schultz, P. G.
Science 1993, 261, 1303. (b) Hsieh-Wilson, L. C.; Xiang, X.-D.; Schultz,
P. G. Acc. Chem. Res. 1996, 29, 164. (c) Paikoff, S. J .; Wilson, T. E.;
Cho, C. Y., Schulz, P. G. Tetrahedron Lett. 1996, 37, 5653.
(9) (a) Ellman, J . A. Acc. Chem. Res. 1996, 29, 132. (b) Thompson,
L. A.; Ellman, J . A. Chem. Rev. 1996, 96, 555. (c) Gordon, E. M.;
Gallop, M. A.; Patel, D. V. Acc. Chem. Res. 1996, 29, 144. (d) Gordon,
E. M. Curr. Opin. Biotechnol. 1995, 6, 624.
(10) (a) Patek, M.; Drake, B.; Lebl, M. Tetrahedron Lett. 1994, 35,
9169. (b) Zhang, C.; Moran, E. J .; Woiwode, T. F.; Short, K. M.; Mjalli,
A. M. M. Tetrahedron Lett. 1996, 37, 751. (c) Sarshar, S.; Siev, D.;
Mjalli, A. M. M. Tetrahedron Lett. 1996, 37, 835.
(11) (a) Wipf, P.; Cunningham, A.; Rice, R. L.; Lazo, J . S. Bioorg.
Med. Chem. 1997, 5, 165. (b) Harada, T.; Katada, J .; Tachiki, A.; Asari,
T.; Iijima, K.; Uno, I.; Ojima, I.; Hayashi, Y. Bioorg. Med. Chem. Lett.
1997, 7, 209. (c) Gray, N. S.; Kwon, S.; Schultz, P. G. Tetrahedron
Lett. 1997, 38, 1161.
(12) (a) Han, H.; Wolfe, M. M.; Brenner, S.; J anda, K. D. Proc. Natl.
Acad. Sci. U.S.A. 1995, 92, 6419. (b) Nefzi, A.; Ostresh, J . M.; Meyer,
J .-P.; Houghten, R. A. Tetrahedron Lett. 1997, 38, 931. (c) Armstrong,
R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating, T. A. Acc.
Chem. Res. 1996, 29, 123. (d) Weber, L.; Wallbaum, S.; Broger, C.;
Gubernator, K. Angew. Chem., Int. Ed. Engl. 1995, 34, 2280.
S0022-3263(97)00535-5 CCC: $14.00 © 1997 American Chemical Society

Pyridinopolyamine Libraries
J . Org. Chem., Vol. 62, No. 15, 1997 5157
explored.13-15 Furthermore, combinatorial chemistry
research has primarily focused on polypeptide backbones
and known pharmacophores.16-19 In contrast to these
approaches, we have elected to not base our combinatorial
libraries on known structures or pharmacophores but to
search novel structure space with a variety of scaffolds
which provide various shapes (footprints). Also, we
believe solution phase procedures offer significant ad-
vantages over solid phase methods20 and we have re-
cently described a new solution phase simultaneous
addition of functionalities (SPSAF) combinatorial strat-
egy for the preparation of chemical libraries.21,22 By this
approach, a series of high-purity libraries were generated
from unsymmetrical, novel polyazaphane scaffolds. One
of these polyazaphanes was prepared containing an
oxyamine (N-O) moiety in the polyamine portion of the
polyazaphane which provides a cleavable linkage for
generating libraries from libraries.
In the present work, we have elected to isolate the
linear unsubstituted scaffold that would be generated
from the polyazaphane by a libraries from libraries
approach and combinatorialize it directly according to the
SPSAF approach. This required the design and synthesis
of linear pyridinopolyamines scaffolds 1-3 (Figure 1).
After model studies based on the synthesis of small
libraries which could be carefully analyzed, 13 high-
purity linear tertiary amine libraries (9-21) (Figure 1,
Schemes 5 and 6) were synthesized from scaffolds 1 and
2 by the SPSAF approach. Initial antibacterial screening
results of the first-round sublibraries are also disclosed.
Resu lts a n d Discu ssion
The monoprotected triamines 22 and 2323 were cyclized
with 2,6-pyridinedicarboxaldehyde (24) by using Ni2+
(13) (a) Carell, T.; Wintner, E. A.; Bashir-Hashemi, A.; Rebek, J .,
J r. Angew. Chem., Int. Ed. Engl. 1994, 33, 2059. (b) Carell, T.;
Wintner, A.; Rebek, J ., J r. Angew. Chem., Int. Ed. Engl. 1994, 33, 2061.
(c) Carell, T.; Wintner, E. A.; Sutherland, A. J .; Rebek, J ., J r.;
Dunayevskiy, Y. M.; Vouros, P. Chem. Biol. 1995, 2, 171. (d) Shipps,
G. W., J r.; Spitz U. P.; Rebek, J ., J r. Bioorg. Med. Chem. 1996, 4, 655.
(14) (a) Boger, D. L.; Tarby, C. M.; Myers, P. L.; Caporale, L. H. J .
Am. Chem. Soc. 1996, 118, 2109. (b) Cheng, S.; Comer, D. D.; Williams,
J . P.; Myers, P. L.; Boger, D. L. J . Am. Chem. Soc. 1996, 118, 2567. (c)
Cheng, S.; Tarby, C. M.; Comer, D. D.; Williams, J . P.; Caporale, L.
H.; Myers, P. L.; Boger, D. L. Bioorg. Med. Chem. 1996, 4, 727.
(15) (a) McDevitt, J . P.; Lansbury, P. T., J r. J . Am. Chem. Soc. 1996,
118, 3818. (b) Smith, P. W.; Lai, J . Y. Q.; Whittington, A. R.; Cox, B.;
Houston, J . G.; Stylli, C. H.; Banks, M. N.; Tiller, P. R. Bioorg. Med.
Chem. Lett. 1994, 4, 2821. (c) Pirrung, M. C.; Chen, J . J . Am. Chem.
Soc. 1995, 117, 1240.
F igu r e 1. New linear pyridinopolyamine derivatives and
libraries.
(16) (a) Bunin, B. A.; Ellman, J . A. J . Am. Chem. Soc. 1992, 114,
10997. (b) Bunin, B. A.; Plunkett, M. J .; Ellman, J . A. Proc. Natl. Acad.
Sci. U.S.A. 1994, 91, 4708. (c) Plunkett, M. J .; Ellman, J . A. J . Am.
Chem. Soc. 1995, 117, 3306.
(17) (a) DeWitt, S. H.; Kiely, J . S.; Stankovic, C. J .; Schroeder, M.
C.; Reynolds Cody, D. M.; Pavia, M. R. Proc. Natl. Acad. Sci. U.S.A.
1993, 90, 6909. (b) Dressman, B. A.; Spangle, L. A.; Kaldor, S. W.
Tetrahedron Lett. 1996, 37, 937.
(18) (a) Ruhland, B.; Bhandari, A.; Gordon, E. M.; Gallop, M. A. J .
Am. Chem. Soc. 1996, 118, 253. (b) Gordon, D. W.; Steele, J . Bioorg.
Med. Chem. Lett. 1995, 5, 47. (c) Gordeev, M. F.; Patel, D. V.; Gordon,
E. M. J . Org. Chem. 1996, 61, 924.
(19) (a) Gordeev, M. F.; Patel, D. V.; Wu, J .; Gordon, E. M.
Tetrahedron Lett. 1996, 37, 4643. (b) MacDonald, A. A.; DeWitt, S.
H.; Hogan, E. M.; Ramage, R. Tetrahedon Lett. 1996, 37, 4815. (c)
Buckman, B. O.; Mohan, R. Tetrahedron Lett. 1996, 37, 4439. (d)
Smith, A. L.; Thomson, C. G.; Leeson, P. D. Bioorg. Med. Chem. Lett.
1996, 6, 1483. (e) Hutchins, S. M.; Chapman, K. T. Tetrahedron Lett.
1996, 37, 4865. (f) Mjalli, A. M. M.; Sarshar, S.; Baiga, T. J .
Tetrahedron Lett. 1996, 37, 2943. (g) Hutchins, S. M.; Chapman, K.
T. Tetrahedron Lett. 1996, 37, 4869.
cation as a metal template (Scheme 1). The cyclic nickel
complexes 25 were directly reduced by NaBH4 without
isolation. In this process, the Schiff base double bonds
were reduced along with reductive cleavage of the N-O
bond in the macrocyclic complexes to give complexes 26.
Direct decomplexation of 26 with NaCN followed by
NaOH treatment gave desired linear pyridinopolyamine
products 1 and 2 in 26% and 21% yields, respectively.
The linear structures of product 1 and 2 were established
by 1H and 13C NMR and HR(FAB) MS spectral data, and
combustion analyses. In order to characterize scaffolds
1 and 2, various derivatives were prepared (Schemes 1
and 2). Treatment of t-Boc-protected scaffold 1 with
trifluoroacetic acid (TFA) gave the corresponding com-
pletely deprotected scaffold 3. Compound 3 was reacted
with benzyl bromide under weak carbonate basic condi-
(20) (a) Curran, D. P. Chemtracts: Org. Chem. 1996, 9, 75. (b)
Curran, D. P.; Hoshino, M. J . Org. Chem. 1996, 61, 6480.
(21) An, H.; Cook, P. D. Tetrahedron Lett. 1996, 37, 7233.
(22) An, H.; Cummins, L. L.; Griffey, R. H.; Bharadwaj, R.; Haly,
B. D.; Fraser, A. S.; Wilson-LIngardo, L.; Risen, L. M.; Wyatt, J . R.;
Cook, P. D. J . Am. Chem. Soc. 1997, 119, 3696.
(23) Kung, P. P.; Guinosso, C. J .; Fraser, A. S.; Bharadwaj, R.; Cook,
P. D. Unpublished results.

5158 J . Org. Chem., Vol. 62, No. 15, 1997
An et al.
Sch em e 1
Sch em e 3
Sch em e 2
momethyl)benzoate. Compound 6 was further treated
with an excess amount of acetyl chloride. The hydroxyl
group of 6 was the only reactive site left and reacted with
acetyl chloride to give the corresponding ester 28. De-
rivatives 3-6, 27, and 28 were all characterized by NMR
and HRMS spectroscopic techniques. The structures of
these derivatives further confirmed the linear structure
of compounds 1 and 2. If the N-O bond in complexes
25 was not cleaved, the corresponding macrocyclic com-
pounds would be produced after decomplexation instead
of the linear compounds 1 and 2. The corresponding
macrocyclic compound of linear compound 1 was synthe-
sized by another method.21,22 The linear compound 1
showed completely different 1H and 13C NMR spectral
and chromatographic properties from those of the corre-
sponding macrocyclic compound.22
This one-pot procedure for the synthesis of scaffold 1
(Scheme 1) is convenient; however, starting material 22
is difficult to prepare.23 In order to fully utilize pyridi-
nopolyamine 1 for expanded combinatorial library studies
and for subsequent iterative deconvolutions, we have
designed another synthetic route (Scheme 3) which
provided scaffold 1 through the orthogonally protected
compound 7. The reaction of 2,6-bis(bromomethyl)pyri-
dine (29) with 1.1 equiv of potassium phthalimide (30)
using K2CO3 as the base gave 2-(bromomethyl)-6-(ph-
thalimidomethyl)pyridine (31). Treatment of N-(3-hy-
droxypropyl)ethylene diamine (32) with 1.0 equiv of
2-nitrobenzenesulfonyl chloride (33) in the presence of
diisopropylethylamine afforded the desired monopro-
tected product 34 in a 57% yield. Compound 34 was
tion to give the tetrabenzylated derivative 4. When
compound 1 was treated with excess benzoyl chloride in
the presence of Et3N, the corresponding tetrabenzoylated
product 27 was obtained (Scheme 2). When compound
1 was reacted with 1.98 equiv of methyl 3-(bromometh-
yl)benzoate, the trialkylated product 5 and dialkylated
product were isolated. The trialkylated product 6 was
also obtained by the reaction of 2 with methyl 3-(bro-

Pyridinopolyamine Libraries
J . Org. Chem., Vol. 62, No. 15, 1997 5159
Sch em e 4
treated with di-tert-butyl dicarbonate to give diprotected
product 35 in a 93% yield. Sulfonamide 35 was alkylated
with bromide 31 at rt under weak carbonate basic
condition. The orthogonally protected product 7 was
obtained in an 88% yield. This key intermediate (7)
contains three different protecting groups, each of which
can be selectively removed under mild conditions without
affecting the other two. Compound 7 was selectively
deprotected with hydrazine, providing the corresponding
diprotected product 8. Further selective deprotection of
compound 8 with thiophenol24 in the presence of K2CO3
gave the scaffold 1. Monoprotected compound 1 obtained
by this route shows the same chromatographic and
spectroscopic properties as those of compound 1 synthe-
sized by the previous route (Scheme 1). New compounds
1
31, 34, 35, 7, and 8 were all characterized by H and 13C
NMR and HRMS spectroscopies.
The unprotected parent scaffold 3 can be used as the
scaffold to make libraries directly; however, we elected
to use monoprotected derivatives 1 and 2 as scaffolds in
a fix last combinatorial methodology which allows itera-
tive deconvolution. Six different benzyl bromide deriva-
tives (see Figure 1 for structural details) have been
determined by capillary electrophoresis techniques to be
desirable functionalities (electrophiles) to add in a si-
multaneous manner.22
Model studies with two functionalities (Scheme 4) were
first carried out in order to find appropriate reaction,
workup, and chromatographic conditions for each library
preparation step. Electrophiles R2Br (BrCH2C6H4CH3-
m) and R5Br (BrCH2C6H4COOCH3-m) were chosen as
initial functionalities for model studies because the
quality of these libraries could readily be assessed by 1H
NMR due to the distinct methyl groups. In addition,
these differential electron-donating and -withdrawing
functional groups would represent the range of influences
of other groups. A equal molar mixture of R2Br and R5Br
(total 4 equiv) was added to a stirred mixture of scaffold
1 and anhydrous K2CO3 in CH3CN (Scheme 4). After
overnight reaction and general workup, the crude reac-
tion mixture was purified by flash chromatography25 on
a silica gel column to give pure library 36 in a 93% yield.26
Library 36 containing six compounds27 with four different
were not present in other libraries. The sodium con-
tamination, probably introduced during the workup, did
not influence the purity of libraries. Deprotection of
library 36 with TFA afforded intermediate library 37
which showed the expected four peaks in the MS spec-
trum. Library 37 was divided into two parts which were
treated with two selected electrophiles R2Br and R5Br
using K2CO3 as the base to give final libraries 38 and
39, respectively, after chromatographic purification. Li-
braries 38 and 39 were all confirmed by H NMR and
ESI MS spectra.
After successful preparation of model libraries from
scaffold 1 and selected functionalities, six functionalities
1
were used to prepare larger libraries (Scheme 5).
A
1
solution containing equal molar amounts of six benzylic
bromides RxBr (x ) 1-6, 1.0 mmol each for a total of 6.0
mmol, 3.6 equiv) in CH3CN was added to the reaction
mixture containing scaffold 1 and K2CO3. After overnight
reaction and aqueous workup, library 9 was obtained in
a 76% yield26 following flash chromatographic purifica-
tion. Combinatorialization of the three nitrogenous
reactive sites of scaffold 1 with six different functional-
ities results in a library containing 126 different com-
pounds instead of 216 (63) compounds because of the C2
symmetry of the primary amine.27 Library 9 was verified
by 1H NMR and ESI MS in which all peaks fall in a range
between the smallest molecular weight and the largest
molecular weight (see Experimental Section). Library 10
was similarly obtained in a 71% yield. Because the t-Boc
protecting group in library 9 is easily removed compared
to the tosyl group in library 10, the t-Boc-protected
intermediate library 9 was used for further preparation
of other sublibraries. Library 9 was treated with TFA
to afford the corresponding library 11 in a 95% yield. This
key intermediate library 11 with the last reactive site
was reacted with 1.5 equiv of benzyl bromide (R1Br) to
give the final library 12 in a 70% yield after preparative
thin layer chromatographic (TLC) purification.25 Final
molecular weights was confirmed by H NMR and ESI
1
MS spectral data.28 The H NMR spectrum of library 36
showed the right ratio for different protons in the library
and 1:1 ratio for CH3 and COOCH3 protons. ESI MS
spectrum showed all four peaks with expected masses
[M + H]+ and four [M + Na]+ peaks representing the
sodium contamination. The [M + Na]+ peaks generally
(24) Fukuyama, T.; J ow, C. K.; Chung, M. Tetrahedron Lett. 1995,
36, 6373.
(25) The column loaded with crude library was eluted with a less
polar solvent to remove the excess benzyl bromide derivatives and then
eluted with more polar solvents to completely remove the library. All
fractions containing library compounds were collected. The preparative
thin layer chromatography (PLC) loaded with crude library was
developed by selected solvents. The library band, which was wider
than those of general single compounds, was collected to provide pure
library without electrophiles and other impurities.
(26) The theoretical yield was calculated according to the average
molecular weight. The yield was obtained by comparing the amount
of isolated library with the theoretical yield.
(27) A scaffold with n unsymmetric sites was combinatorialized with
m functionalities to give a library containing mn compounds. A scaffold
with n sites and one C2 symmetric element was combinatorialized with
m functionalities to give a library containing [mn-1(m + 1)]/2 com-
pounds.
(28) The 1H NMR spectra of libraries show the right ratio of certain
protons. The ESI mass spectra show the peaks ranging from the
smallest molecular weight to the largest molecular weight in libraries.

5160 J . Org. Chem., Vol. 62, No. 15, 1997
An et al.
Ta ble 1.
Sch em e 5
Activity of Libr a r ies in Gr ow th In h ibition Assa ys
(MIC, µM)a
library complexity S. Pyogenes E. coli imp- C. albicans
9
10
11
12
13
14
15
16
17
18
19
20
21
2
126
126
126
126
126
126
126
126
126
126
126
126
126
1
>100
>100
1-5
1-5
>100
>100
>100
>100
>100
>100
>100
>100
1-5
1-5
>100
>100
>100
>100
>100
>100
5-25
5-25
5-12
12-25
5-12
5-25
5-25
5-25
25-50
>100
25-50
>100
>100
5-25
>100
>100
5-25
3
4
1
1
1-5
a
The MIC (minimum inhibitory concentration) value is given
as a range of library concentration (total concentration of com-
pounds in the libraries). After 24 h, complete growth was observed
at lower bound of the given MIC and no growth was observed at
the upper bound. Ampicillin and tetracycline were used as
antibacterial references for S. pyogenes and E. coli imp-. Am-
photericin B was used as antifungal reference for C. albicans.
increased polarity of the libraries. All libraries described
above were monitored by TLC, purified by chromato-
1
graphic techniques,25 and verified by H NMR and ESI
MS spectra.28 The fix last combinatorial methodology
allows SAR studies to be performed directly on libraries
and thus further increases the diversity. The function-
alities placed in the fixed position are “positionally
biased” in that they are not combinatorialized throughout
the other positions.
Sch em e 6
Table 1 shows the antibacterial activity of libraries
9-21 and single compounds 2-4 in growth inhibition
assays. The activity was expressed by minimum inhibi-
tory concentration (MIC) in µM. All samples were
screened against Streptococcus pyogenes and Escherichia
coli imp- bacterial antigrowth assays. The highest
concentration tested was 100 µM. At this concentration
libraries 9, 10, and 13-18 and compounds 2 and 3 did
not exhibit inhibition. Libraries 11 and 12 showed strong
inhibition against S. pyogenes and E. coli imp- with MIC
of 1-5 µM. Libraries 19-21 and tetrabenzyl-substituted
compound 4 were inhibitory against the bacteria with
MICs of 5-12 to 12-25 µM. Results from the Candida
albicans assay indicated that library 20 is more specific
against bacteria than other active libraries. Strong
inhibition of compound 4 against C. albicans indicated
its potent antifungal activity. These results indicated
that two of nine original libraries (9-17) and three of
four extended libraries (18-21) show potential antibacte-
rial activity against S. pyogenes and E. coli imp- with
MICs in the micromolar range. Even though only one
set of functionalities was described in this paper to
illustrate the SPSAF and fix last methodologies, various
other functionalities can easily be introduced to generate
other diverse libraries. A significant advantage of this
approach is that large quantities of libraries are readily
prepared which provide material for other assays and for
the conversion of one library into another library. Fur-
ther studies on the preparation of new libraries based
on this linear scaffold, biological screening for various
assays, and iterative deconvolution of active libraries will
be reported in due course.
libraries 13-17 were prepared under similar conditions
by parallel reactions of the intermediate library 11 with
five other functionalities RxBr (x ) 2-6). These libraries
differ by the functionality on the last fixed position as
required in our iterative deconvolution process. The ESI
mass spectrum of library 15 shows all 52 distinct peaks
out of 126 compounds in the range from the smallest
molecular weight 643 to the largest molecular weight 847.
Computer simulation22 of library 15 exhibits almost the
same mass spectrum (Supporting Information).
To introduce new functionalities and increase the
diversity of libraries, the intermediate library 11 having
the last position available was further reacted with
methyl R-bromoacetate (R7Br), bromoacetonitrile (R8Br),
and R-bromoacetamide (R9Br) under similar conditions
to afford the corresponding libraries 18, 19, and 20,
respectively (Scheme 6). Library 11 was reacted with
commercially available 2-chloro-N-methoxy-N-methylac-
etamide (R10Cl) at 50-60 °C for 24 h to give the library
21. More polar developing agents were used for prepara-
tive TLC purification of libraries 20 and 21 due to the

Pyridinopolyamine Libraries
J . Org. Chem., Vol. 62, No. 15, 1997 5161
gave 0.94 g (26%) of product 1 as a pale yellow oil: silica gel
TLC Rf 0.40 (30:1 MeOH-30% NH4OH); H NMR (CDCl3) δ
In conclusion, we have synthesized novel linear pyri-
dinopolyamine derivatives 1 and 2 by the cycliczation of
monoprotected triamines 22 and 23 with 2,6-pyridinedi-
carboxaldehyde (24) followed by reductive cleavage and
decomplexation in a one-pot procedure. Scaffold 1 was
also synthesized by another route through orthogonally
protected key intermediates 7 and 8. Intermediate 7
with three different protecting groups can be used for the
preparation of various combinatorial libraries and for the
deconvolution of active libraries to find lead compounds.
Scaffold 1 can be used to make various libraries with
different types of functionalities by different reactions.
Solution phase simultaneous addition of functionalities
(SPSAF) combinatorial approach was extensively utilized
to generate 13 libraries with high purity from the linear
scaffold. The quality of libraries was judged by TLC and
1H NMR and ESI MS spectroscopic techniques. Large
quantities of libraries are available for future screening.
A fix last combinatorial methodology was used to make
more diverse libraries, perform SAR studies directly on
libraries, and more effectively find active libraries. The
methodologies we described here can be used to generate
various other combinatorial libraries for drug discovery.
Libraries 11, 12, and 19-21 show potent antimicrobial
activity against S. pyogenes and E. coli imp- in MICs of
low µM ranges.
1
1.38 (s, 9H), 1.50-1.65 (m, 2H), 2.50 (br, 1H, ex D2O), 2.77 (t,
2H, J ) 6.2 Hz), 3.10-3.28 (m, 4H), 3.35-3.48 (m, 2H), 3.83
(s, 2H), 3.88 (s, 2H), 7.08 (d, 2H, J ) 7.5 Hz), 7.54 (t, 1H, J )
7.5 Hz); 13C NMR (CDCl3) δ 28.4, 31.0, 43.8, 47.7, 48.0, 54.9,
58.7, 79.9, 119.4, 120.2, 136.9, 156.5, 159.0, 161.4; MS (EI)
m/ z 338 (M)+; MS (CI+ and FAB+) m/ z 339 (M + 1)+; MS (CI-)
m/ z 337 (M - 1)-; HRMS (EI) m/ z 338.231 (M)+ (C17H30N4O3
requires 338.231). Anal. Calcd for C17H30N4O3: C, 60.33; H,
8.93. Found: C, 60.75; H, 8.86.
3-[[2-[[[6-(Am in om et h yl)-2-p yr id in yl]m et h yl]a m in o]-
eth yl](tosyl)a m in o]-1-p r op a n ol (2). Pyridinopolyamine 2
was prepared as above for 1 from 2323,29 (1.0 g, 3.8 mmol), 10
mL of EtOH, NiCl2‚6H2O (0.88 g, 3.7 mmol), 24 (0.5 g, 3.7
mmol), and 30 mL of EtOH-H2O (1:1). Chromatographic
purification of the crude product gave 0.30 g (21%) of product
2 as a pale yellow oil: silica gel TLC Rf 0.42 (30:1 MeOH-
1
30% NH4OH); H NMR (CDCl3) δ 1.65-1.80 (m, 2H), 2.36 (s,
3H), 2.77 (t, 2H, J ) 6.0 Hz), 3.05-3.20 (m, 4H), 3.55 (t, 2H,
J ) 5.7 Hz), 3.79 (s, 2H), 3.86 (s, 2H), 7.05 (d, 2H, J ) 7.6
Hz), 7.21 (d, 2H, J ) 8.0 Hz), 7.51 (t, 1H, J ) 7.6 Hz), 7.61 (d,
2H, J ) 8.0 Hz); 13C NMR (CDCl3) δ 21.5, 31.9, 46.7, 47.4,
48.1, 49.5, 54.5, 58.5, 119.7, 120.5, 127.3, 129.7, 135.7, 137.1,
143.4, 158.6, 161.0; HRMS (FAB) m/ z 393.197 (M + 1)+
(C19H29N4SO3 requires 393.196).
Anal.
Calcd for
C19H28N4O3S: C, 58.14; H, 7.19. Found: C, 58.08; H, 6.97.
3-[[2-[[[6-(Am in om et h yl)-2-p yr id in yl]m et h yl]a m in o]-
eth yl]a m in o]-1-p r op a n ol (3). CF3COOH (5 mL) was added
dropwise to a stirred solution of 1 (190 mg, 0.56 mmol) in 2
mL of CH2Cl2 at 0 °C. The resulting reaction mixture was
stirred at rt for 4 h. The solvent was evaporated, and the
residue was purified by flash chromatography on a silica gel
column. Elution with 100% MeOH and then 10:1 MeOH-30%
NH4OH afforded 75 mg (56%) of the title compound 3 as a
colorless oil: silica gel TLC Rf 0.40 (5:1 MeOH-30% NH4OH);
1H NMR (CDCl3) δ 1.57-1.72 (m, 2H), 2.57 (br, 5H), 2.65-
2.88 (m, 6H), 3.69 (t, 2H, J ) 5.6 Hz), 3.81 (s, 2H), 3.88 (s,
2H), 7.07 (dd, 2H, J ) 7.6, 2.8 Hz), 7.53 (t, 1H, J ) 7.6 Hz);
13C NMR (CDCl3) δ 31.3, 47.7, 48.8, 49.0, 49.4, 55.0, 63.2, 119.4,
120.3, 136.9, 159.22, 161.4; HRMS (FAB) m/ z 239.187 (M +
1)+ (C12H23N4O requires 239.187).
Exp er im en ta l Section
Proton and carbon NMR spectra were recorded at 199.975
MHz unless otherwise indicated. N5-(tert-Butoxycarbonyl)-1,7-
diamino-1-oxa-5-azaheptane (22)23 and N5-tosyl-1,7-diamino-
1-oxa-5-azaheptane (23)23,29 were prepared according to our
documented procedure. Other starting materials were pur-
chased from Aldrich and TCI America Chemical Companies.
The bacterial and yeast antigrowth assays were performed in
96-well plate format in 150 µL volume in the presence of
library or relevant antibiotic or antifungal controls.30 Growth
was monitored as a function of time by measuring absorbance
at 595 nm. The S. pyogenes strain was ATCC #14289 and was
grown in 1× Todd-Hewitt broth. The E. coli imp- strain was
a kind gift of Spencer Bensen and was grown in 1/2× LB.31
The C. albicans was ATCC #10231 and was grown in YM
media.
3-[[2-[[[6-(Am in om et h yl)-2-p yr id in yl]m et h yl]a m in o]-
eth yl](ter t-bu toxyca r bon yl)a m in o]-1-p r op a n ol (1). A so-
lution of 2223 (2.50 g, 10.7 mmol) in 15 mL of EtOH was added
to a stirred solution of NiCl2‚6H2O (2.55 g, 10.7 mmol) in 60
mL of EtOH-H2O (1:1). 2,6-Pyridinedicarboxaldehyde (24)
(1.45 g, 10.7 mmol) was added to the above blue solution
followed by glacial AcOH (1.0 mL). The resulting deep blue
solution was stirred at rt for 2 h and then at 80 °C for 6 h.
The solution was cooled to 0 °C, and then NaBH4 (2.0 g, 52.0
mmol) was added in portions. The reaction mixture was
stirred at rt overnight and at 80 °C for 2 h. The cooled reaction
mixture was concentrated under reduced pressure to remove
EtOH. The reaction mixture was diluted with 30 mL of H2O,
and NaCN (4.9 g, 100 mmol) was added. The resulting
mixture was stirred at 80 °C for 1 h. The cooled reaction
mixture was basified to pH 13-14 with aqueous NaOH and
then extracted with CHCl3. The combined organic phase was
washed with brine and dried (Na2SO4). The solvent was
evaporated under reduced pressure, and the residue was
purified by flash chromatography on a silica gel column.
Elution with 100% MeOH and then 100:1 MeOH-30% NH4OH
3-[[2-[Ben zyl[[6-[[d ib en zyla m in o]m et h yl]-2-p yr id in -
yl]m eth yl]a m in o]eth yl]ben zyla m in o]-1-p r op a n ol (4). A
mixture of 3 (37 mg, 0.155 mmol), anhydrous K2CO3 (0.20 g,
1.4 mmol), and benzyl bromide (78 µL, 112 mg, 0.66 mmol,
4.25 equiv) in 5 mL of anhydrous CH3CN and 2 mL of
anhydrous DMF was stirred at rt overnight. The solvent was
evaporated under vacuum, and the residue was dissolved in
H2O and CHCl3. The layers were separated, and the aqueous
layer was extracted with CHCl3. The combined organic phase
was washed with brine and dried (Na2SO4). The solvent was
evaporated, and the residue was purified by preparative thin
layer chromatography (PLC) on a silica gel plate using 15:1
EtOAc-MeOH as the developing agent affording 46 mg (51%)
of the title compound 4 as a pale yellow oil: silica gel TLC Rf
1
0.43 (20:1 EtOAc-MeOH); H NMR (CDCl3) δ 1.56-1.75 (m,
2H), 2.50-2.75 (m, 6H), 3.45-3.85 (m, 14H), 7.12-7.70 (m,
23H); HRMS (FAB) m/ z 599.377 (M + 1)+ (C40H47N4O requires
599.375).
3-[[2-[Ben zoyl[[6-[(b en zoyla m in o)m et h yl]-2-p yr id in -
yl]m et h yl]a m in o]et h yl](ter t-b u t oxyca r b on yl)a m in o]-1-
p r op yl Ben zoa te (27). Benzoyl chloride (0.5 mL, 0.71 g, 4.2
mmol) was added dropwise at rt to a stirred solution of 1 (40
mg, 0.11 mmol) in 5 mL of CHCl3 containing 0.5 mL of Et3N.
After being stirred at rt for 1 h, the reaction mixture was
diluted with CHCl3. The solution was washed with aqueous
NaHCO3 and brine. The dried (Na2SO4) CHCl3 solution was
concentrated under reduced pressure, and the residue was
purified by flash chromatography on a silica gel column.
Elution with 1:1 hexanes-EtOAc and then 100% EtOAc
afforded 60 mg (78%) of the tribenzoylated derivative 27 as a
pale yellow oil: silica gel TLC Rf 0.30 (1:2 hexanes-EtOAc);
1H NMR (CDCl3) δ 1.34 (s, 9H), 1.70 (m, 2H), 3.20-3.70 (m,
6H), 4.25-4.38 (m, 2H), 4.74 (s, 2H), 4.77 (s, 2H), 7.00-8.10
(m, 18H); MS (ESI) m/ z 651 (M + 1)+, 673 (M + Na)+.
(29) An, H.; Guinosso, C. J .; Fraser, A. S.; Cook, P. D. J . Heterocyc.
Chem. Submitted.
(30) National Committee for Clinical Laboratory Standards. Methods
for Dilution Antimicrobial Susceptibility Tests for Bacterial that Grow
Aerobically, 1993, MCCLS Document M7-A3, Vol. 13, Villanova, PA.
(31) Sampson, B. A.; Misra, R.; Benson, S. A. Genetics 1989, 122,
491.

5162 J . Org. Chem., Vol. 62, No. 15, 1997
An et al.
P r ep a r a tion of Com p ou n d 5. Compound 5 was prepared
as above for 4 from 1 (100 mg, 0.29 mmol), K2CO3 (170 mg,
1.23 mmol), and methyl 3-(bromomethyl)benzoate (135 mg,
0.59 mmol, 1.98 equiv) in 17 mL of CH3CN. The crude product
was purified by flash chromatography on a silica gel column.
Elution with 1:1 hexanes-EtOAc and then 100% EtOAc
afforded 90 mg (39%) of tribenzylated product 5 as a colorless
HRMS (FAB) m/ z 331.007 (M + 1)+ (C15H12N2O2Br requires
331.008). Anal. Calcd for C15H11N2O2Br: C, 54.40; H, 3.35;
N, 8.46. Found: C, 54.29; H, 3.33; N, 8.23.
3-[[2-[(2-Nitr oben zen esu lfon yl)a m in o]eth yl]a m in o]-1-
p r op a n ol (34). A solution of 2-nitrobenzenesulfonyl chloride
(33) (46.9 g, 211 mmol, 1.0 equiv) in 500 mL of CH2Cl2 was
added to a stirred solution of N-(3-hydroxypropyl)ethylenedi-
amine (32) (25.0 g, 211 mmol) and diisopropylethylamine (36.9
mL, 211 mmol) in 450 mL of CH2Cl2 at 0 °C by means of a
double-ended needle under an Ar atmosphere over a period of
0.5 h. The resulting reaction mixture was stirred at 0 °C for
1 h, quenched with H2O (400 mL), and extracted with CH2Cl2
(7 × 400 mL). The combined organic phase was washed with
brine, dried (Na2SO4), and concentrated under reduced pres-
sure. The residual oil was purified by flash chromatography
on a silica gel column. Elution with 100% EtOAc and then
3:7 EtOAc-MeOH afforded 36.78 g (57%) of the monoprotected
product 34 as a colorless oil: silica gel TLC Rf 0.47 (100:1
MeOH-30% NH4OH); 1H NMR (CDCl3, 400 MHz) δ 1.66-1.71
(m, 2H), 2.78-2.81 (m, 4H), 3.20 (t, 2H, J ) 5.6 Hz), 3.69 (br,
3H, ex D2O), 3.75 (t, 2H, J ) 5.6 Hz), 7.73-7.77 (m, 2H), 7.84-
7.86 (m, 1H), 8.12-8.15 (m, 1H); 13C NMR (CDCl3) δ 31.0, 42.9,
48.3, 48.4, 62.9, 125.3, 131.0, 132.7, 133.4, 133.6, 148.0; HRMS
(FAB) m/ z 304.096 (M + 1)+ (C11H18N3O5S requires 304.096).
3-[[2-[(2-Nit r ob en zen esu lfon yl)a m in o]et h yl](ter t-b u -
toxyca r bon yl)a m in o]-1-p r op a n ol (35). A solution of di-tert-
butyl dicarbonate (26.6 g, 122 mmol) in anhydrous THF (200
mL) was added to a stirred solution of 34 (36.8 g, 121 mmol)
and Et3N (34.0 mL, 244 mmol) in 200 mL of anhydrous THF
at 0 °C for 20 min. The resulting reaction mixture was stirred
at rt for 24 h and concentrated under reduced pressure. The
residue was treated with saturated NaHCO3 (300 mL), and
the mixture was extracted with CH2Cl2 (2 × 600 mL). The
combined organic phase was washed with brine, dried (Na2SO4),
and concentrated under reduced pressure. The residue was
purified by flash chromatography on a silica gel column.
Elution with 6:4 and then 1:4 hexanes-EtOAc afforded 45.6
g (93%) of compound 35 as a colorless oil which solidified upon
standing: mp 79-80 °C; silica gel TLC Rf 0.33 (1:4 hexanes-
EtOAc); 1H NMR (CDCl3, 400 MHz) δ 1.45 (s, 9 H), 1.60-1.78
(m, 2H), 3.21-3.40 (m, 6H), 3.45-3.70 (m, 2H), 5.85 (br, 1H),
7.74-7.89 (m, 3H), 8.08-8.15 (m, 1H); 13C NMR (CDCl3) δ
28.2, 30.6, 42.3, 44.0, 47.0, 58.4, 80.8, 125.2, 130.7, 132.7, 133.6,
1
oil: silica gel TLC Rf 0.52 (100% EtOAc); H NMR (CDCl3) δ
1.24 (s, 9H), 1.40-1.60 (m, 2H), 2.56-2.68 (m, 2H), 3.15-3.35
(m, 4H), 3.38-3.54 (m, 2H), 3.58-3.78 (m, 10H), 3.88, 3.89 (s,
9H), 7.30-7.48 (m, 4H), 7.50-7.70 (m, 4H), 7.83-8.07 (m, 6H);
13C NMR (CDCl3) δ 28.2, 30.5, 43.1, 45.0, 52.1, 57.9, 58.2, 58.7,
59.7, 60.4, 80.0, 121.0, 128.4, 129.7, 129.9, 130.2, 133.3, 137.1,
139.5, 139.7, 156.7, 158.7, 158.9, 167.1; MS (ESI) m/ z 783 (M
+ 1)+.
The column was further eluted with 10:1 and then 5:1
EtOAc-MeOH, giving 80 mg (42%) of the dibenzylated product
as pale yellow oil: silica gel TLC Rf 0.42 (5:1 EtOAc-MeOH);
1H NMR (CDCl3) δ 1.28 (s, 9H), 1.45-1.60 (m, 2H), 2.64 (t,
2H, J ) 6.5 Hz), 2.88 (br, 1H, NH), 3.15-3.32 (m, 4H), 3.38-
3.50 (m, 2H), 3.70 (s, 2H), 3.76 (s, 2H), 3.80-3.95 (m, 10H),
7.08-7.18 (m, 1H), 7.27-7.42 (m, 3H), 7.46-7.68 (m, 3H),
7.83-8.05 (m, 4H); MS (ESI) m/ z 635 (M + 1)+.
3-[[2-[3-(Meth oxyca r bon yl)ben zyl[[6-[[bis[(3-m eth oxy-
car bon yl)ben zyl]am in o]m eth yl]-2-pyr idin yl]m eth yl]am i-
n o]eth yl]tosyla m in o]-1-p r op a n ol (6). Derivative 6 was
prepared as above for 5 from 2 (130 mg, 0.33 mmol), methyl
3-(bromomethyl)benzoate (137 mg, 0.6 mmol), and K2CO3 (0.20
g, 1.4 mmol) in 8 mL of CH3CN. Chromatographic purification
afforded 110 mg (49%) of trisubstituted product 6 as a colorless
oil: silica gel TLC Rf 0.37 (1:2 hexanes-EtOAc); 1H NMR
(CDCl3) δ 1.48-1.60 (m, 2H), 2.35 (s, 3H), 2.60-2.76 (m, 2H),
3.07-3.25 (m, 4H), 3.48-3.60 (m, 2H), 3.64 (s, 4H), 3.67 (s,
2H), 3.71 (s, 2H), 3.75 (s, 2H), 3.90, 3.91 (ss, 9H), 7.14-7.70
(m, 13H), 7.84-8.08 (m, 6H); 13C NMR (CDCl3) δ 21.5, 31.3,
45.6, 46.8, 52.1, 52.8, 57.9, 58.7, 59.7, 60.3, 121.1, 121.4, 127.0,
128.4, 129.7, 130.0, 130.2, 133.4. 133.5, 136.8, 137.1, 139.5,
143.2, 158.3, 158.9, 167.1; MS (ESI) m/ z 837 (M + 1)+; HRMS
(FAB) m/ z 837.356 (M + 1)+ (C46H52N4SO9 requires 837.353).
3-[[2-[[3-(Met h oxyca r b on yl)b en zyl][[6-[[b is[(3-m et h -
oxyca r b on yl)b en zyl]a m in o]m et h yl]-2-p yr id in yl]m et h -
yl]a m in o]eth yl]tosyla m in o]-1-p r op yl Aceta te (28). Acetyl
chloride (0.5 mL) was added dropwise to a stirred solution of
6 (40 mg, 47 µmol) and Et3N (0.5 mL) in 5 mL of CHCl3. The
resulting reaction mixture was stirred at rt for 1 h and diluted
with CHCl3 (50 mL). The CHCl3 solution was washed three
times with aqueous NaHCO3 and once with brine. The dried
(Na2SO4) organic phase was concentrated under reduced
pressure, and the residue was purified by flash chromatogra-
phy on a silica gel column. Elution with 2:1 hexanes-EtOAc
and then 100% EtOAc afforded 40 mg (95%) of acetate product
28 as a pale yellow oil: silica gel TLC Rf 0.42 (1:1 hexanes-
ethyl acetate); 1H NMR (CDCl3) δ 1.55-1.70 (m, 2H), 1.94 (s,
2H), 2.37 (s, 3H), 2.60-2.73 (m, 2H), 2.99-3.10 (m, 2H), 3.13-
3.25 (m, 2H), 3.25-3.40 (m, 2H), 3.64 (s, 4H), 3.67(s, 2H), 3.71
(s, 2H), 3.76 (s, 2H), 3.90, 3.91 (ss, 9H), 7.20 (d, 2H, J ) 8.3
Hz), 7.30-7.70 (m, 9H), 7.85-8.10 (m, 6H); MS (FAB) m/ z
879 (M + H)+; HRMS (FAB) m/ z 1011.258 (M + Cs)+
(C48H54N4SO10Cs requires 1011.261).
2-(Br om om eth yl)-6-(p h th a lim id om eth yl)p yr id in e (31).
A mixture of 2,6-bis(bromomethyl)pyridine (29) (10.0 g, 37.7
mmol), potassium phthalimide (30) (7.69 g, 41.5 mmol, 1.1
equiv), and anhydrous K2CO3 (15.6 g, 113.2 mmol, 3.0 equiv)
in 480 mL of anhydrous CH3CN was heated at reflux for 24 h.
The solvent was evaporated, and the residue was dissolved in
400 mL of H2O. The mixture was extracted with CH2Cl2 (2 ×
400 mL). The combined organic phase was washed with brine,
dried (Na2SO4), and concentrated under reduced pressure. The
residue was purified by flash chromatography on a silica gel
column. Elution with 7:3 and then 4:6 hexanes-EtOAc gave
4.82 g (39%) of product 31 as white crystals: mp 137-138 °C;
silica gel TLC Rf 0.52 (4:6 hexanes-EtOAc); 1H NMR (CDCl3,
400 MHz) δ 4.47 (s, 2H), 5.00 (s, 2H), 7.14 (d, 1H, J ) 7.6 Hz),
7.34 (d, 1H, J ) 7.6 Hz), 7.64 (t, 1H, J ) 7.6 Hz), 7.74-7.77
(m, 2H), 7.89-7.91 (m, 2H); 13C NMR (CDCl3) δ 33.7, 42.8,
120.3, 122.2, 123.5, 132.2, 134.1, 137.7, 155.2, 156.6, 168.1;
147.9, 156.4; HRMS (FAB) m/ z 536.046 (M
+
Cs)+
(C16H25N3O7SCs requires 536.045). Anal. Calcd for
C16H25N3O7S: C, 47.63; H, 6.25; N, 10.41. Found: C, 47.84;
H, 6.40; N, 10.21.
3-[[2-[(2-Nitr oben zen esu lfon yl)[[6-(ph th alim idom eth yl)-
2-p yr id in yl]m e t h yl]a m in o]e t h yl](t er t -b u t oxyca r b on -
yl)a m in o]-1-p r op a n ol (7). A mixture of 35 (16.4 g, 40.8
mmol), 31 (14.9 g, 45.0 mmol, 1.1 equiv), and anhydrous K2CO3
(39.5 g, 285 mmol) in 100 mL of anhydrous DMF was stirred
at rt under an Ar atmosphere for 24 h. The solvent was
evaporated under reduced pressure. The residue was dissolved
in H2O (200 mL), and the mixture was extracted with CH2Cl2
(2 × 200 mL). The combined organic phase was washed with
brine, dried (Na2SO4), and concentrated. The residue was
purified by flash chromatography on a silica gel column.
Elution with 6:1 hexanes-EtOAc and then 100% EtOAc
afforded 23.5 g (88%) of the orthogonally protected product 7
as a white foam: silica gel TLC Rf 0.42 (100% EtOAc); 1H NMR
(CDCl3, 400 MHz) δ 1.38 (s, 9H), 1.54-1.57 (m, 2H), 3.16-
3.18 (m, 4H), 3.43-3.47 (m, 4H), 3.62 (br, 1H, ex D2O), 4.59
(s, 2H), 4.89 (s, 2H), 7.17-7.23 (m, 3H), 7.56-7.64 (m, 4H),
7.75-7.78 (m, 2H), 7.87-7.89 (m, 2H); 13C NMR (CDCl3) δ
28.2, 30.3, 42.5, 42.7, 45.1, 46.5, 52.8, 58.1, 80.6, 120.3, 121.2,
123.4, 124.0, 125.2, 128.1, 128.9, 130.4, 131.6, 132.0, 133.3,
133.4, 134.2, 137.6, 147.8, 155.0, 154.5, 156.4, 167.9; HRMS
(FAB) m/ z 786.122 (M + Cs)+ (C31H35N5O9SCs requires
786.121).
3-[[2-[(2-Nit r ob en zen esu lfon yl)[[6-(a m in om et h yl)-2-
pyr idin yl]m eth yl]am in o]eth yl](ter t-bu toxycar bon yl)am i-
n o]-1-p r op a n ol (8). A solution of 7 (9.94 g, 15.2 mmol) in
100 mL of CH2Cl2 under an Ar atmosphere was cooled to 0
°C, and hydrazine (3.50 mL, 65.8 mmol, 4.3 equiv) was added
slowly. The resulting reaction mixture was stirred at rt for

Pyridinopolyamine Libraries
J . Org. Chem., Vol. 62, No. 15, 1997 5163
24 h and then treated with H2O (200 mL). The mixture was
extracted with CH2Cl2 (2 × 200 mL). The combined organic
phase was washed with brine, dried (Na2SO4), and concen-
trated. The residue was purified by flash chromatography on
a silica gel column. Elution with 9:1 and then 1:4 EtOAc-
MeOH afforded 6.13 g (77%) of diprotected product 8 as a pale
yellow thick oil: silica gel TLC Rf 0.45 (100:1 MeOH-30%
in anhydrous CH3CN was stirred at rt for 23 h. The solvent
was evaporated under reduced pressure, and the residue was
dissolved in H2O-CHCl3. The layers were separated, and the
aqueous layer was extracted with CHCl3. The combined
organic phase was dried (Na2SO4), and the solvent was
evaporated. The residue was purified by preparative thin
layer chromatography (PLC) affording the desired library.
Libr a r y 38: colorless oil, yield 160 mg (53%), silica gel TLC
Rf 0.36-0.54 (20:1 EtOAc-MeOH); 1H NMR (CDCl3) δ 1.55-
1.70 (m, 2H), 2.25 (s, 2.25H), 2.30 (s, 2.25H), 2.34 (s, 3H), 2.47-
2.68 (m, 6H), 3.38-3.74 (m, 14H), 3.89 (s, 2.25H), 3.92 (s,
2.25H), 6.91-7.25 (m, 10H), 7.28-7.68 (m, 6H), 7.84-8.10 (m,
3H); MS (ESI) m/ z 655, 699, 743, 787 (M + 1)+; 677, 721, 765,
809 (M + Na)+.
1
NH4OH); H NMR (DMSO-d6, D2O, 400 MHz) δ 1.31 (s, 9H),
1.41-1.55 (m, 2H), 2.93-3.05 (m, 2H), 3.23-3.30 (m, 2H),
3.31-3.33 (m, 2H), 3.39-3.43 (m, 2H), 3.62 (s, 2H), 4.63 (s,
2H), 7.09-7.11 (d, 1H, J ) 7.6 Hz), 7.28-7.30 (d, 1H, J ) 7.6
Hz), 7.65-7.69 (t, 1H, J ) 7.6 Hz), 7.74-7.76 (m, 1H), 7.84-
7.86 (m, 1H), 7.92-7.95 (m, 1H), 7.95-8.02 (m, 1H); 13C NMR
(DMSO-d6) δ 27.9, 31.0, 44.1, 45.1, 46.3, 47.1, 52.4, 58.3, 78.8,
119.8, 119.9, 124.2, 130.0, 132.3, 134.3, 137.3, 147.5, 154.3,
Libr a r y 39: pale yellow oil, yield 0.25 g (88%), silica gel
+
Cs)+
1
154.5, 162.6; HRMS (FAB) m/ z 656.116 (M
TLC Rf 0.40-0.58 (20:1 EtOAc-MeOH); H NMR (CDCl3) δ
(C23H33N5O7SCs requires 656.115). Anal. Calcd for
C23H33N5O7S: C, 52.76; H, 6.35. Found: C, 52.41; H, 6.16.
3-[[2-[[[6-(Am in om et h yl)-2-p yr id in yl]m et h yl]a m in o]-
eth yl](ter t-bu toxyca r bon yl)a m in o]-1-p r op a n ol (1). Thio-
phenol (185 µL, 199 mg, 1.8 mmol) was added to a stirred
mixture of 8 (0.53 g, 1.0 mmol) and anhydrous K2CO3 (1.0 g,
7.2 mmol) in anhydrous DMF (20 mL). The resulting reaction
mixture was stirred at rt for 3 h and concentrated under
vacuum to remove the solvent. The residue was dissolved in
a mixture of H2O and CHCl3, and the pH was adjusted to 13-
14. The organic phase was separated, and the aqueous phase
was extracted with CHCl3. The combined organic phase was
washed with brine, dried (Na2SO4), and concentrated under
reduced pressure. The residue was purified by flash chroma-
tography on a silica gel column. Elution with 100% MeOH
and then 50:1 MeOH-30% NH4OH afforded 250 mg (74%) of
the title compound 1 as a pale yellow oil. The compound 1
obtained by this procedure (Scheme 3) shows identical chro-
matographic and spectroscopic properties to those of the same
compound synthesized by another route (Scheme 1).
P r ep a r a tion of Libr a r y 36. A solution of R-bromo-m-
xylene (0.494 g, 2.66 mmol, 2 equiv) and methyl 3-(bromom-
ethyl)benzoate (0.61 g, 2.66 mmol, 2 equiv) in 25 mL of
anhydrous CH3CN was added dropwise at rt to a stirred
mixture of 1 (0.45 g, 1.33 mmol) and anhydrous K2CO3 (2.67
g, 19.3 mmol) in 40 mL of anhydrous CH3CN. The resulting
reaction mixture was stirred at rt overnight. After the solvent
was evaporated, the residue was dissolved in H2O and CHCl3.
The layers were separated, and the aqueous layer was
extracted with CHCl3. The combined organic phase was
washed with brine and dried (Na2SO4). The solvent was
evaporated, and the residue was purified by flash chromatog-
raphy on a silica gel column. Elution with 10:1 hexanes-
EtOAc and then 100% EtOAc afforded 0.88 g (93%) of the
intermediate library 36 as a pale yellow oil: silica gel TLC Rf
0.31, 0.42, 0.54 and 0.62 (1:2 hexanes-EtOAc); 1H NMR
(CDCl3) δ 1.26 (s, 9H), 1.40-1.60 (m, 2H), 2.32 (s, 2.25H), 2.34
(s, 2.25H), 2.57-2.68 (m, 2H), 3.15-3.35 (m, 4H), 3.40-3.52
(m, 2H), 3.55-3.78 (m, 10H), 3.91 (s, 2.25H), 3.92 (s, 2.25H),
6.98-7.08 (m, 2H), 7.10-7.24 (m, 4H), 7.30-7.72 (m, 6H), 7.85-
8.10 (m, 3H); MS (ESI) m/ z 651, 695, 739, 783 (M + H)+; 673,
717, 761, 805 (M + Na)+.
1.55-1.70 (m, 2H), 2.29 (s, 2.25H), 2.33 (s, 2.25H), 2.47-2.68
(m, 6H), 3.44-3.72 (m, 14H), 3.88 (s, 3H), 3.89 (s, 2.25H), 3.91
(s, 2.25H), 6.97-7.22 (m, 7H), 7.28-7.68 (m, 7H), 7.78-8.08
(m, 5H); MS (ESI) m/ z 699, 743, 787, 831 (M + 1)+; 721, 765,
809, 853 (M + Na)+.
Libr a r y 9. This library was prepared as above for 36 from
1 (560 mg, 1.65 mmol), anhydrous K2CO3 (3.5 g, 25.0 mmol),
and a solution of benzyl bromide (123 µL, 171 mg, 1.0 mmol),
3-fluorobenzyl bromide (124 µL, 189 mg, 1.0 mmol), R-bromo-
m-xylene (141 µL, 185 mg, 1.0 mmol), methyl 3-(bromometh-
yl)benzoate (229 mg, 1.0 mmol), 3-nitrobenzyl bromide (216
mg, 1.0 mmol) and R′-bromo-R,R,R-trifluoro-m-xylene (155 µL,
239 mg, 1.0 mmol) in 90 mL of anhydrous CH3CN. Library 9
was obtained as a pale yellow oil: yield 0.89 g (76%); silica
gel TLC Rf 0.30-0.70 (1:2 hexanes-EtOAc); 1H NMR (CDCl3)
δ 1.27 (s, 9H), 1.40-1.70 (m, 2H), 2.32 (s, 0.75H), 2.34 (s,
0.75H), 2.47-2.72 (m, 2H), 3.15-3.35 (m, 4H), 3.38-3.52 (m,
2H), 3.54-3.80 (m, 12H), 3.91 (s, 0.75H), 3.92 (s, 0.75H), 6.90-
8.32 (m, 15.2H); MS (ESI) m/ z 609-813 (M + 1)+.
Libr a r y 10. This library was prepared as above for 9 from
six benzylic bromides (0.2 mmol each), 2 (130 mg, 0.33 mmol),
and anhydrous K2CO3 (0.80 g, 5.7 mmol) in 20 mL of
anhydrous CH3CN. Library 10 was obtained as a pale yellow
oil: yield 180 mg (71%); silica gel TLC Rf 0.30-0.70 (1:4
1
hexanes-EtOAc); H NMR (CDCl3) δ 1.27 (s, 9H), 1.41-1.62
(m, 2H), 2.32 (s, 0.75H), 2.34 (s, 0.75H), 2.38 (s, 3H), 2.58-
2.80 (m, 2H), 3.04-3.28 (m, 4H), 3.50-3.85 (m, 12H), 3.91 (s,
0.75H), 3.92 (s, 0.75H), 6.85-8.30 (m, 19.2H); MS (ESI) m/ z
663-867 (M + 1)+
.
Libr a r y 11. This library was synthesized as above for
library 37 from 0.77 g (1.08 mmol) of library 9 and 8 mL of
TFA. Library 11 was obtained as a pale yellow oil: yield 0.63
g (95%); silica gel TLC Rf 0.36-0.50 (100:1 MeOH-30%
NH4OH); 1H NMR (CDCl3) δ 1.49-1.68 (m, 2H), 2.32 (s,
0.75H), 2.34 (s, 0.75H), 2.53-2.76 (m, 6H), 3.50-3.80 (m, 14H),
3.90 (s, 0.75H), 3.92 (s, 0.75H), 6.85-8.30 (m, 15.2H); MS (ESI)
m/ z 509-713 (M + 1)+.
Libr a r y 12: colorless oil, yield 71 mg (70%), silica gel TLC
Rf 0.30-0.45 (20:1 EtOAc-MeOH); 1H NMR (CDCl3) δ 1.60-
1.76 (m, 2H), 2.31 (s, 0.75H), 2.33 (s, 0.75H), 2.48-2.73 (m,
6H), 3.42-3.80 (m, 14H), 3.89 (s, 0.75H), 3.91 (s, 0.75H), 6.85-
8.30 (m, 20.2H); MS (ESI) m/ z 656-860 (M + 1)+.
P r ep a r a tion of Libr a r y 37. CF3COOH (8 mL) was added
to a flask containing library 36 (0.75 g, 1.04 mmol) at 0 °C.
The resulting solution was stirred at rt for 3 h. TFA was
evaporated under reduced pressure, and the residue was
dissolved in 200 mL of chloroform. The solution was washed
Libr a r y 13: pale yellow oil, yield 55 mg (78%), silica gel
1
TLC Rf 0.25-0.50 (20:1 EtOAc-MeOH); H NMR (CDCl3) δ
1.55-1.72 (m, 2H), 2.25 (s, 3H), 2.30 (s, 0.75H), 2.34 (s, 0.75H),
2.49-2.70 (m, 6H), 3.45 (s, 2H), 3.49-3.78 (m, 14H), 3.89 (s,
0.75H), 3.92(s, 0.75H), 6.85-8.30 (m, 19.2H); MS (ESI) m/ z
613-817 (M + 1)+.
three times with
a saturated K2CO3 solution and dried
(Na2SO4). The solvent was evaporated, and the residue was
purified by flash chromatography on a silica gel column.
Elution with 100% methanol and then 100:1 MeOH-30%
NH4OH afforded 0.50 g (78%) of library 37 as a pale yellow
oil: silica gel TLC Rf 0.43 (100:1 MeOH-30% NH4OH); 1H
NMR (CDCl3) δ 1.52-1.67 (m, 2H), 2.32 (s, 2.25H), 2.34 (s,
2.25H), 2.56-2.68 (m, 6H), 3.54-3.78 (m, 12H), 3.90 (s, 2.25H),
3.92 (s, 2.25H), 6.98-7.23 (m, 6H), 7.27-7.70 (m, 6H), 7.86-
8.09 (m, 3H); MS (ESI) m/ z 551, 595, 639, 683 (M + 1)+.
Gen er a l P r oced u r e for th e P r ep a r a tion of Libr a r ies
38, 39, a n d 12-21. A mixture of selected benzylic bromide
(1.4 equiv), library 37 or 11 (1.0 equiv), and K2CO3 (15 equiv)
Libr a r y 14: colorless oil, yield 45 mg (45%), silica gel TLC
Rf 0.43-0.60 (40:1 EtOAc-MeOH); 1H NMR (CDCl3) δ 1.55-
1.75 (m, 2H), 2.32 (s, 0.75H), 2.34 (s, 0.75H), 2.47-2.75 (m,
6H), 3.40-3.80 (m, 14H), 3.90 (s, 0.75H), 3.92 (s, 0.75H), 6.80-
8.30 (m, 19.2H); MS (ESI) m/ z 616-820 (M + 1)+.
Libr a r y 15: pale yellow oil, yield 45 mg (41%), silica gel
1
TLC Rf 0.47-0.68 (50:1 EtOAc-MeOH); H NMR (CDCl3) δ
1.55-1.74 (m, 2H), 2.31 (s, 0.75H), 2.33 (s, 0.75H), 2.48-2.72
(m, 6H), 3.45-3.80 (m, 14H), 3.90 (s, 0.75H), 3.92 (s, 0.75H),
6.80-8.30 (m, 19.2H); MS (ESI) m/ z 643-847 (M + 1)+.
Libr a r y 16: colorless oil, yield 60 mg (49%), silica gel TLC
Rf 0.37-0.57 (40:1 EtOAc-MeOH); 1H NMR (CDCl3) δ 1.57-

5164 J . Org. Chem., Vol. 62, No. 15, 1997
An et al.
1
1.75 (m, 2H), 2.31 (s, 0.75H), 2.33 (s, 0.75H), 2.48-2.73 (m,
6H), 3.42-3.80 (m, 14H), 3.89 (s, 3.75H), 3.91 (s, 0.75H), 6.85-
8.30 (m, 19.2H); MS (ESI) m/ z 656-860 (M + 1)+.
gel TLC Rf 0.15-0.46 (2:1 EtOAc-MeOH); H NMR (CDCl3)
δ 1.50-1.76 (m, 2H), 2.30 (s, 0.75H), 2.34 (s, 0.75H), 2.55-
2.82 (m, 6H), 3.09 (s, 3H), 3.37 (s, 2H), 3.48-3.80 (m, 17H),
3.90 (s, 0.75H), 3.92 (s, 0.75H), 6.85-8.32 (m, 15.2H); MS (ESI)
m/ z 610-814 (M + 1)+.
Libr a r y 17: pale yellow oil, yield 75 mg (71%), silica gel
1
TLC Rf 0.55-0.73 (50:1 EtOAc-MeOH); H NMR (CDCl3) δ
1.47-1.78 (m, 2H), 2.32 (s, 0.75H), 2.34 (s, 0.75H), 2.48-2.85
(m, 6H), 3.45-3.80 (m, 14H), 3.90 (s, 0.75H), 3.92 (s, 0.75H),
6.80-8.30 (m, 19.2H); MS (ESI) m/ z 666-870 (M + 1)+.
Libr a r y 18: pale yellow oil, yield 45 mg (65%), silica gel
Ack n ow led gm en t. The authors thank Dr. Rich H.
Griffey for his working on mass spectrum simulation
of library 15, Dr. Susan M. Freiser for helpful discussion
on the complexity of libraries, Mrs. Lisa M. Risen, Laura
Wilson-Lingardo, and Dr. J acqueline R. Wyatt for
antibacterial screening, and Dr. Ramesh Bharadwaj for
his help on the synthesis of compound 22. High-
resolution (FAB and EI) and electrospray ionization
mass spectrometry were provided by The Scripps Re-
search Institute Mass Spectrometry.
1
TLC Rf 0.39-0.56 (20:1 EtOAc-MeOH); H NMR (CDCl3) δ
1.50-1.68 (m, 2H), 2.31 (s, 0.75H), 2.34 (s, 0.75H), 2.56-2.80
(m, 6H), 3.25 (s, 2H), 3.52-3.80 (m, 17H), 3.90 (s, 0.75H), 3.92
(s, 0.75H), 6.85-8.30 (m, 15.2H); MS (ESI) m/ z 581-785 (M
+ 1)+.
Libr a r y 19: pale yellow oil, yield 37 mg (58%), silica gel
1
TLC Rf 0.48-0.69 (40:1 EtOAc-MeOH); H NMR (CDCl3) δ
1.57-1.74 (m, 2H), 2.30 (s, 0.75H), 2.34 (s, 0.75H), 2.56-2.80
(m, 6H), 3.38-3.82 (m, 16H), 3.91 (s, 0.75H), 3.93 (s, 0.75H),
6.85-8.30 (m, 15.2H); MS (ESI) m/ z 548-752 (M + 1)+.
Libr a r y 20: pale yellow thick oil, yield 35 mg (53%), silica
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
spectra of compounds 1-8, 23, and 34; 1H NMR spectrum,
electrospray MS, computer-simulated MS, and theorectical
molecular masses of library 15 (28 pages). This material is
contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
1
gel TLC Rf 0.35-0.60 (3:1 EtOAc-MeOH); H NMR (CDCl3)
δ 1.50-1.70 (m, 2H), 2.30 (s, 0.75H), 2.34 (s, 0.75H), 2.42-
2.70 (m, 6H), 3.04 (s, 2H), 3.52-3.85 (m, 14H), 3.90 (s, 0.75H),
3.92 (s, 0.75H), 5.38-5.68 (bs, 2H), 6.85-8.32 (m, 15.2H); MS
(ESI) m/ z 566-770 (M + 1)+.
Libr a r y 21. This library was prepared according to general
procedure by stirring the reaction mixture at 50-60 °C for 24
h and obtained as a pale yellow oil: yield 42 mg (59%); silica
J O970535J