First total synthesis of phenylpyridine analogues of the antimitotic rhazinilam

Article abstract of DOI:10.1021/jo0014156

The first synthesis of phenylpyridine analogues of rhazinilam and evaluation of these new structures as inhibitors of microtubule disassembly by interaction with tubulin are described. The synthesis is based on such key steps as picolinic metalation, hete

Full text of DOI:10.1021/jo0014156

2654
J . Org. Chem. 2001, 66, 2654-2661
F ir st Tota l Syn th esis of P h en ylp yr id in e An a logu es of th e
An tim itotic Rh a zin ila m
Eric Pasquinet,† Patrick Rocca,*,† Se´bastien Richalot,† Franc¸oise Gue´ritte,‡ Daniel Gue´nard,‡
Alain Godard,† Francis Marsais,† and Guy Que´guiner†
Institut de Recherche en Chimie Organique Fine, UMR 6014, Institut National des Sciences Applique´es,
B.P. 08, 76131 Mont Saint Aignan Cedex, France, and Institut de Chimie des Substances Naturelles,
CNRS, Avenue de la Terrasse, Baˆt. 27, 91198 Gif-sur-Yvette Cedex, France
Patrick.Rocca@insa-rouen.fr
Received September 25, 2000
The first synthesis of phenylpyridine analogues of rhazinilam and evaluation of these new structures
as inhibitors of microtubule disassembly by interaction with tubulin are described. The synthesis
is based on such key steps as picolinic metalation, hetero-ring cross-coupling and reduction of an
acetyl group to an ethyl group. Elaboration of a quaternary picolinic carbon is one of the challenges
of the synthesis. Biological evaluation of compounds bearing a quaternary picolinic carbon showed
interactions with tubulin similar to (-)-rhazinilam but at a lower level.
In tr od u ction
(-)-Rhazinilam 1 (Figure 1) is an axially chiral phe-
nylpyrrole compound which has been isolated from
various Apocynaceae species.1-3 Biological studies showed
that rhazinilam exhibited the same behavior as paclitaxel
(Taxol) on mammalian cells.4 It induces both microtubule
bundling in interphase and blocks mitotic cells in aster-
like structures. In vitro, this antimitotic compound
induces spiralization of tubulin (vinblastine effect) and
inhibits the cold-induced disassembly of microtubules
(paclitaxel effect). The naturally occurring (-)-rhazinilam
1 is found as a sole enantiomer, and it should be noted
that the nonnatural enantiomer is inactive.2 Structurally,
the dihedral angle characterizing the phenylpyrrolic
linkage of 1 is 95°, and the amide conformation is cis.5
Despite its biological interest, (-)-rhazinilam 1 suffers
from lack of activity in vivo. This prompted synthetic
chemists to prepare structural analogues of 1. Thus, a
number of phenylpyrroles 2 were obtained, by total
synthesis,6 biosynthetic-like schemes7-10 or modification7
of 1. Recently, the team of Franc¸oise Gue´ritte and Daniel
F igu r e 1.
Gue´nard focused on the synthesis of biphenyls11
3
mimicking the structure of (-)-rhazinilam and studied
the replacement of the lactam moiety by a lactone, urea,
or best, by a carbamate group.12 These biphenyl com-
pounds showed an activity on microtubule disassembly
very close to that of (-)-rhazinilam, and carbamate (-)-4
was even twice as active as 1.11,12 This work established
the first features needed for maximum antitubulin activ-
ity. Thus, the presence of a biaryl unit sustaining a nine-
membered ring is crucial, as well as a quaternary center
at the 13 position, mimicking the stereogenic carbon of
1. Moreover, only one atropoisomer retains the activity
of a racemate.
† Institut de Recherche en Chimie Organique Fine.
‡ Institut de Chimie des Substances Naturelles.
(1) Linde, H. H. A. Helv. Chim. Acta 1965, 48, 1822.
(2) Thoison, O.; Gue´nard, D.; Se´venet, T.; Kan-Fan, C.; Quirion, J .-
C.; Husson, H.-P.; Deverre, J .-R.; Chan, K.-C.; Potier, P. C. R. Acad.
Sc. Paris 1987, 304, Se´rie II, 157.
(3) Goh, S. H.; Razak Mohd Ali, A.; Wong, W. H. Tetrahedron 1989,
45, 7899.
(4) David, B.; Se´venet, T.; Morgat, M.; Gue´nard, D.; Moisand, A.;
Tollon, Y.; Thoison, O.; Wright, M. Cell Motil. Cytoskeleton 1994, 28,
317.
(5) Abraham, D. J .; Rosenstein, R. D.; Lyon, R. L.; Fong, H. H. S.
Tetrahedron Lett. 1972, 10, 909.
(6) Alazard, J .-P.; Millet-Paillusson, C.; Boye´, O.; Gue´nard, D.;
Chiaroni, A.; Riche, C.; Thal, C. Bioorg. Med. Chem. Lett. 1991, 1, 725-
728. (b) Alazard, J .-P.; Millet-Paillusson, C.; Gue´nard, D.; Thal, C. Bull.
Soc. Chim. Fr. 1996, 133, 251.
(7) David, B.; Se´ve´net, T.; Thoison, O.; Awang, K.; Pa¨ıs, M.; Wright,
M.; Gue´nard, D. Bioorg. Med. Chem. Lett. 1997, 7, 2155.
(8) Dupont, C.; Gue´nard, D.; Tchertanov, L.; Thoret, S.; Gue´ritte,
F. Bioorg. Med. Chem. Lett. 1999, 7, 22961.
As part of the studies in this series, we considered the
synthesis of phenylpyridine analogues 5 and 6. This
choice was confirmed by molecular modeling studies
showing that compounds 5 and 6 fitted well the confor-
(9) Le´vy, J .; Soufyane, M.; Mirand, C.; Do¨e´ de Maindreville, M.;
Royer, D. Tetrahedron Asymmetry 1997, 8, 4127.
(10) Soufyane, M. Ph. D. Universite´ de Reims Champagne-Ardenne,
France, 1993.
(11) Pascal, C.; Dubois, J .; Gue´nard, D.; Gue´ritte, F. J . Org. Chem.
1998, 63, 6414.
(12) Pascal, C.; Dubois, J .; Gue´nard, D.; Tchertanov, L.; Thoret, S.;
Gue´ritte, F. Tetrahedron 1998, 54, 14737.
10.1021/jo0014156 CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/22/2001

Phenylpyridine Analogues of Rhazinilam
J . Org. Chem., Vol. 66, No. 8, 2001 2655
Sch em e 1
Sch em e 3a
a
(i) Tf2O, pyridine, 20 °C, 75 min. (ii) 1.3 equiv of 2-pivaloy-
laminophenylboronic acid, Pd(PPh3)4, K2CO3 2 M, toluene, EtOH,
6 h reflux (N2). (iii) Tf2O, pyridine, 20 °C, 45 min; then 1.2 equiv
of 2-pivaloylaminophenylboronic acid, Pd(PPh3)4, K2CO3 2 M,
toluene, EtOH, 80 °C, 3 h (N2).
Sch em e 2
ridine 7 was used as starting material to synthesize
biaryl 9. Treatment of 7 with triflic anhydride in pyri-
dine15 at room temperature led to the corresponding
triflate 8 in a 73% yield. A cross-coupling reaction, using
Suzuki conditions,14 was then carried out between triflate
8 and 2-pivaloylaminophenylboronic acid16 to afford bi-
aryl 9 in very good yield. However, a better synthesis of
9 was designed by using a “one-pot” procedure, thus
avoiding the tedious isolation of triflate 8 (Scheme 3).
The next step of the work consisted in introducing the
desired alkyl chains at the picolinic position. Thus,
treatment of 9 with n-BuLi at low temperature followed
by quenching with ethyl iodide yielded 75% of propyl
product 10, together with a small amount of pentyl
derivative 11. Compound 12 was obtained similarly in
good yield, after metalation of 10 by using the superbasic
mixture n-BuLi/t-BuOK/diisopropylamine (“KDA”).13,17-18
It should be noted that 3-3.5 equiv of base were needed
in each case for complete deprotonation (Scheme 4).
To introduce the future carbon chain of the lactam ring,
we considered the reaction of alkylpyridines 9, 10, and
12 with 4-bromobutene.13 Compounds 9 and 10 were thus
successfully metalated by n-BuLi and afforded the cor-
responding alkenes 13 in good yields (Scheme 5). How-
ever, the more hindered compound 12 was found to be
inert toward metalation with strongly basic agents, even
when treated by the superbasic KDA. Whatever the
conditions used, the characteristic deep red color of
picolinic anions could not be observed. The same unsuc-
cessful results were obtained with the parent compound
bearing an isopropyl moiety at the 2-position. Direct
quaternization of the picolinic carbon, a successful pro-
cess on 2-isopropylpyridine19 and even more hindered
alkylpyridines,13 was therefore not applicable to our
compounds arylated at the 3-position.
mation of 1. Previously, we reported synthetic method-
ologies toward simple pyridinic models bearing a qua-
ternary picolinic carbon.13 Here, we wish to report the
first total synthesis of phenylpyridine analogues 5 and
6 of rhazinilam, their antitubulin activity, and discuss
interesting features of some atropoisomeric structures
encountered during this work (Figure 1).
Retr osyn th esis
A retrosynthetic analysis suggests that phenylpyridine
analogues 5 could be prepared by cyclization of amino
acid A. The latter could be obtained from key compound
B, using a previously described route13 mainly consisting
of dialkylation and cyanoethylation. Biaryl B would arise
from a cross-coupling reaction14 between the required
benzene and pyridine building blocks (Scheme 1).
Our approach is based on installing the biaryl unit
early in the synthesis, followed by elaboration of the
quaternary picolinic carbon. Indeed, Gue´ritte et al.
showed the sensitivity of cross-coupling toward steric
hindrance in biphenyl series.11 Concerning carbamate 6,
our retrosynthetic approach is quite similar, as outlined
in Scheme 2.
Nevertheless, we were still able to carry out the quick
total synthesis of C-13 secondary and tertiary analogues
of rhazinilam. Thus, oxidative cleavage of the double bond
of compounds 13 by potassium permanganate in weekly
acidic medium20 led to the hard-to-extract corresponding
Resu lts a n d Discu ssion
(15) Draper, T. L.; Bailey, T. R. Synlett 1995, 157.
(16) Rocca, P.; Marsais, F.; Godard, A.; Que´guiner, G. Tetrahedron
1993, 49, 49.
(17) Raucher, S.; Koolpe, G. A. J . Org. Chem. 1978, 43, 3794.
(18) Margot, C.; Schlosser, M. Tetrahedron Lett. 1985, 26, 1035.
(19) Pasquinet, E.; Rocca, P.; Godard, A.; Marsais, F.; Que´guiner,
G. Tetrahedron 1998, 54, 8771.
Analogues with a secondary and tertiary picolinic
carbon. Commercially available 3-hydroxy-2-methylpy-
(13) Pasquinet, E.; Rocca, P.; Godard, A.; Marsais, F.; Que´guiner,
G. J . Chem. Soc., Perkin Trans. 1 1998, 3807.
(14) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(20) Krapcho, A. P.; Larson, J . R.; Eldridge, J . M. J . Org. Chem.
1977, 42, 3749.

2656 J . Org. Chem., Vol. 66, No. 8, 2001
Pasquinet et al.
Sch em e 4a
linkage is not restricted enough (the signals would then
be found at a weighted average value for the two
conformers), or there is only indeed one diastereoisomer,
the other one being disfavored on steric consider-
ations.11,23
An a logu es w ith a Qu a ter n a r y P icolin ic Ca r bon .
Treatment of 9 with n-BuLi at low temperature followed
by action of dimethylacetamide13,24 led to the correspond-
ing pyridylacetone 16 with a good conversion factor (7%
of unreacted starting material remained and was insepa-
rable from the product). Compound 16 was isolated as a
mixture of tautomers, as expected from previous work24-27
with the ketone 16A/enol 16B ratio being 9:1 in CDCl3.
Action of 1 equiv of n-BuLi on 16, followed by alkylation,
afforded compounds 17 in good yields (Scheme 6). These
conditions avoided dialkylation, except for methylation
with methyl iodide. Quaternization of the picolinic carbon
and introduction of the desired cyanoethyl moiety were
best achieved by treatment of ketones 17 with acryloni-
trile in the presence of benzyltrimethylammonium hy-
droxide28 to give derivatives 18. In the case of 17b (R )
Et), reactivity was low at the picolinic carbon, and
tricyanoethylated compound 19 was obtained as a byprod-
uct. Interestingly, the wanted Michael-adduct 18b was
not protonated by HCl on the pyridinic nitrogen, which
allowed an easy separation of 18b and recovery of
starting ketone 17b (Scheme 6).
a
(i) (1) 3.1 equiv of n-BuLi, THF, -20 °C, 1 h; (2) EtI, -50 °C,
30 min. (ii) 1) 3.5 equiv of KDA, THF, -50 °C, 30 min; (2) EtI,
-70 °C, 15 min.
Atr op isom er ic P h en om en on . Compounds 18 have
bulky substituents in the ortho-position, thus inducing
a restricted rotation around the biaryl bond. Since these
compounds possess already a stereogenic picolinic carbon,
two diastereoisomers are expected. This phenomenon was
Sch em e 5a
1
observed by H NMR analysis where most of the spectra
were doubled. We particularly studied the behavior of
18a and 18b in solution, where the two diastereoisomers
were found to be in thermodynamic equilibrium, due to
slow rotation around the biaryl bond. We were able to
isolate the major isomer by precipitation from a mixture
of ethyl acetate and light petroleum. The 1H NMR
spectrum of the freshly dissolved solid showed only a
single set of signals, whereas that of the mother liquor
exhibited the two types of signals previously observed.
Conversion of this pure diastereoisomer to the thermo-
dynamic mixture was monitored by 1H NMR and was
found to be much faster in DMSO-d6 than in CDCl3. At
higher temperature, the interconversion rate was in-
creased markedly (Table 1). The diastereoisomeric ratios
at equilibrium were about the same for the two products,
i.e., ca. 3:1 in CDCl3 and ca. 2:1 in DMSO.
These experiments allowed us to calculate the rotation
barriers29 at 25 °C in CDCl3: 22.6 and 23.7 kcal/mol,
a
(i) (R ) H) 1) 3.1 equiv of n-BuLi, THF, -20 °C, 1 h; (2)
4-bromobutene, -50 °C f 0 °C, 1 h. (R) Et) (1) 3.5 equiv equiv
KDA, -50 °C, 30 min; (2) 4-bromobutene, -40 °C, 40 min. (ii)
KMnO4, AcOH, H2O, 20 °C, 1 h (R ) H) or 5h (R ) Et). (iii) H2SO4
30%, 160 °C, 2h then NH4OH 25%. (iv) HOBT, EDCI, NEt3,
CH2Cl2, 40 °C/24 h (R ) H) or 20 °C/48 h (R ) Et).
(21) Patel, D. V.; VanMiddlesworth, F.; Donaubauer, J .; Gannett,
P.; Sih, C. J . J . Am. Chem. Soc. 1986, 108, 4603.
(22) Carlsen, P. H. J .; Katsuki, T.; Martin, V. S.; Sharpless, K. B.
J . Org. Chem. 1981, 46, 3936.
(23) Buckleton, J . S.; Cambie, R. C.; Clark, G. R.; Craw, P. A.;
Rickard, C. E. F.; Rutledge, P. S.; Woodgate, P. D. Aust. J . Chem. 1988,
41, 305.
(24) Cassity, R. P.; Taylor, L. T.; Wolfe, J . F. J . Org. Chem. 1978,
43, 2286.
(25) Paine, J . B., III. J . Heterocycl. Chem. 1991, 28, 1463.
(26) Greenhill, J . V.; Loghmani-Khouzani, H. Tetrahedron 1988, 11,
3319.
(27) Elguero, J .; Marzin, C.; Katritzky, A. R., Linda, P. The Tau-
tomerism of Heterocycles; Academic Press: London, 1976; Vol. 2, p 187.
(28) Foster, A. B.; J arman, M.; Leung, C.; Rowlands, M. G.; Taylor,
G. N. J . Med. Chem. 1985, 28, 200.
(29) Martin, M. L.; Marin, G. J . Manuel de Re´sonance Magne´tique
Nucle´aire; Azoulay, Ed.; Paris, 1971.
acids 15 in moderate to good yields. Other systems such
21
22
as O3 and KIO4/RuCl3 did not provide better results.
Cleavage of the pivaloyl moiety with hot aqueous sulfuric
acid afforded amino acids 15. Finally, highly diluted
cyclization11 of the latter compounds, 15, led to the
desired analogues 5a ,b (Scheme 5).
It should be noted that lactam 5b, bearing a stereo-
genic carbon besides its axial chirality, is seen as a single
diastereoisomer by NMR and HPLC analysis (even at 5
°C). This means that either rotation around the biarylic

Phenylpyridine Analogues of Rhazinilam
J . Org. Chem., Vol. 66, No. 8, 2001 2657
Sch em e 6a
Sch em e 7a
a
(i) (R ) Me) (1) NH2NH2‚H2O, ethylene glycol, 150-160 °C, 4
h, (2) KOH, 160 °C, 3 h then HCl. (ii) NaBH4, EtOH, 20 °C, 4 h (R
) Me) or 16 h (R ) Et). (iii) HMPA, 1 equiv H2SO4, 215-220 °C/1
h (R ) Me) or 220-225 °C/1.5 h (R ) Et). (iv) H2, Pd-C, MeOH,
1 atm, 20 °C, 1 h. (v) H2SO4 30%, 160 °C, 2 h then NH4OH 25%.
(vi) HOBT, EDCI, NEt3, CHCl3, 36 h, reflux (R ) Me) or 50 °C (R
) Et).
a
(i) (1) 1.1 equiv of n-BuLi, THF, -20 °C, 1 h; (2) CH3CONMe2,
-70 °C, 30 min then H2O. (ii) (1) 1 equiv of n-BuLi, THF, -70
°C/10 min then -70 °C f 20 °C in 40 min; (2) 1-1.2 equiv RI, 20
°C/16 h (R) Me) or reflux/16 h (R ) Et). (iii) acrylonitrile,
BnMe3N+OH-, t-BuOH, 25 °C, 16 h (R ) Me) or 7 days (R ) Et).
Ta ble 1. Dia ster eoisom er ic Ra tio
two or more diastereoisomers (see Experimental Section
for diastereoisomeric ratios).
time (in hours)
needed to reach
equilibrium
temp
diastereoisomeric
Red u ction of Keto Der iva tives 18 to Alk a n es. The
modified Wolff-Kishner conditions used with success for
model studies13 were inapplicable. Despite the formations
at least partiallysof the hydrazone derived from 18a , as
product
solvent
CDCl3
(°C) ratio (at equilibrium)
18a
25
40
22
25
40
25
3.1:1
3.1:1
2:1
3.1:1
3.1:1
2.2:1
25
4
1.5
98
10
2
DMSO-d6
CDCl3
1
18b
evidenced by H NMR, basic treatment of the latter did
not afford the desired alkane. Instead, imine 20 was
isolated, together with a small amount of the strong base-
induced deacetylated product31,32 21 (Scheme 7). To avoid
these unwanted reactions, ketones 18 were first reduced
to the corresponding alcohols 22 with NaBH4 and then
dehydrated to 23 in hot HMPA.33,34 Provided that a small
amount of sulfuric acid was added, the latter key reaction
was clean, but we could not totally avoid the formation
of byproducts 23c,d due to ethanolic chain cleavage.
Vinyl compounds 23a ,b were then converted to alkanes
DMSO-d6
respectively, for 18a (R ) Me) and 18b (R ) Et). These
values, indicative of the presence of true atropoisomers,
are quite unusual for biaryl compounds with only one
substituent at each ortho-position. Contrary to this,
tertiary compounds 17 showed a very quick interconver-
sion at room temperature (NMR and HPLC), thus
indicating the presence of conformers rather than dias-
tereoisomers.30 In the next part, all the compounds will
be described as only one product, even if they exist as
(31) Meerwein Liebigs Ann. Chem. 1913, 396, 242.
(32) Calas, M.; Calas, B.; Giral, L. Bull. Soc. Chim. Fr. 1973, 6, 2079.
(33) Monson, R. S.; Priest, D. N. J . Org. Chem. 1971, 36, 3826.
(34) Monson, R. S. Tetrahedron Lett. 1971, 7, 567.
(30) Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds;
Wiley & Sons: New York, 1994.

2658 J . Org. Chem., Vol. 66, No. 8, 2001
Pasquinet et al.
Sch em e 8a
24a ,b by a catalytic hydrogenation. The resulting amines
were finally deprotected to the corresponding amino acids
25 by aqueous sulfuric acid treatment. 1H NMR indicated
that the latter adopted a zwitterionic-type structure in
CDCl3, it was not the case in DMSO. After cyclization,
using the HOBT/EDCI system, target lactams 5c,d were
obtained in good yields (Scheme 7). Starting from 25a
(diastereoisomeric ratio 1:1), lactamization gave a dias-
tereoisomeric ratio of 2.7:1 for 5c, each of which could
be separated by HPLC.
Following a similar strategy, an analogue with a vinyl
appendage 5e was prepared from 23a . Interestingly,
attempted amine deprotection of alkene 23b led to a
tricyclic product 27, probably via a SEAr2 process (Scheme
7).
Ca r ba m a te An a logu e. Starting with our key inter-
mediate 9, we were able to synthesize an analogue with
a cyclic carbamate functionality. Again, the strategy
involves the introduction of an activating group at the
picolinic position, namely an ester. Thus, treatment of 9
with n-BuLi/t-BuONa/diisopropylamine35 (“NDA”) at low
temperature, followed by reaction of the resulting anion
with diethyl carbonate yielded 91% of the corresponding
ester 28. Diethylation of the latter gave 60% of 29. The
LiAlH4 reduction of 29 was quite difficult, and only 28%
(best conditions) of the corresponding alcohol 30 were
obtained. We recovered 64% of starting material together
with 4% of product 31 arising from reduction of both ester
and amide functionalities. The presence of the latter
compound prevented us from using higher temperature
and/or reaction times. To circumvent the problematic
reduction of amidoester 29, we considered its prior
hydrolysis to the corresponding amino acid which could
be reduced more easily. However, treatment of 29 with
aqueous H2SO4 did not afford the target compound, but
rather the seven-membered ring lactam 32. Therefore,
we had to carry on the synthesis from hydroxy amide 30,
which was hydrolyzed to the corresponding amino alcohol
33. Treatment of the latter with triphosgen12,36 (Cl3-
COCO2CCl3) led to the desired analogue 6 possessing a
carbamate function (Scheme 8) (AB-type signals were
a
(i) (1) 3.5 equiv of NDA, THF, -70 °C, 1 h; (2) 3.5 equiv of
(EtO)2CO, -70 °C, 40 min. (ii) (1) 3.1 equiv of LDA, THF, -70 °C,
10 min; (2) 3.1 equiv of EtI, -70 °C f 20 °C, 3 h, (3) idem. 1. (4)
idem. 2. (iii) LiAlH4, THF, 40 °C, 4 h. (iv) H2SO4 30%, 160 °C, 2 h
then NH4OH 25%. (v) Cl3COCO2CCl3, DMAP, CH2Cl2, -70 °C,
15 min then -70 °C f 20 °C, 4 h.
1
observed by H NMR for CH2 protons throughout this
synthesis, again highlighting the asymmetry brought by
the biaryl linkage).
Biologica l Resu lts. Besides the synthesis of new
tricyclic hindered phenylpyridine lactams, the aim of this
study was to show if the phenylpyrrole moiety of rhazi-
nilam 1 could be replaced by a phenylpyridine system
without affecting the interaction with tubulin. The novel
phenylpyridine compounds 5 and 6 were tested, under
their racemic form, for their ability to inhibit the cold-
disassembly of microtubules.7 Each diastereoisomers 5c
and 5e were assayed separately after separation by
HPLC. Compounds 5a , 5b, and 5c were found inactive,
whereas 5d , 5e (major diastereoisomer), and 6 interact
with tubulin. This implies that the bulkiness of the
substituents at the picolinic carbon is important for
24 µM),11,12 and modification of the lactam to an urethane
function increases the activity. Thus, compound 6 (IC50
) 18µM) is slightly more active than 5d (IC50 ) 28µM),
but possesses a weaker activity as compared to racemic
biphenyl 4 (IC50 ) 3 µM). Knowing the acidic character
of tubulin, the lower activity of 5d and 6 may be due to
the protonation of the pyridine ring leading to an
unfavorable charge distribution37 for the interaction with
tubulin. It must be mentioned that the overall conforma-
tion and charge distribution37 of 5d and 6 is similar to
that of the biphenyl compounds 3 (R ) Et) and 4,
respectively. Regarding the cytotoxicity of the compounds
on KB cells,38 there is a good correlation with the
microtubules disassembly assay, compound 6 being the
most cytotoxic but 8 times less cytotoxic than rhazinilam
(IC50 ) 2 µM).
antitubulin activity. Compared to rhazinilam 1 (IC50
3 µM), compounds 5d , 5e, and 6 were, respectively, 9.5,
)
14, and 6 times less active. All three analogues possess
similar activity to that of the biphenyl 3 (R ) Et, IC50
)
(37) Molecular modeling studies were performed on a Silicon Graph-
ics Indigo II (R10000) workstation, using Sybyl from Tripos (force
field: MMFF94) for the generation of conformers and MOPAC (AM1)
for evaluation of charge distribution.
(35) Klusener, P. A. A.; L. Tip, L.; Brandsma, L. Tetrahedron 1991,
47, 2041.
(36) Cotarca, L.; Delogu, P.; Nardelli, A.; Sunjic, V. Synthesis 1996,
553.
(38) Borenfreund, E.; Puerner, J . A. Toxicol. Lett. 1985, 24, 119.

Phenylpyridine Analogues of Rhazinilam
J . Org. Chem., Vol. 66, No. 8, 2001 2659
°C for 40 min. The residue was Kugelrohr distilled (180 °C/
0.6 mbar) to yield 13b (1.99 g, 81%), as an orange viscous oil
(1:1 mixture of diastereoisomers). 1H NMR (200 MHz, CDCl3)
δ 0.65, 0.79 (2d, J ) 7.4, 3H), 1.03 (s, 9H), 1.60-1.94 (m, 6H),
2.62 (m, 1H), 4.86 (m, 2H), 5.65 (m, 1H), 6.91 (br s, 1H), 7.18
(m, 3H), 7.42 (m, 1H), 7.48 (m, 1H), 8.39 (d, J ) 8.2, 1H), 8.72
(m, 1H). 13C NMR (50 MHz, CDCl3) δ 12.0, 12.2, 27.1, 27.3,
28.0, 31.6, 31.9, 34.0, 34.2, 39.6, 43.5, 43.6, 114.2, 114.5, 120.5,
121.0, 123.4, 128.8, 128.9, 129.8, 129.9, 132.4, 132.5, 135.5,
137.5, 137.8, 138.5, 149.7, 163.8, 163.9, 176.0. IR (thin film)
3365, 1692, 1001, 916 cm-1. Anal. Calcd for C23H30N2O
(350.51): C, 78.82; H, 8.63; N, 7.99. Found: C, 78.98; H, 8.63;
Con clu sion
For the first time, analogues of rhazinilam 1 possessing
a phenylpyridine structure were prepared. Lactams
bearing a secondary or tertiary picolinic carbon were first
obtained, thanks to key steps such as lateral metalation
and cross-coupling. The synthesis of lactams with a
quaternary picolinic carbon was then achieved, the
reduction of an acetyl group to an ethyl group being the
crucial step. Compounds 5 were obtained in five to nine
steps with overall yields of 5.1% to 31.3% depending on
the structure. In this pyridine series, biological assays
showed that a fully substituted picolinic carbon was
needed for interaction of the lactams with tubulin, as
evidenced in pyrrole or phenyl series. However, the best
results were obtained for cyclic carbamate 6, which was
synthesized using a similar strategy. Racemic 6 is six
times less active than the parent (-)-rhazinilam 1, which
means that the active enantiomer of the former would
be only three times less active than 1. The strategy is
currently being extended to the preparation of other
phenylpyridine analogues of rhazinilam.
N, 8.11. Refractive index: η20 ) 1.5508.
D
10,11,12,13-Tet r a h yd r o-9H -b en zo[b]p yr id o[3,2-d ]a zo-
n in -10-on e (5a ). This procedure is general for the lactamiza-
tion of amino acids. To a suspension of HOBT (297 mg, 2.2
mmol), EDCI (422 mg, 2.2 mmol), and amino acid 15a (564
mg, 2.2 mmol) in ethanol-free CH2Cl2 (1300 mL) was added
triethylamine (306 µL). The mixture was stirred at 40 °C for
24 h, after which the solvent was evaporated. The residue was
subjected to chromatography (95:5 CH2Cl2/MeOH) to yield 5a
(294 mg, 56%), as a yellow solid, mp 192 °C.1H NMR (400 MHz,
CDCl3) δ 1.95 (m, 2H), 2.06 (m, 2H), 2.26 (m, 1H), 2.82 (m,
1H), 7.06 (dd, J ) 7.6 and 4.8, 1H), 7.22 (dd, J ) 7.6 and 1.8,
1H), 7.25 (m, 2H), 7.40 (m, 2H), 7.78 (br s, 1H), 8.51 (dd, J )
4.8 and 1.8, 1H). 13C NMR (50 MHz, CDCl3) δ 25.9, 33.9, 36.9,
120.8, 128.6, 129.0, 129.1, 129.4, 133.7, 136.0, 140.6, 149.4,
158.9, 176.2. IR (KBr) 3168, 1654 cm-1. MS (CI, t-BuH) m/z
239 (M + H)+. Anal. Calcd for C15H14N2O (238.29): C, 75.60;
H, 5.92; N, 11.76. Found: C, 75.39; H, 5.86; N, 11.78.
13-E t h yl-10,11,12,13-t et r a h yd r o-9H -b en zo[b]p yr id o-
[3,2-d ]a zon in -10-on e (5b). The same procedure as above was
applied to amino acid 15b (142 mg, 0.5 mmol), the reaction
mixture being stirred at room temperature for 48 h. The
solvent was evaporated and the residue chromatographed (9:1
CH2Cl2/MeOH) to yield 5b (100 mg, 75%), as a yellow solid,
mp 186 °C.1H NMR (200 MHz, CDCl3) δ 0.60 (t, J ) 7.2, 3H),
1.48 (m, 1H), 1.73-2.28 (m, 6H), 7.11 (dd, J ) 7.6 and 4.8,
1H), 7.23 (br s, 1H), 7.30 (m, 3H), 7.46 (m, 2H), 8.65 (dd, J )
4.8 and 1.8, 1H). 13C NMR (50 MHz, CDCl3) δ 12.3, 28.6, 32.8,
34.3, 47.2, 121.5, 129.0, 129.2, 129.4, 129.8, 135.4, 136.4, 137.2,
140.5, 148.9, 160.9, 176.2. IR (KBr) 3208, 1648 cm-1. MS (CI,
NH3) m/z 267 (M + H)+. Anal. Calcd for C17H18N2O (266.34):
C, 76.66; H, 6.81; N, 10.52. Found: C, 76.24; H, 6.88; N, 10.55.
2,2-Dim et h yl-N-(2-(2-(1-(2-oxop r op yl)-1-m et h yl-3-cy-
a n op r op yl)-3-p yr id yl)p h en yl)p r op a n a m id e (18a ). To a
solution of ketone 17a (1.46 g, 4.5 mmol) in t-BuOH (10 mL)
were added dropwise BnMe3NOH (40% solution in methanol,
99 µL, 0.22 mmol) and then acrylonitrile (0.59 mL, 9 mmol).
After 16 h of stirring at room temperature, the reaction
mixture was hydrolyzed (10 mL of water), followed by extrac-
tion with CH2Cl2. The organic extract was dried, and the
solvent was evaporated. The residue was subjected to chro-
matography (96:4 CH2Cl2/CH3CN) to yield 18a (1.39 g, 82%),
as a colorless viscous oil (3:1 mixture of diastereoisomers). 1H
NMR (300 MHz, CDCl3) δ 1.04 (s, 2.2H), 1.06 (s, 6.8H), 1.35
(s, 2.3H), 1.38 (s, 0.7H), 1.69 (s, 0.7H), 1.76 (s, 2.3H), 2.09-
2.67 (m, 4H), 6.89 (br s, 0.25H), 7.09 (br s, 0.75H), 7.16 (m,
2H), 7.30 (m, 1H), 7.40 (m, 2H), 8.05 (d, J ) 8.0, 0.75H), 8.06
(d, J ) 8.0, 0.25H), 8.61 (dd, J ) 4.7 and 1.8, 0.75H), 8.64 (dd,
J ) 4.7 and 1.8, 0.25H). 13C NMR (75 MHz, CDCl3) δ 13.4,
13.6, 23.5, 24.9, 26.4, 26.9, 27.7, 34.6, 34.7, 39.9, 58.6, 119.9,
120.5, 122.4, 122.6, 123.9, 124.0, 124.3, 130.1, 130.2, 130.4,
130.6, 131.2. 133.5, 133.6, 136.3, 136.5, 140.6, 140.9, 148.8,
159.3, 159.7, 176.8, 210.3, 211.0. IR (thin film) 2246, 1713,
1689 cm-1. Anal. Calcd for C23H27N3O2 (377.49): C, 73.18; H,
7.21; N, 11.13. Found: C, 73.61; H, 7.25; N, 11.13.
Exp er im en ta l Section
Gen er a l Da ta . See refs 16 and 19. Organic layers were
dried with MgSO4. Silica gel was used for all flash chromatog-
raphies. 1H-1H NMR coupling constants for aromatic protons
and ethyl moiety are consistent with those of the literature
and are given in hertz.
2,2-Dim eth yl-N-(2-(2-(1-eth ylp r op -1-yl)-3-p yr id yl)p h e-
n yl)p r op a n a m id e (12). To a suspension of potassium tert-
butoxide (363 mg, 3.2 mmol) in THF (4 mL) was added
diisopropylamine (0.45 mL, 3.2 mmol). The mixture was cooled
to -70 °C, and n-BuLi (1.3 mL, 3.2 mmol) was slowly added.
The reaction mixture was then warmed to -50 °C over 15 min
before adding a solution of propylpyridine 10 (274 mg, 0.92
mmol) in THF (2 mL). After 30 min of stirring and then cooling
to -70 °C, iodoethane (0.28 mL, 3.5 mmol) was added drop-
wise. After 15 min of stirring at -70 °C the reaction mixture
was hydrolyzed (3 mL of water), followed by extraction with
CH2Cl2. The combined organic extracts were dried, and the
solvent was evaporated. The residue was subjected to chro-
matography (1:9 EtOAc/cyclohexane) to yield 12 (263 mg, 88%),
as a white solid, mp 137 °C. 1H NMR (200 MHz, CDCl3) δ 0.62
(t, J ) 7.3, 3H), 0.75 (t, J ) 7.3, 3H), 1.00 (s, 9H), 1.61 (q, J )
7.3, 4H), 2.47 (q, J ) 7.3, 1H), 6.96 (br s, 1H), 7.12 (m, 3H),
7.45 (m, 2H), 8.36 (d, J ) 8.1, 1H), 8.69 (dd, J ) 4.8 and 1.8,
1H). 13C NMR (50 MHz, CDCl3) δ 11.9, 12.2, 27.0, 27.9, 39.4,
45.4, 120.2, 120.9, 123.3, 128.6, 129.0, 129.7, 132.4, 135.4,
137.2, 149.5, 163.8, 175.7. IR (KBr) 3334, 1647 cm-1. Anal.
Calcd for C21H28N2O (324.47): C, 77.74; H, 8.70; N, 8.63.
Found: C, 77.57; H, 8.65; N, 8.59.
2,2-Dim eth yl-N-(2-(2-p en t-4-en yl-3-p yr idyl)ph en yl)pr o-
p a n a m id e (13a ). The same procedure as for the synthesis of
10 (see Supporting Information) was applied to picoline 9 (3.76
g, 14 mmol), reacting 4-bromobut-1-ene as electrophile over 1
h while raising the temperature from -50 °C to 0 °C. The
residue was Kugelrohr distilled (180 °C/0.6 mbar) to yield 13a
1
(3.85 g, 85%), as a pale yellow oil. H NMR (200 MHz, CDCl3)
δ 1.03 (s, 9H), 1.64-1.96 (m, 4H), 2.60 (m, 2H), 4.86 (d, J )
10.4, 1H), 4.89 (d, J ) 17.0, 1H), 5.65 (ddt, J ) 17.0, 10.4, 6.5,
1H), 6.95 (br s, 1H), 7.16 (m, 2H), 7.26 (dd, J ) 7.6 and 4.8,
1H), 7.44 (m, 1H), 7.51 (dd, J ) 7.6 and 1.8, 1H), 8.37 (d, J )
8.2, 1H), 8.66 (dd, J ) 4.8 and 1.8, 1H). IR (thin film) 3346,
1692 cm-1. Anal. Calcd for C21H26N2O (322.45): C, 78.22; H,
8.13; N, 8.69. Found: C, 77.88; H, 8.11; N, 8.62. Refractive
2,2-Dim eth yl-N-(2-(2-(1-(2-oxop r op yl)-1-eth yl-3-cya n o-
p r op yl)-3-p yr id yl)p h en yl)p r op a n a m id e (18b). To a solu-
tion of ketone 17b (2.465 g, 7.6 mmol) in t-BuOH (100 mL)
was added dropwise BnMe3NOH (40% solution in methanol,
167 µL, 0.38 mmol) and then acrylonitrile (0.75 mL, 11.4
mmol). The mixture was stirred for 7 days, during which
several portions of BnMe3NOH (0.167 mL, 0.38 mmol each
portion) and acrylonitrile (0.25 mL, 3.8 mmol each portion)
index: η20 ) 1.5515.
D
2,2-Dim et h yl-N-(2-(2-(1-et h ylp en t -4-en yl)-3-p yr id yl)-
p h en yl)p r op a n a m id e (13b). The same procedure as for the
synthesis of 12 was applied to the propyl compound 10 (2.075
g, 7 mmol) reacting 4-bromobut-1-ene as electrophile at -40

2660 J . Org. Chem., Vol. 66, No. 8, 2001
Pasquinet et al.
were added. The solvent was evaporated and the residue taken
up in THF (30 mL). 1 N aqueous HCl (20 mL) was added and
the mixture stirred at room temperature for 1 h. After
decantation and one extraction with Et2O, the combined
organic extracts were dried and concentrated. The residue was
subjected to chromatography (9:1 CH2Cl2/CH3CN) to yield 18b
(774 mg, 26%), as a waxy yellow solid (3:1 mixture of
Calcd for C23H29N3O (363.51): C, 76.00; H, 8.04; N, 11.56.
Found: C, 75.83; H, 8.08; N, 11.56.
2,2-Dim eth yl-N-(2-(2-(1.1-d ieth yl-3-cya n op r op yl)-3-p y-
r id yl)p h en yl)p r op a n a m id e (24b). The same procedure as
above was applied to alkene 23b (173 mg, 0.46 mmol) to yield
1
24b (161 mg, 93%) as a pale yellow viscous oil. H NMR (300
MHz, CDCl3) δ 0.56 (t, J ) 7.3, 3H), 0.61 (t, J ) 7.3, 3H), 0.94
(s, 9H), 1.36-1.69 (m, 4H), 1.91-2.33 (m, 4H), 6.78 (br s, 1H),
7.05 (m, 2H), 7.18 (dd, J ) 7.7 and 4.8, 1H), 7.33 (m, 2H), 8.28
(d, J ) 8.1, 1H), 8.62 (dd, J ) 4.8 and 1.8, 1H). 13C NMR (75
MHz, CDCl3) δ 9.1, 13.0, 27.6, 27.7, 29.2, 31.6, 40.1, 49.8, 120.7,
121.6, 121.8, 123.8, 129.6, 129.9, 131.5. 133.5, 136.0, 141.7,
148.4, 162.1, 176.5. IR (thin film) 2245, 1687 cm-1. Anal. Calcd
for C24H31N3O (377.53): C, 76.36; H, 8.28; N, 11.13. Found:
C, 76.14; H, 8.26; N, 11.11.
4-(3-(2-An ilin o)-2-pyr idyl)-4-m eth ylh exan oic acid (25a).
The same procedure as for the synthesis of 15a was applied
to pivalamide 24a (131 mg, 0.36 mmol). Chromatography (94:6
CH2Cl2/MeOH) yielded 25a (83 mg, 77%) as a pale brown
viscous oil (1:1 mixture of diastereoisomers). 1H NMR (300
MHz, CDCl3) δ 0.61 (t, J ) 7.4, 3H), 0.97, 1.04 (2s, 3H), 1.35-
2.30, 2.50 (2m, 6H), 6.07 (br s, 3H), 6.67 (m, 2H), 6.88 (m, 1H),
7.12 (m, 2H), 7.31, 7.33 (2dd, J ) 7.6 and 1.8, 1H), 8.51 (m,
1H). 13C NMR (75 MHz, CDCl3) δ 9.4, 9.6, 23.0, 24.2, 31.2,
35.1, 36.4, 37.1, 46.7, 115.6, 115.9, 118.1, 118.3, 121.6, 127.4,
127.5, 129.3, 130.6, 130.9, 134.7, 135.0, 141.6, 141.8, 143.8,
144.1, 147.7, 147.8, 163.8, 179.2. IR (thin film) 3377, 1617
cm-1. Anal. Calcd for C18H22N2O2 (298.39): C, 72.46; H, 7.43;
N, 9.39. Found: C, 72.78; H, 7.41; N, 9.38.
4-(3-(2-An ilin o)-2-p yr id yl)-4-eth ylh exa n oic Acid (25b).
The same procedure as for the synthesis of 15a was applied
to pivalamide 24b (136 mg, 0.36 mmol). Chromatography (97:3
CH2Cl2/MeOH) yielded 25b (104 mg, 92%) as a pale brown
solid, mp 120 °C. 1H NMR (300 MHz, CDCl3) δ 0.58 (t, J )
7.3, 6H), 1.48-1.68 (m, 4H), 1.95, 2.12 (2m, 4H), 5.50 (br s,
3H), 6.66 (m, 2H), 6.89 (dd, J ) 7.4 and 1.5, 1H), 7.13 (m, 2H),
7.31 (dd, J ) 7.7 and 2.2, 1H), 8.52 (dd, J ) 4.6 and 2.2, 1H).
13C NMR (75 MHz, CDCl3) δ 8.7, 8.8, 27.5, 28.9, 30.3, 30.8,
49.8, 115.7, 118.0, 121.5, 127.0, 129.2, 130.3, 134.9, 142.1,
143.6, 147.0, 163.5, 178.1. IR (KBr) 3364, 1625 cm-1. Anal.
Calcd for C19H24N2O2 (312.42): C, 73.04; H, 7.77; N, 8.97.
Found: C, 73.18; H, 7.78; N, 9.01.
4-(3-(2-An ilin o)-2-p yr id yl)-4-m et h ylh ex-5-en oic Acid
(26). The same procedure as for the synthesis of 15a (see
Supporting Information) was applied to pivalamide 23a (70
mg, 0.19 mmol). Chromatography (9:1 CH2Cl2/MeOH) yielded
26 (44 mg, 77%) as a yellow viscous oil (1:1 mixture of
diastereoisomers). 1H NMR (300 MHz, CDCl3) δ 1.11, 1.18 (2s,
3H), 1.81-2.23 (m, 4H), 4.50, 4.63 (2d, J ) 10.2, 1H), 4.55,
4.64 (2d, J ) 17.6, 1H), 5.45 (br s, 3H), 5.76, 5.83 (2dd, J )
17.6 and 10.2, 1H), 6.57 (m, 2H), 6.75, 6.80 (2dd, J ) 7.5 and
1.1, 1H), 7.03 (m, 2H), 7.27 (m, 1H), 8.45 (m, 1H). 13C NMR
(75 MHz, CDCl3) δ 23.6, 25.5, 31.8, 37.0, 37.3, 48.3, 48.5, 111.6,
111.8, 115.5, 117.5, 117.8, 121.7, 126.9, 127.2, 129.2, 129.3,
131.2, 131.5, 134.3, 141.2, 141.3, 144.3, 144.5, 144.5, 145.9,
148.1, 148.2, 163.7, 164.2, 180.6, 180.8. IR (thin film) 1616,
1000, 909 cm-1. Anal. Calcd for C18H20N2O2 (296.37): C, 72.95;
H, 6.80; N, 9.45. Found: C, 72.74; H, 6.84; N, 9.41.
1
diastereoisomers). H NMR (300 MHz, CDCl3) δ 0.59 (t, J )
7.5, 2.3H), 0.70 (t, J ) 7.5, 0.7H), 0.99 (s, 9H), 1.49 (s, 0.7H),
1.65 (s, 2.3H), 1.67-2.41 (m, 4.5H), 2.58 (m, 1.5H), 6.88 (br s,
0.25H), 6.99 (br s, 0.75H), 7.08 (m, 2H), 7.20 (m, 1H), 7.36 (m,
2H), 7.89 (d, J ) 7.7, 0.25H), 7.95 (d, J ) 7.7, 0.75H), 8.55 (m,
1H). 13C NMR (75 MHz, CDCl3) δ 9.14, 13.0, 13.5, 27.1, 27.6,
28.3, 28.7, 29.9, 31.0, 31.1, 39.8, 61.8, 62.7, 120.5, 122.2, 122.3,
124.2, 124.4, 124.9, 130.0, 130.2, 130.5, 131.3. 131.5, 133.9,
136.3, 136.6, 140.6, 140.8, 148.2, 148.4, 158.2, 158.9, 176.9,
177.0, 210.6, 211.6. IR (thin film) 2247, 1710, 1682 cm-1. Anal.
Calcd for C24H29N3O2 (391.52): C, 73.63; H, 7.47; N, 10.73.
Found: C, 73.68; H, 7.54; N, 10.86. During purification,
compound 19 was isolated in small amounts.
2,2-Dim eth yl-N-(2-(2-(1-m eth yl-1-vin yl-3-cya n op r op yl)-
3-p yr id yl)p h en yl)p r op a n a m id e (23a ). A solution of alcohol
22a (171 mg, 0.45 mmol) in HMPA (1 mL) containing concd
sulfuric acid (12.5 µL) was heated at 220 °C for 1 h. The solvent
was removed by Kugelrohr distillation (130 °C/1 mbar) and
the residue chromatographed (1:2 EtOAc/petroleum ether) to
yield 23a (99 mg, 61%) as an orange viscous oil (1:1 mixture
1
of diastereoisomers). H NMR (300 MHz, CDCl3) δ 0.92, 0.93
(2s, 9H), 1.18, 1.23 (2s, 3H), 2.04-2.40 (m, 4H), 4.65, 4.68 (2d,
J ) 17.4, 1H), 4.70, 4.71 (2d, J ) 10.8, 1H), 5.60, 5.66 (2dd, J
) 17.4, 10.8, 1H), 6.67, 6.71 (2br s, 1H), 7.03 (m, 2H), 7.26 (m,
1H), 7.33 (m, 2H), 8.13, 8.17 (2d, J ) 8.2, 1H), 8.61 (m, 1H).
13C NMR (75 MHz, CDCl3) δ. 11.9, 22.2, 23.0, 26.9, 35.9, 38.6,
46.8, 46.9, 112.6, 119.1, 119.4, 120.0, 120.3, 120.5, 120.7, 122.2,
128.1, 128.2, 129.1, 129.6, 129.8. 131.6, 134.6, 139.4, 140.6,
142.0, 147.6, 147.8, 160.7, 161.1, 174.9, 175.0. IR (thin film)
2361, 1001, 919 cm-1. Anal. Calcd for C23H27N3O (361.49): C,
76.42; H, 7.53; N, 11.62. Found: C, 76.20; H, 7.51; N, 11.54.
2,2-Dim eth yl-N-(2-(2-(1-Eth yl-1-vin yl-3-cya n op r op yl)-
3-p yr id yl)p h en yl)p r op a n a m id e (23b). The same procedure
as above was applied to alcohol 22b (177 mg, 0.45 mmol), with
a reaction time of 1.5 h to yield 23b (71 mg, 42%) as a pale
1
yellow viscous oil (1:1 mixture of diastereoisomers). H NMR
(300 MHz, CDCl3) δ 0.59, 0.65 (2t, J ) 7.3, 3H), 0.92, 0.94 (2s,
9H), 1.50-2.48 (m, 6H), 4.56, 4.63 (2d, J ) 17.6, 1H), 4.66,
4.71 (2d, J ) 11.0, 1H), 5.49, 5.54 (2dd, J ) 17.6 and 11.0,
1H), 6.67, 6.74 (2br s, 1H), 7.00 (m, 2H), 7.20 (m, 1H), 7.33
(m, 2H.), 8.11, 8.17 (2d, J ) 8.0, 1H), 8.63 (m, 1H). 13C NMR
(75 MHz, CDCl3) δ 8.5, 8.8, 12.6, 12.8, 27.4, 28.6, 29.0, 32.1,
32.2, 39.7, 39.8, 51.0, 51.2, 113.8, 114.8, 120.3, 120.7, 121.1,
121.3, 121.6, 121.8, 123.1, 129.3, 129.7, 130.3, 130.4, 130.7.
133.1, 133.5, 135.9, 139.4, 140.5, 140.6, 140.8, 141.3, 161.1,
161.2, 176.0, 176.1. IR (thin film) 2246, 1001, 919 cm-1. Anal.
Calcd for C24H29N3O (375.52): C, 76.77; H, 7.78; N, 11.19.
Found: C, 76.95; H, 7.68; N, 11.21.
During purification of compounds 23a ,b, compounds 23c,d
were isolated in 24% and 42%, respectively.
2,2-Dim eth yl-N-(2-(2-(1-eth yl-1-m eth yl-3-cya n op r op yl)-
3-p yr id yl)p h en yl)p r op a n a m id e (24a ). To a solution of
alkene 23a (166 mg, 0.46 mmol) in methanol (5 mL) was added
palladium on carbon (5%, 60 mg, 0.028 mmol). The mixture
was stirred at room temperature for 1 h under 1 atm of
hydrogen. After a N2 flush, the mixture was filtered and the
filtrate evaporated. The residue was subjected to chromatog-
raphy (98:2 CH2Cl2/MeOH) to yield 24a (152 mg, 91%) as a
white solid (1:1 mixture of diastereoisomers). 1H NMR (300
MHz, CDCl3) δ 0.61, 0.64 (2t, J ) 7.3, 3H), 0.83, 0.87 (2s, 3H),
0.94 (s, 9H), 1.25-2.25, 2.75 (2m, 6H), 6.77, 6.80 (2br s, 1H),
7.04 (m, 2H), 7.18 (m, 1H), 7.33 (m, 2H), 8.27, 8.29 (2d, J )
8.4, 1H), 8.61 (m, 1H). 13C NMR (75 MHz, CDCl3) δ 9.2, 9.6,
13.3, 13.6, 23.3, 24.1, 27.7, 34.6, 36.0, 36.7, 38.3, 40.1, 46.2,
46.4, 112.6, 120.7, 120.9, 121.3, 121.5, 123.6, 123.7, 129.5,
129.9, 130.2, 131.3. 132.8, 133.2, 136.0, 140.9, 148.8, 149.0,
162.6, 162.7, 176.3, 176.4. IR (KBr) 2246, 1683 cm-1. Anal.
13-E t h yl-13-m et h yl-10,11,12,13-t et r a h yd r o-9H -b en zo-
[b]p yr id o[3.2-d ]a zon in -10-on e (5c). The same procedure as
for the synthesis of 5a was applied to amino acid 25a (39 mg,
0.13 mmol), the reaction mixture (solvent: CHCl3) being
refluxed for 36 h with introduction of an additional 0.5 equiv
of HOBT/EDCI/NEt3 after 24 h. The solvent was evaporated
and the residue chromatographed (93:7 CH2Cl2/MeOH) to yield
5c (26 mg, 71%), as a white solid (2.7:1 mixture of diastere-
1
oisomers). H NMR (300 MHz, CDCl3, 40 °C) δ 0.50 (t, J )
7.3, 2.2H), 0.63 (t, J ) 7.3, 0.8H), 0.72 (s, 0.8H), 1.12-1.70,
2.05-2.65 (2m, 8.2H), 5.80 (br s, 0.27H), 6.96 (dd, J ) 7.6 and
4.7, 0.27H), 7.00 (dd, J ) 7.6 and 4.7, 0.73H), 7.08 (m, 1H),
7.20 (m, 1H), 7.31 (m, 3H), 7.72 (br s, 0.73H), 8.51 (m, 1H).
(
13C NMR Problems of relaxation affect the NMR spectrum,
and peaks are missing, especially in the aliphatic area.) (75
MHz, CDCl3) δ 9.1, 46.2, 46.8, 120.5, 120.8, 128.3, 128.6, 129.5,
129.7, 128.5, 128.7, 129.4, 131.1, 133.4, 135.7, 136.4, 138.4,

Phenylpyridine Analogues of Rhazinilam
J . Org. Chem., Vol. 66, No. 8, 2001 2661
143.1, 143.3, 148.7, 148.9. IR (KBr) 1659 cm-1. MS (CI, t-BuH)
m/z 281 (M + H)+. Anal. Calcd for C18H20N2O (280.37): C,
77.11; H, 7.19; N, 9.99. Found: C, 76.68; H, 7.22; N, 10.00.
Diastereoisomers were separated by semipreparative HPLC.
mps: 164 °C (major diastereoisomer) and 198 °C (minor
diastereoisomer).
subjected to chromatography (1:4 EtOAc/petroleum ether) to
yield 29 (119 mg, 60%), as a white solid, mp 107 °C. H NMR
1
(300 MHz, CDCl3) δ 0.57 (t, J ) 7.5, 3H), 0.72 (t, J ) 7.5, 3H),
0.88 (t, J ) 7.1, 3H), 0.96 (s, 9H), 1.86-2.12, 2.30 (2m, 4H),
3.40 (dq, J ) 11.0 and 6.9, 1H), 3.70 (dq, J ) 11.0 and 6.9,
1H), 7.08 (m, 2H), 7.12 (dd, J ) 7.7 and 1.8, 1H), 7.19 (br s,
1H), 7.25 (dd, J ) 7.7 and 4.8, 1H), 7.30 (m, 1H), 7.82 (d, J )
7.8, 1H), 8.56 (dd, J ) 4.8 and 1.8, 1H). 13C NMR (75 MHz,
CDCl3) δ 8.5, 8.8, 13.9, 26.6, 27.3, 28.2, 39.5, 58.0, 60.8, 121.3,
124.0, 124.5, 129.1, 130.7, 132.0, 133.5, 136.2, 140.2, 147.7,
159.6, 176.5, 177.0. IR (KBr) 3408, 1708, 1687 cm-1. Anal.
Calcd for C24H32N2O3 (396.53): C, 72.70; H, 8.13; N, 7.04.
Found: C, 72.54; H, 8.24; N, 6.98.
2-Eth yl-2-(3-(2-Am in oph en yl)-2-pyr idyl)bu tan -1-ol (33).
The same procedure as for the synthesis of 15a was applied
to pivalamide 30 (168 mg, 0.47 mmol). Chromatography (1:2
EtOAc/petroleum ether) yielded 33 (91 mg, 72%) as a white
solid, mp 139 °C. 1H NMR (300 MHz, CDCl3) δ 0.65 (t, J )
7.3, 6H), 1.39-1.71 (m, 4H), 3.34 (br s, 2H), 3.70 (d, J ) 11.7,
1H), 3.95 (d, J ) 11.7, 1H), 4.25 (br s, 1H), 6.69 (m, 2H), 6.94
(dd, J ) 7.7 and 1.5, 1H), 7.14 (m, 2H), 7.34 (dd, J ) 7.7 and
1.8, 1H), 8.50 (dd, J ) 4.8 and 1.8, 1H). 13C NMR (75 MHz,
CDCl3) δ 9.4, 9.6, 27.2, 28.5, 51.0, 67.0, 115.6, 117.9, 121.4,
126.5, 129.2, 130.1, 134.2, 141.7, 143.9, 147.4, 164.7. IR (KBr)
3476, 3337 cm-1. Anal. Calcd for C17H22N2O (270.38): C, 75.52;
H, 8.20; N, 10.36. Found: C, 75.89; H, 8.19; N, 10.39.
13,13-Dieth yl-10,11,12,13-tetr a h yd r o-11-oxa -9H-ben zo-
[b]p yr id o[3,2-d ]a zon in -10-on e (6). Cooled (-70 °C), ethanol-
free CH2Cl2 (2 mL) was added to a N2-flushed flask containing
amino alcohol 32 (25 mg, 0.094 mmol), 4-DMAP (105 mg. 0.94
mmol), and triphosgene (31 mg. 0.105 mmol). After 15 min of
stirring at -70 °C, the reaction mixture was allowed to warm
to room temperature over 4 h, after which it was hydrolyzed
(2 mL of aqueous K2CO3) and extracted with EtOAc. The
combined organic extracts were dried, and the solvent was
evaporated. The residue was subjected to chromatography
(99:1 CH2Cl2/MeOH) to yield 6 (20 mg, 70%), as an orange
solid, mp 176 °C. 1H NMR (300 MHz, CDCl3) δ 0.62 (t, J )
7.3, 3H), 0.82 (t, J ) 7.3, 3H), 1.20, 1.44-1.61, 1.80, 2.08 (4m,
4H), 3.78 (d, J ) 11.0, 1H), 4.27 (d, J ) 11.0, 1H), 6.05 (br s,
1H), 7.08 (m, 3H), 7.20 (m, 2H), 7.29 (m, 1H), 8.58 (dd, J )
4.1 and 2.2, 1H). 13C NMR (75 MHz, CDCl3) δ 8.3, 8.4, 23.4,
24.2, 52.1, 73.1, 120.9, 125.4, 126.0, 128.6, 129.9, 135.3, 136.6,
140.2, 141.7, 148.5, 156.6, 160.0. IR (KBr) 1714 cm-1. MS (CI,
t-BuH) m/z 297 (M + H)+. Anal. Calcd for C18H20N2O2
(296.37): C, 72.95; H, 6.80; N, 9.45. Found: C, 72.77; H, 6.82;
N, 9.41.
13,13-Dieth yl-10,11,12,13-tetr ah ydr o-9H-ben zo[b]pyr ido-
[3,2-d ]a zon in -10-on e (5d ). The same procedure as for the
synthesis of 5a was applied to amino acid 25b (69 mg, 0.22
mmol), the reaction mixture (solvent: CHCl3) being heated at
50 °C for 36 h with introduction of an additional 0.5 equiv of
HOBT/EDCI/NEt3 after 24 h. The solvent was evaporated and
the residue chromatographed (96:4 CH2Cl2/MeOH) to yield 5d
(62 mg, 95%), as a pale brown solid, mp 172 °C.1H NMR (300
MHz, CDCl3, 50 °C) δ 0.44 (t, J ) 7.3, 3H), 0.69 (t, J ) 7.3,
3H), 1.21 (m, 2H), 1.66 (m, 2H), 1.78, 2.07-2.57 (2m, 4H), 6.63
(br s, 1H), 6.99 (dd, J ) 7.6 and 4.8, 1H), 7.08 (dd, J ) 7.6 and
2.0, 1H), 7.17 (m, 1H), 7.32 (m, 3H), 8.53 (m, 1H). 13C NMR
(100 MHz, CDCl3) δ 7.1, 7.3, 28.7 (this chemical shift corre-
sponds to the midpoint of a very broad signal), 30.2, 47.6, 52.5,
119.2, 126.8, 127.0, 128.0, 128.4, 132.9, 134.5, 137.4, 141.8,
146.8, 161.1, 174.8. IR (KBr) 1653 cm-1. MS (CI, t-BuH) m/z
295 (M + H)+. Anal. Calcd for C19H22N2O (294.40): C, 77.52;
H, 7.53; N, 9.52. Found: C, 77.21; H, 7.50; N, 9.51.
13-Meth yl-13-vin yl-10,11,12,13-tetr a h yd r o-9H-ben zo[b]-
p yr id o[3,2-d ]a zon in -10-on e (5e). The same procedure as for
the synthesis of 5a was applied to amino acid 26 (36 mg, 0.12
mmol), the reaction mixture (solvent: CHCl3) being refluxed
for 40 h with introduction of an additional 0.5 equiv of HOBT/
EDCI/NEt3 after 24 h. The solvent was evaporated and the
residue chromatographed (93:7 CH2Cl2/MeOH) to yield 5e (27
mg, 80%), as a white solid (3:1 mixture of diastereoisomers).
1H NMR (300 MHz, CDCl3, 40 °C) δ 1. 00 (s, 0.75H), 1.48 (s,
2.25H), 1.62-2.51 (m, 4H), 4.50 (d, J ) 17.6, 0.75H), 4.51 (d,
J ) 11.0, 0.75H), 4.96 (d, J ) 17.6, 0.25H), 5.06 (d, J ) 11.0,
0.25H), 5.72 (dd, J ) 17.6 and 11.0, 0.75H), 6.59 (m, 0.25H),
6.78 (br s, 0.75H), 6.91 (br s, 0.25H), 7.04 (m, 1H), 7.11-7.39
(m, 5H), 8.54 (m, 1H). 13C NMR (Problems of relaxation affect
the signals and some of them are missing, even with a D1
parameter of several minutes.) (75 MHz, CDCl3) δ 48.7, 110.5,
120.9, 127.8, 128.0, 128.5, 129.3, 134.1, 138.1, 138.4, 142.3,
148.6. IR (KBr) 1669 cm-1. MS (CI, t-BuH) m/z 279 (M + H)+.
Anal. Calcd for C18H18N2O (278.36): C, 77.67; H, 6.52; N, 10.06.
Found: C, 77.85; H, 6.55; N, 10.05. Diastereoisomers were
separated by semipreparative HPLC. mps: 168 °C (major
diastereoisomer) and 210 °C (minor diastereoisomer).
Eth yl 2-Eth yl-2-(3-(2-p iva la m id op h en yl)-2-p yr id yl)bu -
ta n oa te (29). To a solution of diisopropylamine (0.29 mL, 2.05
mmol) in THF (5 mL) was added n-BuLi (0.82 mL, 2.05 mmol)
at -70 °C. The reaction mixture was stirred for 15 min at -70
°C before adding a solution of ester 28 (170 mg, 0.5 mmol) in
THF (3 mL). After 30 min of stirring, iodoethane (0.39 mL,
2.5 mmol) was added. The reaction mixture was allowed to
warm to room temperature over 3 h after which it was
hydrolyzed (5 mL of water) and extracted with CH2Cl2. The
combined organic extracts were dried, and the solvent was
evaporated. The crude residue was eluted through a short plug
of silica gel (1:3 EtOAc/petroleum ether) and then submitted
to another sequence of metalation-ethylation, using the same
conditions as above. After usual workup, the residue was
Ack n ow led gm en t. We wish to acknowledge Dr.
Claude Thal who encouraged this research. We also
thank the contribution of Sylviane Thoret and Chris-
tiane Gaspard for the biological assays.
Su p p or tin g In for m a tion Ava ila ble: Compounds 8-11,
14-17, 19-22, 23c,d , 27, 28, and 30-32 are described in this
section. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O0014156