Scope and limitations of supramolecular autoregulation

Article abstract of DOI:10.1246/bcsj.20150407

Recently, our group has reported on the ureidopyrimidinone (UPy) induced buffering of 2,7-diamido-1,8-naphthyridine (NaPy) and used this phenomenon to regulate the catalysis of the Michael addition of 2,4-pentanedione to trans-a-nitrostyrene. We now show that the observed catalytic activity of NaPy is the result of a strong synergy between NaPy and trace amounts of K2CO3, resulting in a more than 100-fold increase in reaction rate compared to the two compounds separately. By keeping the concentration of K2CO3, as well as NaPy, constant, an improved regulation of the catalytic activity is achieved. We show that the catalytic activity can be precisely regulated in a noncovalent manner via the addition of the UPy motif. Finally, different salts and Michael substrates are screened to assess the selectivity of this catalytic couple and to provide a platform for future research in molecular buffering, regulation, and chemical networks.

Full text of DOI:10.1246/bcsj.20150407

BCSJ Award Article
Scope and Limitations of Supramolecular Autoregulation
Abraham J. P. Teunissen, Roy J. C. van der Haas, Jef A. J. M. Vekemans,
Anja R. A. Palmans, and E. W. Meijer*
Laboratory of Macromolecular and Organic Chemistry, Institute of Complex Molecular Systems Eindhoven University of
Technology, P. O. Box 513, 5600 MB, Eindhoven, The Netherlands
E-mail: e.w.meijer@tue.nl
Received: November 24, 2015; Accepted: December 14, 2015; Web Released: March 15, 2016
E. W. Meijer
E.W. “Bert” Meijer is Distinguished University Professor and Professor of Organic Chemistry at the
Eindhoven University of Technology. After receiving his Ph.D. degree at the University of Groningen in 1982,
he worked for 10 years in industry (Philips and DSM). In 1991 he was appointed in Eindhoven, while he has
part-time positions in Nijmegen and Santa Barbara, CA. Bert Meijer has received a number of awards,
including the International Award of the Society of Polymer Science Japan in 2011, the Cope Scholar Award
of the ACS in 2012, and the Prelog medal in 2014. He is a member of a number of academies and societies,
including the Royal Netherlands Academy of Arts and Sciences, where he is appointed to Academy
Professor in 2014.
Abstract
for example to control cerebral1 and renal2 blood flow, as well
as on a molecular level in the control of gene expression via the
use of riboswitches.3,4 A very simple chemical analogue of
autoregulation is a pH-buffer, in which the influence of acid on
the proton concentration is minimized by the presence of a
conjugated base, resulting in a relatively constant pH. A syn-
thetic system capable of buffering functional molecules, instead
of protons, will provide the opportunity to develop more stable
and life-like chemical networks.
Recently, our group has presented the concept of supra-
molecular buffering, based on the equilibria between a ditopic
supramolecular moiety that can homo-dimerize, and a chain
stopper that is unable to dimerize, but can associate with the
other supramolecular moiety (Figure 1).5,6 Ditopic supra-
molecular compounds have the ability to form either rings
(Kintra) or linear polymers (Kinter), where the stability of the
Recently, our group has reported on the ureidopyrimidinone
(UPy) induced buffering of 2,7-diamido-1,8-naphthyridine
(NaPy) and used this phenomenon to regulate the catalysis of
the Michael addition of 2,4-pentanedione to trans-β-nitro-
styrene. We now show that the observed catalytic activity of
NaPy is the result of a strong synergy between NaPy and trace
amounts of K2CO3, resulting in a more than 100-fold increase
in reaction rate compared to the two compounds separately. By
keeping the concentration of K2CO3, as well as NaPy, constant,
an improved regulation of the catalytic activity is achieved. We
show that the catalytic activity can be precisely regulated in a
noncovalent manner via the addition of the UPy motif. Finally,
different salts and Michael substrates are screened to assess the
selectivity of this catalytic couple and to provide a platform for
future research in molecular buffering, regulation, and chemical
networks.
rings can be defined by the effective molarity (EM = Kintra
K
/
inter).7,8 Since the EM represents a local concentration, the for-
mation of intramolecular contacts, i.e. rings, is more favorable
at low concentrations, while polymerization is favored at high
concentrations. The exact value of the EM depends largely on
the flexibility and length of the spacer connecting the binding
motifs and their relation is relatively well understood.7,8 When
a chain stopper is added to a ditopic compound an equilibrium
is established between cycles with free chain stopper and end-
capped linear polymers. Since at high concentrations polymer-
ization is more favorable, the system will in such cases consist
Introduction
In order for biological systems to remain functional, it is
often vital that a stable working environment is maintained. To
achieve this, regulatory systems have evolved to minimize the
effects of varying inputs on the functional activity of the sys-
tem. Such an adjustment to change is often termed autoregu-
lation. This phenomenon is found both on a macroscopic level,
308 | Bull. Chem. Soc. Jpn. 2016, 89, 308–314 | doi:10.1246/bcsj.20150407
© 2016 The Chemical Society of Japan

of end-capped polymers and a relatively low fraction of free
chain stopper. When the system gets diluted the formation of
rings becomes more favorable, resulting in an increase in the
fraction of free chain stopper compared to the fraction bound to
the polymer. It has been shown that, under certain conditions,
such a dilution-induced release of chain stopper results in
buffering of the chain stopper i.e., the total concentration of the
system can be altered while the concentration of free chain
stopper remains nearly constant (Figure 1).
It has been shown that buffering of 2,7-diamido-1,8-
naphthyridine (NaPy 1) chain stoppers can be achieved in
practice using the ring-chain equilibrium of a ditopic ureido-
pyrimidinone (UPy 2).6 In this case, the concentration of
unbound 1 is buffered over a broad concentration range (c =
10-80 mM). Additionally, it has been found that free NaPy 1
is able to catalyze the Michael addition of 2,4-pentanedione
to trans-β-nitrostyrene (Figure 2).6,9 Moreover, the addition of
UPy 2 to NaPy decreases the rate of the Michael addition. This
has been ascribed to the formation of UPy-NaPy heterodimers,
thereby lowering the free NaPy concentration.10,11 As a result
of the buffering described above, the turnover frequency (TOF)
of the Michael addition in the presence of NaPy 1 and UPy 2
displays a nearly constant value over a wide concentration
range. This buffering phenomenon results in a system with
characteristics similar to autoregulated natural systems, there-
fore this principle has been termed supramolecular autoregu-
lation.6
In our search to optimize the autoregulation and to under-
stand the catalytic functions, we have now discovered that the
catalytic activity of NaPy is in fact the result of a strong
synergy between NaPy and K2CO3.9 Here, we show that this
finding results in an improvement of the autoregulatory prin-
ciple reported originally. The buffering of the TOF can be
optimized provided that the concentration of both NaPy and
K2CO3 are controlled. We complement these findings with an
experimental study on the scope and limitations of the catalytic
couple. To gain more insight into the observed TOF, the influ-
ence of UPy on the reaction rate is examined in more detail.
Finally, various salts and substrate combinations are screened
to illustrate the scope of this catalytic system and broaden the
applicability of the supramolecular autoregulatory concept.
Results and Discussion
Continued research on the UPy-NaPy based autoregulatory
system described above required the synthesis of an additional
batch of NaPy (See Figures S1-S3 for details). Traditionally,
NaPy was purified by recrystallization in ethanol and toluene.12
For practical reasons, we decided to purify NaPy using column
chromatography, leading to a batch of NaPy that surprisingly
was catalytically inactive in the Michael addition of 2,4-
pentanedione to trans-β-nitrostyrene. Since K2CO3 is known to
catalyze certain Michael additions13,14 and was previously used
in the final step in the synthesis of NaPy, we hypothesized that
the work-up procedure via recrystallization might have resulted
Figure 1. The equilibria between a ditopic supramolecular
compound that is able to homo-dimerize and a chain
stopper that is unable to dimerize. The graph depicts the
concentration of free end-capper as a function of the total
concentration, the image was adapted from Ref. 5.
O
O
O
O
NH
O
C11H23
N
N
N
N
C11H23
O
N
N
N
H
H
H
H
(UPy) 3
(NaPy) 1
O
N
HN
NH
O
H
H
O
N
N
O
O
N
N
N
N
N
O
3
10
H
H
H
H
3
O
O
(UPy) 2
O
O
NaPy
NO2
O
O
NO2
+
CDCl3
Figure 2. Chemical structures of NaPy and UPys, and the reported NaPy catalyzed Michael addition of 2,4-pentanedione to trans-β-
nitrostyrene.
Bull. Chem. Soc. Jpn. 2016, 89, 308–314 | doi:10.1246/bcsj.20150407
© 2016 The Chemical Society of Japan | 309

Figure 3. The conversion of the Michael acceptor in the
Michael addition between 2,4-pentanedione (c = 500 mM)
and trans-β-nitrostyrene (c = 100 mM) upon the addition
of combinations of NaPy (c = 20 mM), K2CO3 (c = 5
mM), and UPy (c = 20 mM). The conversion was mea-
sured by 1H NMR using the relative ratio of Michael
acceptor and product. The reaction time is 2 h, the solvent
is CDCl3. All components were combined directly.
in incomplete removal of K2CO3, thereby affecting the catalytic
results. To compare the reaction rates of the Michael addition
of 2,4-pentanedione to trans-β-nitrostyrene in the presence of
either NaPy, K2CO3 or a mixture thereof, several reactions were
performed (Figure 3). Since the dimerization of NaPy and
UPy is typically studied in chloroform,6,12,15 all studies were
performed in CDCl3 at room temperature.
Figure 4. (A) Michael adduct formation for a system
containing 2,4-pentanedione (c = 500 mM), trans-β-nitro-
styrene (c = 100 mM), K2CO3 (c = 1 mM), and different
amounts of NaPy, lines are to guide the eye. (B) The same
experiment as depicted in A, but with 0.5 equivalents of
ditopic UPy 2 (with respect to NaPy) present to buffer the
free NaPy concentration (See ESI Figure S5).
Upon addition of either NaPy or K2CO3 (ground before
use) to 2,4-pentanedione and trans-β-nitrostyrene only trace
amounts of Michael adduct were formed, while the combined
presence of NaPy and K2CO3 gave a quantitative conversion
after ca. 60 min, as revealed by additional measurements. The
addition of 1 equivalent of UPy 2, which complexed to most of
the free NaPy, resulted in a dramatic decrease of the conver-
sion. These results show that there is only significant catalytic
activity when both K2CO3 and free Napy are present. Hence,
it is likely that the previously used NaPy contained traces of
K2CO3.6 The necessity of using both NaPy and K2CO3 to
obtain efficient catalysis is most likely the result of NaPy acting
as a kind of phase-transfer catalyst for K2CO3, thereby forming
an active NaPy¢K2CO3 complex. This can either be via a
“crown-ether like” mechanism, where NaPy complexes K2CO3
as a whole and thereby facilitates its transfer into the liquid
phase; or by NaPy reacting with K2CO3, resulting in KHCO3
increased less strongly with the total concentration of NaPy
in the presence of ditopic UPy 3 than when no UPy was
added (See Figures S17 and S18 in Ref. 6 for more details).
According to our new results, the amount of NaPy¢K2CO3
influenced the rate of the Michael addition. Thus, it should be
possible to construct a system with constant reaction rates at
different concentrations of NaPy-UPy as long as the concen-
tration of K2CO3 is kept constant. To test this, we repeated the
original measurements in the presence of a constant concen-
tration of K2CO3 and different amounts of NaPy without and
with ditopic UPy 3 present. Solutions containing K2CO3 (c = 1
mM), 2,4-pentanedione (c = 500 mM), trans-β-nitrostyrene
(c = 100 mM), NaPy (c = 1-50 mM), and ditopic UPy 2 (0.5
equiv with respect to NaPy) were prepared in CDCl3 (see ESI
Figures S4 and S5 for details). The formation of Michael
¹
and soluble K+NaPy which acts as the active base for the
reaction.16 Hence, the nature of the ground K2CO3 can be of
influence in this heterogeneous process to make the active
catalyst. The presence of such a complex also explains why the
recrystallization step to purify NaPy has been ineffective in
removing all K2CO3.
1
adduct was monitored over time by H NMR (Figure 4).
Figure 4A shows that the reaction rate of the Michael
addition in non-buffered conditions (i.e., no UPy 3 present)
increases with roughly a factor 2 when the concentration of
NaPy is increased from 1 to 5 mM. A further increase of the
NaPy concentration does not lead to a significant increase in the
reaction rates; the conversion profiles for 10 and 40 mM NaPy
are similar to those observed for 5 mM NaPy concentration.
In the original autoregulation article,6 the equilibria between
ditopic UPy 2 and NaPy 1 afforded a system in which the con-
centration of free NaPy (i.e., the active catalyst in combination
with K2CO3), remained constant over a broad concentration
range. As a result, the reaction rates of the Michael addition
310 | Bull. Chem. Soc. Jpn. 2016, 89, 308–314 | doi:10.1246/bcsj.20150407
© 2016 The Chemical Society of Japan

This is the result of the much smaller and constant amount of
K2CO3 (c = 1 mM) becoming rate limiting. In other words, the
addition of more NaPy will no longer increase the NaPy¢K2CO3
concentration and hence the reaction rate is not enhanced.
In contrast, if the reaction is carried out under the same
conditions but with 0.5 equivalent of ditopic UPy 2 present
(Figure 4B), the free NaPy concentration is buffered at
approximately 1 mM. This buffering of the concentration of
active phase-transfer catalyst results in conversion profiles that
are independent of the total NaPy-UPy concentration. This
indicates that the reaction rates are similar and have become
independent of the total NaPy concentration. While in our
studies the concentration of K2CO3 is kept at a constant level,
it has been unintentionally increased simultaneously with the
total NaPy concentration in the experiments reported previ-
ously.6 This has no significant effect on the UPy-NaPy
equilibria since the concentration at which free NaPy is
buffered (µ1 mM) is very similar in both cases. However, the
reaction rates observed are much more constant in this study
compared to the experiments reported previously (See Ref. 6,
Figure S18). This is the consequence of keeping both the
K2CO3 and NaPy concentration constant, instead of only the
latter. Thus, we hereby confirmed that the previously reported
supramolecular autoregulation as a result of a buffered free
NaPy concentration is indeed possible and becomes even better
when the concentration of K2CO3 is kept constant.
Although there are many, potentially more efficient, catalysts
for the Michael addition, our NaPy-K2CO3 system has the
unique possibility of exploiting the UPy-NaPy dimerization
to regulate the free NaPy concentration. This provides a handle
to control catalytic activity in a noncovalent and reversible
manner, thereby creating a direct link between noncovalent and
covalent chemistry. In light of future applications, we set out to
study the scope and limitations of the NaPy-K2CO3 catalytic
couple. In order to determine the influence of the amount of
UPy on the reaction rate in more detail, the coupling of 2,4-
pentanedione (c = 40 mM) to trans-β-nitrostyrene (c = 40 mM)
was performed in the presence of NaPy (c = 5 mM), K2CO3
(c = 5 mM), and various amounts of monotopic UPy 3. At all
UPy concentrations, >99% of UPy was present as UPy-NaPy
heterodimer. When all components were combined directly,
an initial lag-phase of approximately 40 min was observed,
which we attributed to the time required to form a catalytically
active NaPy¢K2CO3 complex (Figures S6 and S7 for details).
As expected, when NaPy 1, UPy 3, and K2CO3 were stirred
overnight before adding the Michael substrates, the lag-phase
is not observed. Our results show that there is an exponential
decay in the reaction rate upon increasing the amount of UPy
(Figure 5). This nonlinearity shows that the reaction order of
NaPy is larger than unity, which suggests that more than one
NaPy is present in the catalytically active species.
Figure 5. The initial reaction rates of the Michael addition
versus the equivalents of UPy 3 in relation to NaPy 1.
Solutions of NaPy 1 (5 mM), K2CO3 (5 mM), and different
amounts of UPy 3 in CDCl3 were allowed to stir for 24 h
before 2,4-pentanedione (40 mM) and trans-β-nitrostyrene
(40 mM) were added. The measurements were started
directly after the addition of the Michael substrates. See
ESI (Figures S6 and S7) for additional experimental details
and results.
ing rate limiting. Additionally, high K2CO3 concentrations
result in the formation of a poorly soluble yellow powder and
the disappearance of part of the trans-β-nitrostyrene from the
solution; as evidenced by NMR spectroscopy. Most likely, this
precipitate is the result of complexation between K+ and the
nitro-moiety,18 which is corroborated by the fact that this
precipitate dissolves again when 18-crown-6 is added. The
catalytic activity of NaPy in the presence of other salts such as
CaCO3, Na2CO3, and KCl is low (Figure 6B), with the excep-
tion of Cs2CO3 (see ESI Figure S10 for 1H NMR data). In
addition, the reaction still occurs when NaPy is replaced by
catalyst 18-crown-6, albeit less efficiently.
Finally, the scope of substrate pairs suitable for the
autoregulatory system were investigated; we selected sixteen
Michael donors and acceptors in the screening for their ability to
form Michael adducts in the presence of NaPy and K2CO3 (See
ESI Table S1 and Figures S11-S14). Interestingly, only four
combinations showed any conversion after the addition of NaPy
and K2CO3 (Figure 7). Of these, the synergy between NaPy and
K2CO3 is only observed for the coupling of 2,4-pentanedione
to either trans-β-nitrostyrene or 1-(tert-butyl)-1H-pyrrole-2,5-
dione, highlighting the high sensitivity of the catalytic system
towards the substrates used. While the reaction with 1-(tert-
butyl)-1H-pyrrole-2,5-dione was slower, it repeatedly afforded
the product in quantitative yields. In contrast to the coupling of
2,4-pentanedione to trans-β-nitrostyrene, which gave some
precipitates at high K2CO3 concentrations (vide supra).
Next the influence of the base and substrate combination on
the catalytic activity was investigated. The concentration of
K2CO3 was varied and other salts were tested, as well as the
replacement of NaPy by 18-crown-6, a known phase-transfer
catalyst for K2CO3.17 Increasing the amount of K2CO3 relative
to NaPy resulted in a roughly linear increase in conversion,
with slightly lower values at higher K2CO3 concentrations
(Figures 6A, S8, and S9). This is attributed to K2CO3 becom-
Conclusion
Here, we have shown that there is a high degree of synergy
between NaPy and K2CO3 towards the catalysis of selected
Michael additions in CDCl3. The synergy is proposed to be the
result of NaPy acting as a kind of phase-transfer catalyst for
K2CO3 to generate an active catalytic base. We demonstrate
that the observed buffering of the TOF of the NaPy-catalyzed
Bull. Chem. Soc. Jpn. 2016, 89, 308–314 | doi:10.1246/bcsj.20150407
© 2016 The Chemical Society of Japan | 311

Experimental
General.
Unless noted otherwise all chemicals were
purchased from Sigma Aldrich, K2CO3 was ground before use.
Michael additions were performed on 1-2 mL scale in 45 © 27
mm vials using CDCl3 from Cambridge Isotope Laboratories.
NMR spectra were taken on a 400 or 500 MHz (1H) Varian
Spectrometer and results were processed using VNMRJ 3.2a
software. All reactions in the synthesis of NaPy and UPy
were performed under argon. Unless otherwise noted, the
Michael substrates were combined directly with the NaPy and
K2CO3.
Measuring the Initial Reaction Rates of the Michael
Addition in the Presence of Various Amounts of UPy. In
a typical experiment NaPy 1 (5 mM), K2CO3 (5 mM), and
various amounts of UPy 3 were dissolved in 15 mL of CDCl3.
The mixture was stirred for 24 h to allow for the catalytically
active complex to form. Subsequently trans-β-nitrostyrene (40
mM) and 2,4-pentanedione (40 mM) were added. Samples of
0.5 mL were taken in roughly 5 min intervals and analyzed
1
directly using H NMR. To prevent concentration of K2CO3,
the samples were returned to the reaction mixture directly after
analysis (µ2-3 min later). Conversions were determined using
the standard procedure described in the materials and method
section. The exact amount of UPy was determined by 1H NMR.
In the “direct start” measurement, only NaPy 1 was stirred
overnight in CDCl3, after which K2CO3 and the Michael sub-
strates were added and the measurement started. The measure-
ment was performed on the same scale and concentration as
described above.
Repeating the Supramolecular Autoregulation Experi-
ments with Constant K2CO3 Concentration. The measure-
ments without UPy where carried out by preparing a 5 mL
solution of NaPy and K2CO3 (c = 1 mM) which was stirred
overnight. A 5 mL solution of 1 M 2,4-pentanedione and 0.2 M
trans-β-nitrostyrene was then added after which the solution
was stirred and 0.5 mL NMR samples were taken at regular
intervals. To minimize concentrating the solid K2CO3 over
time, the samples were poured back into the reaction mixture
immediately after measurement. The measurements with UPy
were carried out using the ditopic UPy 2. Ditopic UPy was
synthesized according to a literature procedure.6 The reactions
were carried out in an identical manner as for the measurements
without UPy, with the only difference that they were performed
at 20 mL scale to minimize weighing errors between the NaPy
and UPy.
Synthesis of 2,7-Diamido-1,8-naphthyridine (NaPy 1). 7-
Amino-1,8-naphthyridin-2-ol (4): Malic acid (9.6 g, 70.4
mmol) and pyridine-2,6-diamine (7.0 g, 64.0 mmol) were
grinded to a fine powder and cooled in an ice bath. Sub-
sequently, concentrated sulfuric acid (32 mL) was dropwise
added. The solution was heated under Ar to 110 °C for 3 h,
poured over ice and made alkaline with concentrated ammoni-
um hydroxide until a pH of 8 was reached. Subsequently, the
precipitate was filtrated and washed with H2O. Removal of
the solvent in vacuo yielded the product (11.9 g, quantitative).
1H NMR (400 MHz, DMSO-d6): ¤ 10.60 (bs, 1H, OH), 7.61 (d,
2H, J = 9.0 Hz, Ar), 6.80 (s, 2H, NH2), 6.33 (d, 1H, J = 8.5
Hz, Ar), 6.10 (d, 1H, J = 9.2 Hz, Ar). 13C NMR (100 MHz,
Figure 6. (A) The conversion of the Michael addition
between 2,4-pentanedione (c = 100 mM) and trans-β-
nitrostyrene (c = 100 mM) in the presence of NaPy (c =
10 mM) and different amounts of K2CO3. The conversion
was measured by 1H NMR using the relative ratio of
Michael acceptor and product. The measurements were
performed in duplo, error bars depict the standard devia-
tion. Note that we reduced the concentration of 2,4-
pentanedione from the usual 500 mM to 100 mM in order
to slow down the kinetics. (B) The conversion of Michael
adduct formed of 2,4-pentanedione (c = 500 mM) to trans-
β-nitrostyrene (c = 100 mM) in the presence of NaPy or
18-crown-6 (c = 20 mM) and different salts (c = 5 mM),
for KCl c = 10 mM to keep the potassium concentration
equal to that of the K2CO3 measurements.
Michael addition reported previously by our group is the result
of the unintentional presence of K2CO3. Repeating several of
the experiments reported earlier shows that constant reaction
rates can indeed be achieved at different NaPy concentrations,
as long as the K2CO3 concentration is kept constant. Only
unbound NaPy is able to act as a catalyst, allowing the catalytic
activity to be modulated by the addition of the complementary
UPy motif. As a result, we obtain a system that shows supra-
molecular autoregulation behavior. The NaPy-K2CO3 catalytic
couple is highly selective towards the used Michael substrates
and the used salt. Also, only small amounts of K2CO3 suffice to
generate an active system. We believe that this work will con-
tribute to the further development of supramolecular organo-
catalytic systems and the construction of synthetic chemical
networks.
312 | Bull. Chem. Soc. Jpn. 2016, 89, 308–314 | doi:10.1246/bcsj.20150407
© 2016 The Chemical Society of Japan

Figure 7. The conversion of the Michael acceptor in the Michael addition between various substrate combinations in CDCl3 after
2 h; Michael donor (c = 500 mM), Michael acceptor (c = 100 mM), NaPy (c = 20 mM), and/or K2CO3 (c = 5 mM). The conver-
sion was measured by 1H NMR using the relative ratio of Michael acceptor and product. All components were combined directly.
DMSO-d6): ¤ 168.69, 165.58, 155.61, 144.70, 142.34, 120.13,
110.11, 110.09.
solution was slowly poured into vigorously stirred iced water
(2 L), followed by neutralization with concentrated aqueous
NH3 solution to pH 8. The product was obtained as a white
N-(7-Oxo-7,8-dihydro-1,8-naphthyridin-2-yl)dodecan-
amide (5): A mixture of 7-amino-1,8-naphthyridin-2-ol (4)
(14.0 g, 87.0 mmol) and dodecanoyl chloride (34.4 g, 147.9
mmol) in dry pyridine (36 mL) was stirred overnight under Ar
at 110 °C and subsequently allowed to cool to room temper-
ature. The precipitate was filtered off and recrystallized from
toluene. The product was obtained as a brown solid (18.2 g,
61%). 1H NMR (400 MHz, CDCl3): ¤ 12.87 (bs, 1H, NH),
11.84 (bs, 1H, NH), 8.43 (d, 1H, J = 8.7 Hz, Ar), 7.99 (d, 1H,
J = 8.7 Hz, Ar), 7.72 (d, 1H, J = 9.4 Hz, Ar), 6.63 (d, 1H,
J = 9.4 Hz, Ar), 2.67 (t, 2H, J = 7.4 Hz, O=C-CH2), 1.76 (m,
2H, J = 7.6, 7.4 Hz, O=C-CH2-CH2), 1.25 (m, 16H, alkyl-
CH2), 0.87 (t, 3H, alkyl-CH3). 13C NMR (100 MHz, CDCl3):
¤ 174.52, 165.27, 154.29, 148.62, 139.79, 139.05, 119.79,
111.17, 110.75, 37.10, 31.92, 29.66, 29.25, 25.38, 22.69, 14.13.
N-(7-Chloro-7,8-dihydro-1,8-naphthyridin-2-yl)dodecan-
1
powder by filtration of the precipitate (17.2 g, 89%). H NMR
(400 MHz, CDCl3): ¤ 8.58 (d, 1H, J = 8.9 Hz, Ar), 8.32 (bs,
1H, NH), 8.18 (d, 1H, J = 8.9 Hz, Ar), 8.09 (d, 1H, Ar), 7.41
(d, 1H, J = 8.4 Hz, Ar), 2.47 (t, 2H, J = 7.6 Hz, O=C-CH2),
1.76 (m, 2H, J = 7.6, 7.4 Hz, O=C-CH2-CH2), 1.26 (m, 16H,
alkyl-CH2), 0.88 (t, 3H, J = 6.7 Hz, alkyl-CH3). 13C NMR
(100 MHz, CDCl3): ¤ 174.42, 154.12, 139.14, 138.74, 122.05,
115.18, 76.67, 38.07, 31.89, 29.58, 29.42, 29.31, 29.11, 25.21,
22.67, 14.11. MALDI-ToF MS: calculated for C20H30ClN3O
361.91, observed m/z 362.25 [M + H+].
N,N¤-(1,8-Naphthyridine-2,7-diyl)didodecanamide
(1):
A
flask was charged with N-(7-chloro-7,8-dihydro-1,8-
naphthyridin-2yl)dodecanamide (6) (15.6 g, 42.8 mmol),
dodecanamide (10.3 g, 51.3 mmol), Pd(OAc)2 (593 mg, 2.6
mmol), Xantphos (3.3 g, 5.8 mmol), K2CO3 (5.9 g, 42.8 mmol),
and dry dioxane (250 mL). Oven-dried molecular sieves (4 ¡)
were added and the mixture was stirred overnight at room
temperature under Ar. Subsequently, the mixture was heated to
80 °C and stirred overnight under Ar. After cooling to room
amide (6):
A mixture of N-(7-oxo-7,8-dihydro-1,8-
naphthyridin-2-yl)dodecanamide (5) (18.2 g, 50.1 mmol) in
POCl3 (150 mL) was stirred at 95 °C for 4 h under Ar and sub-
sequently allowed to cool to room temperature. The remaining
Bull. Chem. Soc. Jpn. 2016, 89, 308–314 | doi:10.1246/bcsj.20150407
© 2016 The Chemical Society of Japan | 313

temperature, the mixture was filtered and the residue was rinsed
with CHCl3. Recrystallization in ethanol and purification by
flash chromatography (80% CHCl3/20% EtOAc) yielded the
We would like to thank Tim Paffen for useful discussions
and providing bifunctional UPy 3. This work is financed by the
Dutch Organisation for Scientific Research (NWO-TOP grant:
No. 10007851), the Dutch Ministry of Education, Culture and
Science (Gravity program 024.001.035), and the European
Research Council (FP7/2007-2013, ERC Advanced Grant
No. 246829).
1
product as a white solid (16.5 g, 73%). H NMR (400 MHz,
CDCl3): ¤ 8.42 (d, 2H, J = 8.8 Hz, Ar), 8.14 (d, 2H, J =
8.8 Hz, Ar), 8.12 (bs, 2H, NH), 2.47 (t, 4H, J = 7.6 Hz,
O=C-CH2), 1.56 (m, 4H, J = 8.0, 7.6 Hz, O=C-CH2-CH2),
1.26 (m, 32H, alkyl-CH2), 0.88 (t, 6H, alkyl-CH3). 13C NMR
(100 MHz, CDCl3): ¤ 172.2, 153.74, 138.98, 113.34, 110.01,
76.75, 38.13, 31.90, 29.60, 29.44, 29.33, 29.15, 25.29, 22.68,
14.12. MALDI-ToF MS: calculated for C32H52N4O2 524.78,
observed m/z 525.43 [M + H+], 1087.79 [dimer + K+].
Elemental analysis: calculated for C32H52N4O2: C, 73.24; H,
9.99; N, 10.68; O, 6.10%. Found: C, 73.35; H, 9.59; N,
10.26%.
Supporting Information
Characterization data including 1H and 13C NMR spectra and
kinetic experiments of the Michael additions. This material is
available on http://dx.doi.org/10.1246/bcsj.20150407.
References
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314 | Bull. Chem. Soc. Jpn. 2016, 89, 308–314 | doi:10.1246/bcsj.20150407
© 2016 The Chemical Society of Japan