Pyridoxine-derived bicyclic aminopyridinol antioxidants: Synthesis and their antioxidant activities

Article abstract of DOI:10.1039/c1ob05144j

A few facile synthetic pathways for bicyclic aminopyridinol antioxidants are presented. Attachment of a long alkyl chain to the bicyclic pyridinol scaffold was established using ester linkage. Non-substituted pyrrolopyridinols and 1,3-oxazine-fused pyridinols were also synthesized as novel antioxidant scaffolds. Antioxidant activities were measured by a radical clock method and new compounds prepared are comparable to the best bicyclic aminopyridinol antioxidants. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1ob05144j

View Article Online / Journal Homepage / Table of Contents for this issue
Organic &
Biomolecular
Chemistry
Dynamic Article Links
Cite this: Org. Biomol. Chem., 2011, 9, 8475
www.rsc.org/obc
PAPER
Pyridoxine-derived bicyclic aminopyridinol antioxidants: synthesis and their
antioxidant activities†
Tae-gyu Nam,a,b Jin-Mo Ku,c Christopher L. Rector,a Hoyoung Choi,d Ned A. Porter*a and
Byeong-Seon Jeong*d
Received 27th January 2011, Accepted 22nd September 2011
DOI: 10.1039/c1ob05144j
A few facile synthetic pathways for bicyclic aminopyridinol antioxidants are presented. Attachment of
a long alkyl chain to the bicyclic pyridinol scaffold was established using ester linkage. Non-substituted
pyrrolopyridinols and 1,3-oxazine-fused pyridinols were also synthesized as novel antioxidant scaffolds.
Antioxidant activities were measured by a radical clock method and new compounds prepared are
comparable to the best bicyclic aminopyridinol antioxidants.
than bicyclic analogues, but the former are still excellent chain-
breaking antioxidants. Many of these compounds have antiox-
idant activity several times better than a-TOH.2g In addition,
Introduction
Since the introduction of mono- and bicyclic aminopyridinol
antioxidants which typically possess better antioxidant activity
some monocyclic derivatives are such good co-antioxidants that
than a-tocopherol (a-TOH), nature’s most active chain-breaking
antioxidant,1 there have been an increasing number of synthetic
approaches to this novel scaffold (Fig. 1).2 The electronic effect
of a ring nitrogen increases the ionization potential (IP) of these
compounds and greatly improves the air-stability of aminopyridi-
nols compared to the analogous phenolic compounds. Nitrogen
ring substitution therefore addresses one of the major issues in the
development of potent antioxidants.3
they can spare co-existing endogenous antioxidants such as uric
acid to maximize the protective effect against oxidative stress.2j
Among the bicyclic aminopyridinols are a group of derivatives
that have lipophilic side chains. These hydrophobic analogues
showed significantly superior antioxidant properties to a-TOH
in that (i) they have 10–80 times higher rate constant (kinh) for
inhibition of the radical chain reaction, (ii) they spare endogenous
a-TOH from consumption, and (iii) they do not propagate a-
TOH-mediated peroxidation processes.2c Importantly, the most
advanced analogue of this kind, N-TOH (B6, R1 = R2 = Me, R3 =
C16*), showed further characteristics which could render it a good
in vivo antioxidant.2d It was suggested that N-TOH can diffuse
1.5-times faster than a-TOH to the site of a lipid peroxyl radical
in a biological membrane, and that it binds better than a-TOH to
the tocopherol transfer protein (hTTP).2d
We have recently reported a significantly improved synthetic
pathway to the aminopyridinols where pyridoxine·HCl (1, one
of the constituents of vitamin B6) is the starting material (Fig.
2). As a result, bicyclic aminopyridinols, such as naphthyridinol
22j and pyrrolopyridinol 3,2k were easily synthesized in large
quantity starting from 1. In addition, a new series of monocyclic
analogue 42j was derived from 1. In the current study, we
report on the preparation of another series from this versatile
antioxidant scaffold. We describe here the synthesis of various
types of pyridoxine-derived bicyclic aminopyridinols along with
their antioxidant activities.
Fig.
1
Structures of a-tocopherol and mono- and bicyclic
aminopyridinols.
Various modifications on the aminopyridinol scaffold have
been made and relevant synthetic methods developed. In general,
monocyclic aminopyridinols showed weaker antioxidant activities
aDepartment of Chemistry, Vanderbilt University, Nashville, Tennessee,
37235, USA. E-mail: n.porter@vanderbilt.edu; Fax: +1-615-343-5478;
Tel: +1-615-343-2693
bCollege of Pharmacy, Hanyang University, Ansan, 426-791, Republic of
Korea
cGyeonggi Bio-Center, Suwon, 443-270, Republic of Korea
Results and discussion
dCollege of Pharmacy, Yeungnam University, Gyeongsan, 712-749, Republic
of Korea. E-mail: jeongb@ynu.ac.kr; Fax: +82-53-810-4654; Tel: +82-53-
810-2814
Antioxidant activities of phenolic compounds are largely depen-
dent on the degree of orbital overlap between the oxygen radical
center and the lone-pair orbital of a para-substituted heteroatom.3a
† Electronic supplementary information (ESI) available: 1H, 13C NMR
spectra of all new compounds. See DOI: 10.1039/c1ob05144j
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8475–8482 | 8475
©

View Article Online
Fig. 2 Pyridoxine·HCl, a highly efficient natural source for aminopyridi-
nols (R1, R2, R3, R4 = H or alkyl group).
Scheme 1 Reagents and conditions (a) CH3CHO, AcOH, NaBH3CN,
MeOH, rt, 2 h, 84%; (b) DIBAL-H, CH2Cl2, 0 ◦C, 4 h, 92%; (c) Ac2O,
pyridine, DMAP, rt, 0.5 h, 96%; (d) H2, Pd/C, MeOH, rt, 3 h, 93%.
Therefore, the activity can be modulated by the pattern of the
substituents attached to the para-substituted heteroatom since
this substitution can determine the degree of orbital overlap. For
example, better antioxidant activities of bicyclic compounds than
their monocyclic analogues in both the phenol and aminopyridinol
series has been attributed to the favorable orbital overlap due to
the stereoelectronic effect of the bicyclic geometry. Furthermore,
within the bicyclic aminopyridinol system, it has been reported
that the geometry of five-membered pyrrolidine-fused system B5
is more favorable for orbital overlap than that of the six-membered
piperidine-fused system B6. The improved overlap results in a two
to three-fold better antioxidant activity for pyrrolidines than is
observed for the piperidines.1b
intermediate 5, we have developed and reported a high-yielding
synthesis starting from pyridoxine·HCl (1).2k The NH group of 5
was ethylated by reductive alkylation for solubility reason to give 6
in 84% yield. Unlike the substitution at the C(᭜)-position, N-alkyl
substitution (N-ethyl vs. N-methyl) would not have significant
stereoelectronic effect on antioxidant activity. t-Butyl ester group
of 6 was reduced to alcohol 7 with DIBAL-H in 92% yield. The
alcohol group in 7 was then acetylated to afford 8 (96%) where
R = CH3 is a representative fatty acid (RCO2H). A lipophilic side
chain in the form of an O-acyl group should provide solubility in
bulk solvents. Catalytic hydrogenolysis removed benzyl group to
give the dialkyl model compound 9 in 93% yield.
While substitutions at para-position dramatically alter this
orbital overlap, substitutions on the a-carbon (i.e., C(᭜)-position
in B6) to the para-nitrogen do not seem to significantly modify the
stereoelectronic effect in the aminopyridinol system. In piperidine-
fused aminopyridinols B6, the antioxidant activities, reflected in
Next, in order to compare the stereoelectronic effect, 16 having
no alkyl substitution at C(᭜)-position was synthesized (Scheme 2).
k
inh, vary only <20% depending on R2 and R3 groups.2d On the
other hand, it is well documented that the stereochemistry of
the quaternary carbon center in a-TOH (equivalent to C(᭜)-
position in B6) where C16*-chain is attached to chromanol system
is important for its in vivo activity4 because it is crucial for the
binding affinity of a-TOH to hTTP. It is, of course, uncertain that
a C16-isoprenoid chain will lead to the maximal activity for the
aminopyridinols. For example, a class of bicyclic aminopyridinol
B6 (R1 = CH2(CH2)14CH3, R2 = R3 = H) with a simple linear
C16-chain connected to piperidine ring nitrogen rather than to
the C(᭜)-position also showed excellent antioxidant activities.
Although this compound remains untested on its binding affinity
to hTTP, it spared endogenous a-TOH and did not promote
tocopherol-mediated lipid peroxidation in an isolated human LDL
particle.2c
We have first explored the possibility that we can attach a
lipophilic side chain in a way to avoid a long synthetic procedure
for the C16-isoprenoid unit (C16*). To this end, a fatty acid
(RCO2H) was attached to bicyclic system via a simple esterification
(Scheme 1). This neopentyl-type ester bond in 9 should be stable
toward hydrolysis, thereby providing lipophilicity in cellular and
physiological environments. As shown in Scheme 1, by putting an
acetyl group as a representative acyl group, we have demonstrated
that we can easily elongate the lipophilic moiety of 9. As for the
Scheme 2 Reagents and conditions (a) KCN, acetone-H2O, reflux, 1 h,
98%; (b) KOH, EtOH, reflux, 12 h, 88%; (c) BH3-THF, THF, reflux, 12 h,
40%; (d) CuOAc, K3PO4, diethyl salicylamide, DMF, 40 ◦C, 15 h; (e)
CH3CHO, AcOH, NaBH3CN, MeOH, rt, 2 h, 63% for two steps; (f) H2,
Pd/C, MeOH, 3 h, rt, 93%.
8476 | Org. Biomol. Chem., 2011, 9, 8475–8482
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Although the synthesis of N-methyl version of 16 was already
reported using 2-nitro-m-xylene as an oxygenating agent,1b,2a we
report here a new synthesis of 16 starting from pyridoxine·HCl
(1). We chose to prepare the bicyclic aminopyridinol 16 containing
the N-ethyl group for better solubility and structural homology to
aminopyridinol 9. Displacement of chloride in 10, which could
be readily prepared from pyridoxine·HCl (1) according to the
synthetic method developed by us,2k from the nucleophilic cyanide
anion in refluxing wet acetone to give 11 in 98% yield. Hydrolysis
of the nitrile group in 11 with ethanolic KOH solution under
reflux conditions afforded the primary amide 12 in 88% yield. The
primary amine 13 could be prepared by borane reduction of 12
in refluxing THF but only a modest yield (40%) was obtained.
Pyrrolidine ring formation was accomplished by intramolecular
Cu(I)-catalyzed amination of 13 to give 14, and the reductive
ethylation that followed afforded 15 in overall 63% yield for these
two steps. The benzyl protecting group in 15 was finally removed
by hydrogenolysis to give the C(᭜)-unsubstituted pyrrolopyridinol
16 in 93% yield. We found that 16 was unstable in air as suggested
by its N-methyl analogue;1b about 7% of 16 was found to be
rearomatized to 17 after several days. It clearly demonstrates
its susceptibility toward benzylic oxidation/aromatization pre-
sumably through an electron transfer to molecular oxygen. The
ionization potential (IP) of the N-methyl analogue was reported to
be 152.3 kcal mol-1,1b low enough to react with molecular oxygen.
N-Ethyl substitution in 16 should not change its IP significantly.
Our investigations of the stereoelectronic effect were extended
in scope to consider 1,3-oxazine-annulated pyridinol 23 as a model
structure to study the effect of the oxygen atom at the C(5¢)-
position on the orbital overlap between the pyridinoxyl radical and
the para-substituted nitrogen atom (Scheme 3). Although a C(5¢)-
oxygen could not provide a direct electron donating effect on the
aromatic ring, it still can exert stereoelectronic effect in structure
23. For maximum orbital overlap, the lone pair of the para-
nitrogen atom should be oriented perpendicular to the aromatic
ring plane (q = 0)3a,5 and this orbital overlap can be dramatically
increased by bicyclic geometry. We envisioned that this favorable
geometry could be easily induced by the N,O-ketal structure
shown in 23 and it could serve as an attractive antioxidant scaffold
to the tetrahydro-1,8-naphthyridinols B6 because of the simpler
synthetic approaches and the readily available starting material,
4-deoxypyridoxine·HCl (18)2j which in turn can be prepared from
pyridoxine·HCl (1) in high yield. It turns out to be very convenient
to install the quaternary substitution at C(᭜)-position in the
structure 23.
Scheme 3 Reagents and conditions (a) PhNH2, HCl, NaNO2, NaOH,
H2O, 0 ◦C to rt, 1 h, 95%; (b) H2, Pd/C, MeOH, rt, 6 h, 90%; (c) (i)
Ac2O, HCO2H, 60 ◦C, 20 min then 19, rt, 40 min, (ii) K2CO3, MeOH,
0
◦C, 30 min, 68% for two steps; (d) BH3–THF, THF, reflux, 4 h, 88%; (e)
(MeO)2CMe2, p-TsOH, DMSO, rt, 20 h, 70%; (f) (MeO)2CMe2, p-TsOH,
DMSO, rt, 20 h, 58%; (g) 2-hexanone, camphorsulfonic acid, DMSO, rt,
24 h, 44%; (h) n-C7H15CHO, NaBH(OAc)3, AcOH, MeOH, rt, 3 h, 73%.
Antioxidant activities of selected compounds are shown in
Table 1. The inhibition rate constants (kinh) of the aminopyridinols,
which correspond to the rate constant for H-atom transfer to
the chain-carrying peroxyl radicals in lipid peroxidation, were
measured by a peroxyl radical clock system based on the autox-
idation of pentafluorobenzyl 13(S)-hydroxyoctadeca-6Z,9Z,11E-
trienoate (PFB-13-HOTrE) (Fig. 3). This radical clock is similar
to the linoleate peroxyl radical clocks previously described,
but relies on the assistance of mass spectrometry for product
analysis.7 This clock is based on the competition between trapping
the kinetically favored 8-hydroperoxy, 13(S)-6Z,9Z,11E-trienoate
(8,13-c,c,t) versus peroxyl radical b-fragmentation that leads to
other thermodynamically more stable products. This system gives
good values of kinh as has been established with antioxidants having
known kinh values.
For the synthesis of 23 (Scheme 3), 18 was coupled with
diazotized aniline, then, the diazo group of 19 was reduced
under catalytic hydrogenation conditions to form 6-amino-4-
deoxypyridoxine (20) in 86% for two steps. Triformylation of
20 by acetic formic anhydride/formic acid followed by selective
hydrolysis afforded the 6-formamido derivative 21 in 68% yield
for two steps. The formamido group of 21 was reduced with
borane-THF complex to give the N-methyl product 22 in 88%
yield. Subsequent N,O-ketalization with 2,2-dimethoxypropane
and 2-hexanone gave 23a (70% from 20), 23b and 23c (58% and
44% from 22), respectively. Monocyclic derivative 24 was also
prepared from 22 to examine the effects of the structural difference
between monocyclic and bicyclic systems on the antioxidant
activity.
Table 1 Rate constants (kinh) measured by PFB-13-HOTrE radical
clocka,6
Compounds
kinh (107 M-1s-1)
kinh/kinh(a-TOH)
a-TOH
9
0.35
1.0
3.95 0.72
3.79 0.65
3.07 0.47
1.60 0.19
5.20 0.78
11.3
10.8
8.8
4.6
14.9
16
23c
24
25b
a See experimental section for details. b 25 was prepared by the reported
procedure,2d where its kinh was reported.
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8475–8482 | 8477
©

View Article Online
Experimental
General
Unless noted otherwise, materials were purchased from com-
mercial suppliers and used without further purification. Air- or
moisture-sensitive reactions were carried out under an inert gas
atmosphere. THF and CH2Cl2 were dried using a Solvent Purifi-
cation System from Solvtek. Progress of reaction was monitored
by thin-layer chromatography (TLC) using silica gel F254 plates.
Purification of the products was performed by flash column
chromatography using silica gel 60 (230–400 mesh) or a Biotage
SP-1 system with indicated solvents. IR spectra were recorded
on a Perkin Elmer Spectrum GX FT-IR spectrometer. NMR
spectra were taken with a 300 MHz Bruker NMR spectrometer.
Chemical shifts (d) were expressed in ppm using solvent as an
internal standard and coupling constant (J) in hertz. Melting
points were taken on a Fischer-Jones melting point apparatus
and are uncorrected. Low-resolution mass spectra (MS) were
recorded on a Agilent Technologies Quadruple 6130 LC/MS.
High-resolution mass spectra (HRMS) were recorded using the
electrospray technique. ES-HRMS measurement were performed
at Ohio State University.
Fig. 3 The PFB-13-HOTrE radical clock.
The compound 23c is a slightly poorer H-atom donor than
the tetrahydro-1,8-naphthyridin-3-ol analogue 25. Oxygen sub-
stitution at the 3-position and bulky dialkyl substitution (C(᭜)-
methylbutyl) in 23c possibly decreases orbital overlap by distorting
molecular geometry. On the other hand, 23c showed about two-
fold higher kinh than its monocyclic counterpart 24, confirming
the notion of a favorable stereoelectronic effect. Although 24
possibly mimics the bicyclic geometry through a intramolecular
hydrogen bond between the free OH group and para-nitrogen,
the conformational analogy, if any, did not contribute to the
antioxidant activity. Indeed, it is likely that an intramolecular
hydrogen bond would be at the expense of the lone pair electron
of the para-nitrogen and cause a larger dihedral angle (q) to the
pyridinoxyl radical. It is noteworthy, however, that the monocycle
24 and the bicycle 23c are 5- and 10-fold better antioxidants than
a-TOH, respectively, demonstrating the novelty of the scaffold.
Pyrrolopyridinols 9 and 16 showed interesting antioxidant
activities. First, C(᭜)-dialkylated 9 and non-alkylated 16 have
similar kinh. It suggested that both stereoelectronic and direct
electron donating effect of C(᭜)-substitution is less important
in pyrrolopyridinol scaffold. Second, it seems that the ester
linkage in 9 does not significantly perturb kinh, demonstrating
the usefulness of this elongation strategy. Finally, five-membered
ring-fused pyrrolopyridinols appear to have less favorable orbital
overlap compared to the six-membered ring-fused tetrahydro-1,8-
naphthyridinols than we has been previously expecting.1b In fact,
the (9 and 16) rate constants (kinh) lie in close range to that of the
representative tetrahydro-1,8-naphthyridinol 25.
tert-Butyl 5-benzyloxy-1-ethyl-2,4,6-trimethyl-2,3-dihydro-1H-
pyrrolo[2,3-b]pyridine-2-carboxylate (6). To a solution of 5 (720
mg, 1.95 mmol) in methanol (20 mL) were added acetaldehyde
(1.1 mL, 19.5 mmol) and acetic acid (0.56 mL, 9.75 mmol). After
addition of sodium cyanoborohydride (613 mg, 9.75 mmol), the
reaction mixture was stirred for 2 h at room temperature. Methanol
was evaporated and the residue was basified with sat. Na2CO3
solution. Extraction of the mixture with EtOAc (100 mL¥2) was
performed. The combined organic solution was washed with brine,
dried over MgSO4, and concentrated. The residue was purified by
silica gel column chromatography (hexanes : EtOAc = 6 : 1) to give
6 (650 mg, 84%) as pale yellow oil. 1H NMR (300 MHz, CHCl3-d)
d 7.34–7.46 (m, 5H), 4.71 (s, 2H), 3.45–3.52 (m, 1H), 3.16–3.25
(m, 2H), 2.79 (d, 1H, J = 16.2 Hz), 2.39 (s, 3H), 2.08 (s, 3H), 1.52
(s, 3H), 1.43 (s, 9H), 1.27 (t, 3H, J = 7.2 Hz); 13C NMR (75 MHz,
CHCl3-d) d 173.7, 157.7, 146.9, 144.1, 137.6, 135.4, 128.4, 127.9,
117.1, 81.3, 75.0, 69.2, 38.6, 37.5, 27.9, 22.8, 19.2, 15.0, 12.6; IR
(KBr) n 2975, 2930, 1726, 1620, 1585, 1475, 1368, 1268, 1211,
1156, 1116, 1096, 1037, 1013, 846, 733, 697 cm-1; MS (ESI+): m/z
397.3 [M+H]+; HRMS calcd for C24H32N2O3 [M+H]+ 397.2492,
found 397.2492.
(5-Benzyloxy-1-ethyl-2,4,6-trimethyl-2,3-dihydro-1H-pyrrolo-
[2,3-b]pyridin-2-yl)methanol (7). To a cooled (0 ◦C) solution of 6
(570 mg, 1.44 mmol) in anhydrous CH2Cl2 (20 mL) was added 1 M
DIBAL-H in THF (1.58 mL, 1.58 mmol). After the mixture was
stirred for 4 h at 0 ◦C, the mixture was quenched with a few drops
of methanol and warmed up to room temperature. sat. Sodium
potassium tartrate solution (20 mL) was added and the mixture
was stirred for 1 h at room temperature. Extraction with CH2Cl2
(100 mL ¥ 2) was carried out and the combined extracts were dried
over MgSO4 and concentrated. The residue was purified by silica
gel column chromatography (hexanes : EtOAc◦= 2 : 1) to yield 7
(432 mg, 92%) as a pale yellow solid. m.p. 123 C; 1H NMR (300
MHz, CHCl3-d) d 7.35–7.49 (m, 5H), 4.72 (s, 2H), 3.67 (d, 1H,
J = 11.1 Hz), 3.35–3.42 (m, 2H), 3.18–3.25 (m, 1H), 3.12 (d, 1H,
Conclusions
A facile approach to attach an alkyl chain to the pyrrolopyridinol
antioxidants has been developed. Methods reported can be applied
to the synthesis of the tetrahydro-1,8-naphthyridinol scaffold as
well. In addition, we have introduced the synthesis of C(᭜)-
non substituted pyrrolopyridinols and 1,3-oxazine-fused series
of bicyclic aminopyridinols as novel antioxidant scaffolds. These
facile synthetic pathways and their excellent antioxidant activities
demonstrate the versatility of the synthetic approaches and the
possible range of application of these antioxidants.
8478 | Org. Biomol. Chem., 2011, 9, 8475–8482
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
J = 16.2 Hz), 2.56 (d, 1H, J = 16.2 Hz), 2.40 (s, 3H), 2.11 (s, 3H),
1.29 (t, 3H, J = 7.2 Hz); 1.18 (s, 3H); 13C NMR (75 MHz, CHCl3-
d) d 157.8, 146.8, 144.5, 137.5, 136.1, 128.5, 127.9, 127.8, 118.1,
75.0, 66.7, 66.5, 35.5, 35.2, 21.4, 19.2, 15.3, 12.7; IR (KBr) n 3386,
3032, 2965, 2927, 2868, 1623, 1579, 1486, 1433, 1399, 1367, 1215,
1095, 1049, 989, 739, 697 cm-1; MS (ESI+): m/z 327.2 [M+H]+;
HRMS calcd for C20H26N2O2 [M+H]+ 327.2073, found 327.2074.
(KBr) n 3032, 2923, 2253, 1575, 1497, 1440, 1408, 1366, 1249 m,
1215, 1189, 1086, 965, 935, 910, 757, 700 cm-1; MS (ESI+): m/z
331.0 [M+H]+; HRMS calcd for C16H16BrN2O [M+H]+ 331.0446,
found 331.0443.
2-(3-Benzyloxy-6-bromo-2,4-dimethylpyridin-5-yl)acetamide
(12). To a solution of 11 (1.0 g, 3.02 mmol) in ethanol (40 mL)
was added potassium hydroxide (997 mg, 15.10 mmol) and the
resulting mixture was refluxed for 12 h. After concentration of
the mixture, the residue was diluted with water (20 mL) and
extracted with chloroform (30 mL¥3). The combined extracts
were dried over MgSO4 and concentrated to afford 12 (928 mg,
88%) as a yellow solid. For analytical sample, silica gel column
chromatography (CHCl3 : MeOH = 20 : 1) was carried out to give
a light yellow solid. m.p. 191–195 ◦C; 1H NMR (300 MHz, DMSO-
d6) d 7.38–7.50 (m, 6H), 7.05 (s, 1H), 4.82 (s, 2H), 3.63 (s, 2H),
2.37 (s, 3H), 2.24 (s, 3H); 13C NMR (75 MHz, DMSO-d6) d
170.2, 151.5, 151.1, 143.5, 138.4, 137.0, 131.2, 128.8, 128.7, 128.6,
74.7, 39.0, 19.2, 13.8; IR (KBr) n 3375, 3197, 2922, 1667, 1618,
1399, 1363, 1247, 1218, 1183, 1095, 977, 939, 841, 730, 695 cm-1;
MS (ESI+): m/z 349.0 [M+H]+; HRMS calcd for C16H18BrN2O2
[M+H]+ 349.0552, found 349.0539.
(5-Benzyloxy-1-ethyl-2,4,6-trimethyl-2,3-dihydro-1H-pyrrolo-
[2,3-b]pyridin-2-yl)methyl acetate (8). To
a solution of 7
(223 mg, 0.68 mmol) in pyridine (3 mL) was added 4-
dimethylaminopyridine (17 mg, 0.14 mmol) and acetic anhydride
(77 mL, 0.82 mmol) at room temperature. After the mixture was
stirred for 30 min at room temperature, the mixture was diluted
with EtOAc (200 mL) and successively washed with water (50 mL)
and brine (50 mL). The EtOAc solution was dried over MgSO4
and concentrated. The residue was purified by silica gel column
chromatography (hexanes : EtOAc = 3 : 1) to yield 8 (240 mg, 96%)
1
as a pale yellow oil. H NMR (300 MHz, CHCl3-d) d 7.32–7.50
(m, 5H), 4.71 (s, 2H), 4.07 (dd, 2H, J = 15.8, 11.4 Hz), 3.33 (q,
2H, J = 8.1 Hz), 2.94 (d, 1H, J = 16.2 Hz), 2.67 (d, 1H, J = 16.2
Hz), 2.39 (s, 3H), 2.09 (s, 3H), 2.02 (s, 3H), 1.30 (s, 3H); 1.23 (t,
3H, J = 8.1 Hz); 13C NMR (75 MHz, CHCl3-d) d 170.9, 157.3,
146.7, 143.9, 137.6, 135.7, 128.5, 127.9, 127.8, 117.3, 75.0, 68.4,
64.2, 36.8, 35.4, 22.2, 20.8, 19.2, 15.3, 12.6; IR (KBr) n 3031, 2967,
2928, 1743, 1620, 1582, 1477, 1429, 1398, 1371, 1324, 1224, 1094,
1040, 990, 725, 730 cm-1; MS (ESI+): m/z 369.2 [M+H]+; HRMS
calcd for C22H28N2O3 [M+H]+ 369.2178, found 369.2170.
5-Aminoethyl-3-benzyloxy-6-bromo-2,4-dimethylpyridine (13).
To a suspension of 12 (500 mg, 1.43 mmol) in dry THF (10 mL) was
added BH3-THF complex (1.0 M in THF, 5.72 mL, 5.72 mmol) at
room temperature. The reaction mixture was refluxed for 12 h and
cooled down to room temperature. After quenching the reaction
mixture with a few drops of water, sat. NaHCO3 solution was
added to the mixture. The resulting mixture was stirred for 10 min
and extracted with EtOAc (50 mL¥3). The combined extracts
were washed with brine and dried over MgSO4. After filtration
and concentration, the residue was purified over silica gel column
chromatography (CH2Cl2 : MeOH = 20 : 1) to afford 13 (192 mg,
40%) as a sticky caramel. 1H NMR (300 MHz, CHCl3-d) d 7.35 (s,
5H), 4.74 (s, 2H), 3.67 (br s, 2H), 2.90–3.09 (m, 4H), 2,42 (s, 3H),
2.21 (s, 3H); 13C NMR (75 MHz, CHCl3-d) d 152.9, 152.4, 142.8,
138.4, 136.4, 131.1, 129.1(¥2), 129.0(¥2), 128.5, 75.5, 47.4, 32.0,
19.8, 13.8; IR (KBr) n 3360, 3032, 2925, 2871, 1729, 1574, 1454,
1401, 1367, 1249, 1215, 1124, 950, 738, 698 cm-1; MS (ESI+): m/z
335.1 [M+H]+; HRMS calcd for C16H20BrN2O [M+H]+ 335.0759,
found 335.0751.
(1-Ethyl-5-hydroxy-2,4,6-trimethyl-2,3-dihydro-1H-pyrrolo[2,3-
b]pyridin-2-yl)methyl acetate (9). To a solution of 8 (125 mg, 0.34
mmol) in methanol (5 mL) was added palladium (10% on activated
carbon, 10 mg). The mixture was stirred with hydrogen balloon
for 3 h at room temperature. The solid in the reaction mixture was
filtered through Celite pad and the filtrated was filtered again with
R
syringe filter (Advantecꢀ JP050AN). The filtrate was concentrated
to give 9 (88 mg, 93%) as a pale yellow oil. 1H NMR (300 MHz,
DMSO-d6) d 7.36 (s, 1H), 3.99 (dd, 2H, J = 30.9, 11.1 Hz), 3.15
(q, 2H, J = 6.9 Hz), 2.82 (d, 2H, J = 15.9 Hz), 2.55 (d, 2H, J = 15.9
Hz), 2.17 (s, 3H), 1.97 (s, 3H), 1.94 (s, 3H), 1.17 (s, 3H); 1.08 (t,
3H, J = 6.9 Hz); 13C NMR (75 MHz, DMSO-d6) d 170.7, 155.2,
141.2, 140.4, 132.3, 117.2, 68.0, 64.3, 36.6, 35.4, 21.9, 21.0, 19.8,
15.7, 13.0; IR (KBr) n 3392, 2971, 2932, 1741, 1669, 1585, 1431,
1377, 1353, 1323, 1232, 1095, 1044, 991, 752 cm-1; MS (ESI+): m/z
279.2 [M+H]+; HRMS calcd for C15H22N2O3 [M+H]+ 279.1709,
found 279.1704.
5-Benzyloxy-1-ethyl-4,6-dimethyl-2,3-dihydro-1H-pyrrolo[2,3-
b]pyridine (15). To a mixture of copper(I) acetate (2.2 mg,
0.018 mmol), N,N-diethylsalicylamide (14 mg, 0.072 mmol) and
potassium phosphate tribasic (153 mg, 0.72 mmol) was added a
solution of 13 (120 mg, 0.36 mmol) in dry DMF (4 mL). After the
reaction mixture was stirred for 15 h at 40 ◦C, 1 M NaOH (1 mL)
was added to the mixture. The mixture was diluted with EtOAc
(100 mL) and water (10 mL) and the organic layer was washed
with water (10 mL¥4). The organic layer was dried over MgSO4
and concentrated to afford crude 14.
The crude 14 was dissolved in methanol (10 mL) were added
acetaldehyde (0.2 mL, 3.60 mmol) and acetic acid (0.1 mL,
1.80 mmol). After addition of sodium cyanoborohydride (113 mg,
1.80 mmol), the reaction mixture was stirred for 2 h at room
temperature. Methanol was evaporated and the residue was
basified with sat. Na2CO3 solution. After extraction of the mixture
with EtOAc (50 mL¥2), the combined organic solution was washed
3-Benzyloxy-6-bromo-5-cyanomethyl-2,4-dimethylpyridine (11).
To a suspension of 10 (300 mg, 0.796 mmol) in acetone (2.5 mL)
was added a solution of potassium cyanide (363 mg, 5.568 mmol)
in water (2 mL). The reaction mixture was refluxed for 1 h. The
mixture was diluted with chloroform (30 mL) and water (5 mL)
and the aqueous layer was extracted with chloroform (20 mL¥2).
The organic solution was washed with brine and dried over MgSO4
and concentrated. The residue was purified by silica gel column
chromatography (hexanes : EtOA◦c = 4 : 1) to give 11 (258 mg, 98%)
as a light yellow solid. m.p. 87–88 C; 1H NMR (300 MHz, CHCl3-
d) d 7.42–7.44 (m, 5H), 4.83 (s, 2H), 3.85 (s, 2H), 2.51 (s, 3H), 2.36
(s, 3H); 13C NMR (75 MHz, CHCl3-d) d 154.2, 152.2, 142.9, 137.7,
136.3, 129.2, 129.1, 128.5, 125.3, 116.1, 75.7, 22.0, 19.9, 14.1; IR
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8475–8482 | 8479
©

View Article Online
with brine, dried over MgSO4, and concentrated. The residue was
purified by silica gel column chromatography (hexanes : EtOAc =
5 : 1) giving 15 (64 mg, 63% from 13) as a pale yellow oil. 1H NMR
(300 MHz, CHCl3-d) d 7.27–7.49 (m, 5H), 4.74 (s, 2H), 3.44 (t,
2H, J = 8.4 Hz), 3.36 (q, 2H, J = 7.2 Hz), 2.84 (t, 2H, J = 8.4
Hz), 2,38 (s, 3H), 2.11 (s, 3H), 1.19 (t, 3H, J = 7.2 Hz); 13C NMR
(75 MHz, CHCl3-d) d 152.9, 152.4, 142.8, 138.4, 136.4, 131.1,
129.1(¥2), 129.0(¥2), 128.5, 75.5, 47.4, 32.0, 19.8, 13.8; IR (KBr) n
3441, 2923, 2852, 1735, 1581, 1495, 1456, 1354, 1252, 1216, 1090,
731, 696 cm-1; MS (ESI+): m/z 283.2 [M+H]+; HRMS calcd for
C18H23N2O [M+H]+ 283.1810, found 283.1798.
2H), 4.77 (s, 1H), 4.35 (d, 2H, J = 4.8 Hz), 2.16 (s, 3H), 2.11 (s, 3H);
13C NMR (75 MHz, DMSO-d6) d 151.8, 142.7, 141.4, 135.2, 116.5,
56.9, 19.5, 12.1; IR (KBr) n 3446, 3380, 2922, 2848, 1618, 1592,
1566, 1382, 1307, 1241, 1134, 1005, 774 cm-1; MS (ESI+): m/z
169.1 [M+H]+; HRMS: calcd for C8H12N2O2 [M+H]+ 169.0972,
found 169.0974.
N-(5-Hydroxy-3-(hydroxymethyl)-4,6-dimethylpyridin-2-
yl)formamide (21)
21-1. 6-Formamido-5-((formyloxy)methyl)-2,4-dimethylpyri-
din-3-yl formate (21-1). To formic acid (8.96 mL, 237.6 mmol)
was added acetic anhydride (22.4 mL, 237.6 mmol) and the mixture
was stirred for 20 min at 60 ◦C. This mixture was cooled down to
room temperature then, 20 (5.0 g, 29.7 mmol) was added. It was
stirred for 30 min at room temperature then, 10 min at 60 ◦C. The
reaction mixture was slowly transferred to ice-cold sat. NaHCO3
solution. After 5 min stirring in ice-bath, the resulting slurry was
filtered was washed with ice-cold water. Filter cake was dried under
vacuum to give the triformyl compound 21-1. 1H NMR (300 MHz,
DMSO-d6) d 10.41 (d, 1H, J = 8.4 Hz), 9.15 (s, 1H), 8.62 (s, 1H),
8.24 (s, 1H), 5.22 (s, 2H), 2.27 (s, 3H), 2.15 (s, 3H); 13C NMR (75
MHz, DMSO-d6) d 163.3, 147.0, 143.6, 141.5, 135.7, 121.9, 56.2,
19.9, 12.2.
1-Ethyl-4,6-dimethyl-2,3-dihydro-1H-pyrrolo[2,3-b]pyridin-5-ol
(16). To a solution of 15 (55 mg, 0.19 mmol) in methanol
(1 mL) was added palladium (10% on activated carbon, 5 mg).
The mixture was stirred with hydrogen balloon for 3 h at room
temperature. The solid in the reaction mixture was filtered through
Celite pad and the filtrated was filtered again with syringe filter
R
(Advantecꢀ JP050AN). The filtrate was concentrated to give 16
(34 mg, 93%) as a pale yellow oil. 1H NMR (300 MHz, DMSO-d6)
d 7.49 (s, 1H), 3.27 (t, 2H, J = 8.1 Hz), 3.16 (q, 2H, J = 7.2 Hz),
2.74 (t, 2H, J = 8.1 Hz), 2.19 (s, 3H), 2.01 (s, 3H), 1.06 (t, 3H,
J = 7.2 Hz); 13C NMR (75 MHz, DMSO-d6) d 156.8, 141.8, 140.4,
132.4, 120.1, 50.0, 41.2, 24.7, 19.7, 13.1, 12.6; IR (KBr) n 3392,
2993, 2922, 2848, 1593, 1453, 1380, 1119, 1050, 918, 761 cm-1; MS
(ESI+): m/z 193.1 [M+H]+; HRMS calcd for C11H17N2O [M+H]+
193.1341, found 193.1340.
21-2. N -(5-Hydroxy-3-(hydroxymethyl)-4,6-dimethylpyri-
din-2-yl)formamide (21). Triformyl compound 21-1 (5.62 g, 22.3
mmol) was dissolved in dry MeOH (25 mL) into which K2CO3
(1.54 g, 11.2 mmol) was added. This reaction mixture was stirred
at 0 ◦C for 30 min. Citric acid (fine granule) was slowly added to
the reaction mixture until the pH reached 7.0. The resulting slurry
was filtered on Celite and the filter cake was completely washed
with ice-cold MeOH. Filtrate was concentrated and purified on
silica gel column chromatography (CH2Cl2 : MeOH = 15 : 1) to
5-(Hydroxymethyl)-2,4-dimethyl-6-(phenyldiazenyl)pyridin-3-ol
(19). In a beaker equipped with a mechanical stirrer and pH
electrode, 18 (3 g, 15.82 mmol) was dissolved in water (40 mL) and
cooled in an iced bath. In a separated Erlenmeyer flask, aniline
(1.59 mL, 17.40 mmol) was dissolved in 6 M HCl (15.9 mL) at
room temperature, and then cooled in iced bath. A cooled solution
of sodium nitrite (1.2 g, 17.40 mmol) in water (5 mL) was added
in small portions to the aniline solution. This diazotized aniline
solution was then added in small portions to the chilled solution
of 18. After each addition, the pH of the reaction mixture was
quickly adjusted to maintain pH 8 by addition of 2.5 M NaOH.
After the addition of the diazotized aniline solution, the reaction
mixture was allowed to warm to room temperature and stirred
for 1 h. After the reaction was completed, the mixture was placed
in an iced bath for 12 h. The solid precipitated was collected by
filtration to afford 19 (3.86 g, 95%) as a red solid. m.p. 79–80 ◦C;
1H NMR (300 MHz, CHCl3-d) d 7.13–7.36 (m, 5H), 4.83 (s, 2H),
2.38 (s, 3H), 2.09 (s, 3H); IR (KBr) n 3240, 3059, 2958, 1599, 1557,
1509, 1445, 1412, 1226, 1112, 1000, 920, 763, 735, 690 cm-1; MS
(ESI+): m/z 258.1 [M+H]+; HRMS calcd for C14H16N3O2 [M+H]+
258.1243, found 258.1225.
◦
give 21 as a pale yellow solid in 68% for two steps. m.p. 118 C;
1H NMR (300 MHz, DMSO-d6) d 9.68 (d, 1H, J = 9.6 Hz), 8.92
(d, 1H, J = 10.5 Hz), 8.48 (s, 1H), 5.10 (t, 1H, J = 5.1 Hz), 4.48
(d, 2H, J = 5.4 Hz), 2.31 (s, 3H), 2.20 (s, 3H); 13C NMR (75 MHz,
DMSO-d6) d 163.4, 147.0, 143.6, 141.6, 135.7, 121.9, 56.3, 19.9,
12.3; IR (KBr) n 3437, 2923, 2848, 1666, 1455, 1377, 1250, 1111,
810, 790 cm-1; MS (ESI+): m/z 197.0 [M+H]+; HRMS: calcd for
C9H12N2O3 [M+Na]+ 219.0746, found 219.0739.
5-(Hydroxymethyl)-2,4-dimethyl-6-(methylamino)pyridin-3-ol
(22). To a stirred solution of 21 (3.12 g, 15.9 mmol) in dry THF
(150 mL) was added BH3-THF complex (1.0 M in THF, 40.0 mL,
39.8 mmol). The reaction mixture was refluxed for 4 h and cooled
down to room temperature. MeOH (10 mL) was slowly added and
stirred for 30 min. The solvent was evaporated and the residue was
purified over silica gel column chromatography (CH2Cl2 : MeOH
= 4 : 1) to give 22 (2.55 g, 88%) as a light pink solid. m.p. 146–147
6-Amino-5-(hydroxymethyl)-2,4-dimethylpyridin-3-ol (20). To
a solution of 19 (4.0 g, 15.54 mmol) in methanol (400 mL) was
added 10% palladium on activated carbon (400 mg). The mixture
was stirred for 6 h at room temperature under H2 atmosphere
(balloon). After filtration of the reaction mixture, 80% volume of
the filtrate was evaporated to give a suspension. Et2O (200 mL)
was added to the residue and stirred for 1 h at room temperature.
The solid precipitate was collected by filtration and washed wi◦th
Et2O to give 20 (2.35 g, 90%) as a white solid. m.p. 209–210 C
(decomp.); 1H NMR (300 MHz, DMSO-d6) d 7.50 (s, 1H), 4.97 (s,
◦
1
C; H NMR (300 MHz, DMSO-d6) d 7.51 (s, 1H), 5.45 (br s,
1H), 4.85 (br s, 1H), 4.38 (s, 2H), 2.78 (s, 3H), 2.25 (s, 3H), 2.13
(s, 3H); 13C NMR (75 MHz, DMSO-d6) d 151.9, 141.6, 140.6,
135.4, 117.0, 56.5, 29.1, 19.9, 12.2; IR (KBr) n 3362, 2923, 2853,
1743, 1636, 1458, 1412, 1381, 1228, 1153, 1092, 985, 709 cm-1; MS
(ESI+): m/z 138.1 [M+H]+; HRMS: calcd for C9H14N2O2 [M+H]+
183.1128, found 183.1134.
2,2,5,7-Tetramethyl-2,4-dihydro-1H-pyrido[2,3-d][1,3]oxazin-6-
ol (23a). A mixture of 20 (45 mg, 0.45 mmol), p-toluenesulfonic
8480 | Org. Biomol. Chem., 2011, 9, 8475–8482
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
acid monohydrate (8.6 mg, 0.04 mmol), 2,2-dimethoxypropane
(6.0 mL) in dry DMSO (1.0 mL), THF (12 mL) and acetone
(3 mL) was stirred at room temperature overnight. The reaction
mixture was poured to sat. NaHCO3 solution and organic layer
was extracted with CHCl3 (6 mL¥3). The combined organic layer
was washed with water and brine, dried over anhydrous MgSO4,
concentrated under high vacuum to give 23a (66 mg, 70%). m.p.
171 C; H NMR (300 MHz, DMSO-d6) d 7.64 (br s, 1H), 6.17
(s, 1H), 4.60 (s, 2H), 2.36 (s, 3H), 1.95 (s, 3H), 1.23 (s, 6H); 13C
NMR (75 MHz, DMSO-d6) d 146.4, 142.8, 141.4, 131.5, 110.2,
81.9, 59.8, 26.7, 19.5, 11.0; IR (KBr) n 3388, 2985, 2931, 2850,
1603, 1453, 1367, 1268, 1242, 1206, 1164, 1043, 805, 737 cm-1;
MS (ESI+): m/z 209.1 [M+H]+; HRMS: calcd for C11H16N2O2
[M+H]+ 209.1285, found 209.1281.
and brine and dried over anhydrous MgSO4. After concentration,
the residue was purified on silica gel column chromatography
(hexanes : EtOAc = 4 : 1) to give 24 (995 mg, 73%) as a pale yellow
oil. 1H NMR (300 MHz, DMSO-d6) d 7.76 (s, 1H), 4.64 (s, 2H),
4.47 (dd, 1H, J = 4.5, 7.2 Hz), 3.30 (s, 2H), 2.85 (s, 3H), 2.24 (s,
3H), 1.93 (s, 3H), 1.63 (t, 2H, J = 5.1), 1.26–1.39 (m, 10H), 0.86 (t,
3H, J = 6.0 Hz); 13C NMR (75 MHz, DMSO-d6) d 147.9, 142.1,
141.9, 131.2, 113.4, 87.6, 62.6, 32.6, 31.6, 31.0, 29.3, 29.1, 24.2,
22.5, 20.0, 14.4, 11.0; IR (KBr) n 3309, 2925, 2855, 1595, 1467,
1407, 1323, 1234, 1121, 1033, 943, 769 cm-1; MS (ESI+): m/z 295.2
[M+H]+; HRMS: calcd for C17H30N2O2 [M+H]+ 295.2380, found
295.2384.
◦
1
13-HOTrE radical clock
1,2,2,5,7-Pentamethyl-2,4-dihydro-1H-pyrido[2,3-d][1,3]oxazin-
Stock solutions of PFB-13-HOTrE (1.0 M), 2,2¢-azobis(4-
methoxy-2,4-dimethylvaleronitrile) (MeO-AMVN) (0.05 M), and
antioxidant (ª0.1 M) were prepared in benzene. Oxidation samples
were prepared in 1 mL autosampler vials with a total volume of
100 mL. The solutions were added in the following specific order to
prevent premature oxidation of the substrate: antioxidant (0.04–
0.08 M), PFB-13-HOTrE (0.1 M), MeO-AMVN (2.5 mM), and
diluted to 100 mL with benzene. The sealed vials were oxidized
at 37 ◦C for 1 h. After 1 h, the reaction was stopped and
the hydroperoxides were reduced by the addition of 50 mL of
0.1 M butylated hydroxytoluene (BHT) and P(OMe)3 in hexanes.
The samples were then prepared for LC-APCI-MS analysis. The
reaction mixtures were loaded onto Varian Bond Elut, Jr. SPE
cartridges that contained 500 mg of silica that had been pre-
conditioned with 3 mL hexanes. After loading the cartridges, the
samples were washed with 5 mL of a hexanes : EtOAc mixture
(85 : 15) to remove excess antioxidant and unoxidized PFB-13-
HOTrE. The diols were eluted from the cartridge with 2 mL
EtOAc. The solvent was removed under a stream of N2. The
diols were redissolved in 250 mL MeOH : H2O (80 : 20) for LC-MS
analysis. For LC-APCI-MS, the diols were separated using RP-
HPLC using a Supelco Discovery C-18 column (4.6 mm ¥ 25 cm)
and a MeOH : H2O solvent gradient (70 : 30→90 : 10) between
5–45 min at 1 mL min-1. The mass spectrometer was operated
with an APCI source in negative ion mode. The instrumental
conditions were as follows: 5 mA corona discharge, 300 ◦C capillary
temperature, 475 ◦C vaporizer temperature, capillary voltage
-20 V, and tube lens voltage -35 V. The diols were then analyzed
using selective ion monitoring (SIM) of masses 309 and 291 m/z.
The peak area ratio of the 8,13-c,c,t diols were then compared to
the rest of the oxidation products after adjusting the peak areas by
their respective response factors. The response factors convert the
individual areas of the mass spectrometry peaks to match those of
HPLC peak areas from controlled oxidations using a-TOH as the
H-atom donor. A calibration curve from the a-TOH oxidations is
6-ol (23b).
A mixture of 22 (230 mg, 1.26 mmol), p-
toluenesulfonic acid monohydrate (48 mg, 0.25 mmol) and 2,2-
dimethoxypropane (4.63 mL, 37.8 mmol) in dry DMSO (4.6 mL)
was stirred at room temperature overnight. The reaction mixture
was poured to sat. NaHCO3 solution and organic layer was
extracted with EtOAc (3 ¥ 15 mL). The combined organic layer
was washed with water and brine, dried over anhydrous MgSO4
and concentrated. The residue was purified on a Et3N treated silica
gel column (hexanes : EtOAc = 3 : 2) to give 23b (135 mg, 58%) as
1
a caramel. H NMR (300 MHz, DMSO-d6) d 7.70 (s, 1H), 4.63
(s, 2H), 2.88 (s, 3H), 2.25 (s, 3H), 1.95 (s, 3H), 1.34 (s, 6H); 13C
NMR (75 MHz, DMSO-d6) d 146.8, 141.6, 141.2, 131.2, 112.0,
85.7, 59.7, 29.7, 23.8, 19.9, 11.1; IR (KBr) n 3381, 2985, 2931,
1671, 1602, 1452, 1384, 1367, 1242, 1205, 1027, 1004, 804 cm-1;
MS (ESI+): m/z 223.1 [M+H]+; HRMS: calcd for C12H18N2O2
[M+H]+ 223.1441, found 223.1440.
2-Butyl-1,2,5,7-tetramethyl-2,4-dihydro-1H-pyrido[2,3-d][1,3]-
oxazin-6-ol (23c). A mixture of 22 (436 mg, 2.39 mmol),
camphorsulfonic acid (167 mg, 0.72 mmol) and 2-hexanone
(8.84 mL, 71.7 mmol) in dry DMSO (3.5 mL) was stirred at room
temperature overnight. The reaction mixture was poured to sat.
NaHCO3 solution and organic layer was extracted with EtOAc
(3 ¥ 15 mL). The combined organic layer was washed with
water and brine, dried over anhydrous MgSO4 and concentrated.
The residue was purified on a Et3N treated silica gel column
(hexanes : EtOAc = 2 : 1) to give 23c (278 mg, 44%) as a caramel.
1H NMR (300 MHz, DMSO-d6) d 7.64 (s, 1H), 4.60 (s, 2H), 2.85
(s, 3H), 2.23 (s, 3H), 1.94 (s, 3H), 1.61–1.73 (m, 2H), 1.26–1.35 (m,
4H), 1.28 (s, 3H), 0.87 (t, 3H, J = 6.9 Hz); 13C NMR (75 MHz,
CH2Cl2-d2) d 148.7, 142.3, 141.3, 131.7, 113.0, 88.6, 60.6, 37.3,
30.5, 25.8, 23.8, 22.3, 19.4, 14.7, 11.3; IR (KBr) n 3333, 2956,
2928, 2856, 1600, 1460, 1405, 1244, 1220, 1058, 771, 740 cm-1;
MS (ESI+): m/z 265.2 [M+H]+; HRMS: calcd for C15H24N2O2
[M+H]+ 265.1911, found 265.1920.
then utilized to determine kinh
.
5-(Hydroxymethyl)-2,4-dimethyl-6-(methyl(octyl)amino)pyri-
din-3-ol (24). To a solution of 22 (850 mg, 4.64 mmol) in MeOH
(10 mL) were added 1-octanal (1.49 g, 11.6 mmol), acetic acid
(0.88 mL, 15.5 mmol), sodium triacetoxyborohydride (1.08 g,
5.10 mmol). The reaction mixture was stirred for 1 h at room
temperature. Solvent was removed under reduced pressure and
the residue was poured to sat. NaHCO3 solution. The organic
layer was extracted with EtOAc (100 mL ¥ 3), washed with water
Acknowledgements
This work was supported by the National Science Foundation
(USA), and by a Research Foundation Grant funded by the
Korean Government (MOEHRD, Basic Research Promotion
Fund) (KRF-2008-331-E00460).
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8475–8482 | 8481
©

View Article Online
E. Niki, Free Radical Biol. Med., 2010, 48, 1358–1365; (h) J. Lu, O. M.
Khdour, J. S. Armstrong and S. M. Hecht, Bioorg. Med. Chem., 2010,
18, 7628–7638; (i) J. Lu, X. Cai and S. M. Hecht, Org. Lett., 2010, 12,
5189–5191; (j) R. Serwa, T.-g. Nam, L. Valgimigli, S. Culbertson, C. L.
Rector, B.-S. Jeong, D. A. Pratt and N. A. Porter, Chem.–Eur. J., 2010,
16, 14106–14114; (k) T.-g. Nam, J.-M. Ku, H.-g. Park, N. A. Porter and
B.-S. Jeong, Org. Biomol. Chem., 2011, 9, 1749–1755.
3 (a) G. W. Burton, T. Doba, E. J. Gabe, L. Hughes, F. L. Lee, L. Prasad
and K. U. Ingold, J. Am. Chem. Soc., 1985, 107, 7053–7065; (b) G. W.
Burton and K. U. Ingold, Acc. Chem. Res., 1986, 19, 194–201; (c) J.
S. Wright, D. A. Pratt, G. A. DiLabio, T. P. Bender and K. U. Ingold,
Cancer Detect. Prev., 1998, 22, 204; (d) M. C. Foti, E. R. Johnson, M. R.
Vinqvist, J. S. Wright, L. R. C. Barclay and K. U. Ingold, J. Org. Chem.,
2002, 67, 5190–5196.
4 H. J. Kayden and M. G. Traber, J. Lipid Res., 1993, 34, 343–358.
5 G. W. Burton and K. U. Ingold, J. Am. Chem. Soc., 1981, 103, 6472–6477.
6 C. L. Rector, D. F. Stec, A. R. Brash and N. A. Porter, Chem. Res.
Toxicol., 2007, 20, 1582–1593.
7 B. Roscheck Jr., K. A. Tallman, C. L. Rector, J. G. Gillmore, D. A. Pratt,
C. Punta and N. A. Porter, J. Org. Chem., 2006, 71, 3527–3532.
Notes and references
1 (a) L. Valgimigli, G. Brigati, G. F. Pedulli, G. A. DiLabio, M.
Mastragostino, C. Arbizzani and D. A. Pratt, Chem.–Eur. J., 2003, 9,
4997–5010; (b) M. Wijtmans, D. A. Pratt, L. Valgimigli, G. A. DiLabio,
G. F. Pedulli and N. A. Porter, Angew. Chem., Int. Ed., 2003, 42, 4370–
4373.
2 (a) M. Wijtmans, D. A. Pratt, J. Brinkhorst, R. Serwa, L. Valgimigli, G.
F. Pedulli and N. A. Porter, J. Org. Chem., 2004, 69, 9215–9223; (b) T.-
g. Nam, M. Wijtmans, D. A. Pratt and N. A. Porter, Synthesis, 2005,
1397–1404; (c) H.-Y. Kim, D. A. Pratt, J. R. Seal, M. Wijtmans and N.
A. Porter, J. Med. Chem., 2005, 48, 6787–6789; (d) T.-g. Nam, C. L.
Rector, H.-Y. Kim, A. F.-P. Sonnen, R. Meyer, W. M. Nau, J. Atkinson,
J. Rintoul, D. A. Pratt and N. A. Porter, J. Am. Chem. Soc., 2007, 129,
10211–10219; (e) S. Kumar, H. Johansson, T. Kanda, L. Engman, T.
Mu¨ller, M. Jonsson, G. F. Pedulli, S. Petrucci and L. Valgimigli, Org.
Lett., 2008, 10, 4895–4898; (f) S. Kumar, H. Johansson, T. Kanda, L.
Engman, T. Mu¨ller, H. Bergenudd, M. Jonsson, G. F. Pedulli, R. Amorati
and L. Valgimigli, J. Org. Chem., 2010, 75, 716–725; (g) Y. Omata, Y.
Saito, Y. Yoshida, B.-S. Jeong, R. Serwa, T.-g. Nam, N. A. Porter and
8482 | Org. Biomol. Chem., 2011, 9, 8475–8482
This journal is
The Royal Society of Chemistry 2011
©