Combinatorial aid for underprivileged scaffolds: Solution and solid-phase strategies for a rapid and efficient access to novel aza-diketopiperazines (aza-DKP)

Article abstract of DOI:10.1021/co300015k

An efficient solution-phase synthesis of aza-diketopiperazines (aza-DKP, triazinediones) is reported. A structurally diverse collection of c-[aza-alkylGly-Pro] derivatives and yet unreported 2,4,5-trisubstituted-1,2,4- triazine-3,6-diones has been synthesized starting from Fmoc-l-Pro-OH and various Fmoc-l-amino acids. To extend the practical value of this class of dipeptidomimetics, a general solid-phase synthesis approach amenable to library production was developed on both Wang-PS and HMBA-PS resins. The final acidic treatment of the resins in TFA/water mixture at room temperature enabled the rapid and quantitative cyclization/release highly pure triazinediones. The conformational preferences and the spatial organization of the three substituents of a representative 2,4,5-trisubstituted-1,2,4-triazine-3,6-dione were investigated by X-ray diffraction and ¹H NMR spectroscopy.

Full text of DOI:10.1021/co300015k

Research Article
pubs.acs.org/acscombsci
Combinatorial Aid for Underprivileged Scaffolds: Solution and
Solid-phase Strategies for a Rapid and Efficient Access To Novel
Aza-diketopiperazines (Aza-DKP)
Dominique Bonnet,*,§ Jean-Francois Margathe,§ Sally Radford,† Elsa Pflimlin,§ Stephanie Riche,§
̧
́ ́
Pete Doman,‡ Marcel Hibert,§ and A. Ganesan*,∥
§Laboratoire d’Innovation Ther
67412 Illkirch, France
‡Maybridge, Trevillet, Tintagel, Cornwall PL34 OHW, U. K.
́ ́ ́
apeutique, UMR7200 CNRS, Universite de Strasbourg, Faculte de Pharmacie, 74 route du Rhin,
†School of Chemistry, University of Southampton, Southampton SO17 1BJ, U. K.
∥School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U. K.
S
* Supporting Information
ABSTRACT: An efficient solution-phase synthesis of aza-
diketopiperazines (aza-DKP, triazinediones) is reported. A
structurally diverse collection of c-[aza-alkylGly-Pro] deriva-
tives and yet unreported 2,4,5-trisubstituted-1,2,4-triazine-3,6-
diones has been synthesized starting from Fmoc-L-Pro-OH
and various Fmoc-L-amino acids. To extend the practical value
of this class of dipeptidomimetics, a general solid-phase synthesis approach amenable to library production was developed on
both Wang-PS and HMBA-PS resins. The final acidic treatment of the resins in TFA/water mixture at room temperature enabled
the rapid and quantitative cyclization/release highly pure triazinediones. The conformational preferences and the spatial
organization of the three substituents of a representative 2,4,5-trisubstituted-1,2,4-triazine-3,6-dione were investigated by X-ray
1
diffraction and H NMR spectroscopy.
KEYWORDS: aza-DKP, triazinedione, heterocycle, peptidomimetic, solid-phase synthesis, molecular diversity
should then exist examples of “underprivileged scaffolds” that
are intrinsically suitable for drug discovery applications but in
practice are underrepresented or absent. For example, scientists
at Celltech have recently generated a list of heterocycles that
have yet to be synthesized and would have the advantage
of novelty compared to the patent literature.12 In the same
way, we believe the attractive features of DKPs as a privileged
scaffold can be carried over to novel DKP-like scaffolds that are
less well-known and provide interesting opportunities for lead
discovery. One such example is the 1,2,4-triazine-3,6-dione
(aza-DKP, Figure 1). This class of heterocycles can be viewed
as constrained cyclic dipeptidomimetic DKP analogues where-
by one Cα-stereogenic center has been replaced by a planar
nitrogen. Compared to the extensive medicinal and combina-
torial chemistry literature on DKPs, there are very few examples
on the synthesis of aza-DKPs. Pinnen et al. described the
pioneering synthesis of c-[aza-Phe-Pro] in their research toward
pseudopeptidic ergopeptines.13 More recently, two groups have
devised synthetic routes to access c-[aza-alkylGly-Pro] deriva-
tives.14,15 A few examples of 1,4-di- and 1,4,5-trisubstituted-
1,2,4-triazine-3,6-diones synthesis have also been described
INTRODUCTION
■
The vast majority of biologically active organic compounds are
heterocyclic in nature, a fact that has been heavily exploited by
the pharmaceutical industry.1,2 Among these compounds, 2,5-
diketopiperazines (DKPs) occupy a special position as they link
peptide and heterocycle chemical space. DKPs result from the
cyclization of a linear dipeptide and are the smallest possible
cyclopeptides. This motif is present in the core of many natural
products and synthetic compounds that display interesting
therapeutic properties.3,4 DKPs have been shown to inhibit
several enzymes including PDE-5 by the clinically approved
drug Cialis, as well as to recognize, modulate, and control the
activity of many receptors, such as calcium channels and opioid,5
GABAergic,6 serotoninergic 5HT1A,7 and oxytocin receptors.8
Thus, the DKPs are an excellent example of a privileged scaffold
that confers biological activity across a variety of drug targets.9−11
From the combinatorial point of view, DKPs have the further
advantage of ease of synthesis from dipeptides that can be
assembled with high diversity from commercially available amino
acids. While the concept of privileged scaffolds is a useful
strategy in drug discovery, it is nevertheless self-fulfilling as it is
based on precedent. A scaffold that leads to biologically active
compounds will attract interest by medicinal chemists who will
then produce more examples of the same and discover new
active compounds that further confirm the hypothesis. There
Received: February 2, 2012
Revised: March 28, 2012
Published: March 29, 2012
© 2012 American Chemical Society
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ACS Combinatorial Science
Research Article
sized N′-alkyl tert-butyl carbazate; and (3) the final depro-
tection and cyclization of the semicarbazide precursor to afford
triazinediones.
N′-Alkyl/Aryl tert-Butyl Carbazates Synthesis. On the basis
of literature,18 commercially available tert-butyl carbazate was
reacted with benzaldehyde in THF for 2 days. Without
isolation, the corresponding hydrazone was subsequently
reduced in the presence of sodium cyanoborohydride
(NaCNBH3), AcOH 1% to provide hydrazine 6a in a moderate
56% yield. In an attempt to improve the yield of the reaction,
hydrazone formation was performed in toluene at 50 °C
overnight. Following isolation by simple precipitation and
purification by recrystallization, hydrazone 5a was reduced as
described above to furnish hydrazine 6a in an improved 85%
yield (Scheme 2).
Figure 1. General structure of diketopiperazines (DKP) and aza-
diketopiperazines (Aza-DKP).
either in solution or on solid-phase.16,17 However, to date, no
examples of 2,4,5-trisubstituted-1,2,4-triazine-3,6-diones have
been reported in the literature.
a
Scheme 2. Synthesis of N′-Alkyl/Aryl tert-Butyl Carbazates
This novel heterocycle is particularly appealing in term of
“drug-likeness” because it fulfills the following requirements:
(1) it is a compact six-membered ring heterocycle of low
molecular weight, which can then be decorated by a set of three
variable substituents; (2) it contains five heteroatoms able to
increase the overall hydrophilicity of compounds; (3) the total
number of H-bond donors and acceptors in the core is one and
five, respectively, meaning that decoration of the core can add
several such groups without infringing Lipinski’s “Rule of Five”.
To exploit the potential of this “underprivileged scaffold”, a
combinatorial route that can generate new examples of the
heterocycle are needed. In this article, we report a concise and
rapid strategy toward c-[aza-alkylGly-Pro] derivatives and 2,4,5-
trisubstituted-1,2,4-triazine-3,6-diones that has been developed
in solution-phase and advantageously adapted to solid support
to afford a set of novel triazinediones. Conformational and
structural features of one representative example were
a
Reagents and conditions: (i) R4CHO, toluene, 50 °C; (ii) (a)
NaBH3CN, THF, p-TsOH, (b) NaOH, MeOH, rt; (iii) Ethyl
bromoacetate, water, 1 h, rt; (iv) LiOH, dioxane/water, 1 h, 40 °C;
(v) propargyl bromide, K2CO3, THF/DMF (9/1), overnight, rt.
With these optimized conditions, a set of structurally diverse
hydrazines 6b−n were thus obtained with yields ranging from
40% to 75% for the two steps (Table 1). However, for com-
pounds 6o, p the reduction of the precursor hydrazones was
found more difficult to achieve. Prolonged heating at 40 °C
overnight failed to provide the expected hydrazines. Therefore,
an alternative protocol was developed on the basis of the use of
p-toluenesulphonic acid (p-TsOH) instead of acetic acid.19
Hydrazones 5o, p were refluxed in THF for four hours in the
presence of NaBH3CN and p-TsOH to successfully provide
hydrazines 6o, p in 73% and 69% yields, respectively, for the
two steps. Hydrazines 7 and 9 (Scheme 2) were prepared
by direct alkylation of tert-butyl carbazate with either ethyl
bromoacetate or propargyl bromide.20,21 The slow addition of
bromo derivatives to an excess of tert-butyl carbazate (3−5
equiv) enabled the formation of dialkylated hydrazine by-
products to be minimized. Propargyl 9 and ester 7 were isolated
by column chromatography in 48% and 76% yield respectively.
A subsequent hydrolysis of ester 7 under basic conditions gave
access to hydrazine 8 in 79% yield. Finally, one example of aryl
hydrazine (compound 10) was also prepared by condensation
of phenylhydrazine to di-tert-butyl dicarbonate (Boc2O) in
refluxing dichlororomethane for 2 h (72% yield).
1
investigated by X-ray diffraction and H NMR spectroscopy.
RESULTS AND DISCUSSION
■
Solution-Phase Synthesis. On the basis of the results
published by Obreza et al.14 a synthetic approach was devised
starting from commercially available α-amino acid esters
(Scheme 1). This approach features mainly three steps: (1)
a
Scheme 1. Solution-Phase Approach Towards aza-DKP
Alkylated Amino Ester Synthesis. Their preparation was
performed as previously described in the literature starting from
α-amino acid esters 1 (Scheme 1).22 Imine formation was
accomplished in the presence of NEt3 either in THF or MeOH.
The addition of MgSO4 was found to facilitate the imine
formation. The subsequent reduction was carried out with
sodium borohydride (NaBH4) in MeOH for 1 h. According to
this one-pot process, six alkylated amino esters 2a−f were
prepared in yields ranging from 65 to 79% (Table 2).
a
Reagents and conditions: (i) (a) aldehyde, NEt3, MeOH, overnight,
rt; (b) NaBH4, MeOH, 30 min, rt; (ii) R3NHNHBoc, BTC, CH2Cl2,
or THF, Hunig’s base, 10 min, rt; (iii) p-TsOH, toluene, reflux, 2.5 h
(method A) or Amberlyst 15 resin, MeOH, μwave 150 W, 120−
140 °C, 15−20 min (method B).
̈
the reductive alkylation of α-amino acid esters with various
aldehydes; (2) the semicarbazide formation with presynthe-
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Semicarbazide Cyclization Studies. This final step was
investigated by using model semicarbazide 3i. Attempts to
perform the cyclization applying Obreza conditions,14 that is,
HCl in acetic acid, failed to afford the expected triazinedione 4i.
Following optimization, the triazinedione was finally obtained
(58% yield) in the presence of p-TsOH in refluxing toluene
for 30 min (Method A). Microwave-assisted heating in the
presence of Amberlyst 15 resin, MeOH at 140 °C for 20 min
(Method B) gave similar results (55% yield). Nevertheless, the
use of polymer-supported p-TSOH (Amberlyst 15 resin)
made the final workup easier. Structure assignment for 4i was
Table 1. Representative N′-Alkyl tert-Butyl Carbazate
Derivatives
1
done by H, 13C NMR and IR analysis and compared to the
data previously described in the literature.9 The optimized
synthetic protocol was then employed with semicarbazides
3a−w above to access both novel c-[Aza-alkylGly-Pro] deri-
vatives and 2,4,5-trisubstituted-1,2,4-triazine-3,6-diones
(Table 4). In all cases but five (compounds 4k, l, p, t), the
expected triazinediones were isolated in low to moderate
yields. Extending the time or increasing the temperature did
not improve yields but led in most cases to the decomposition
of semicarbazides. For triazinediones 4s and 4u, the best
conversion was obtained by replacing MeOH by acetonitrile.
Noteworthy, when R3 = aryl (semicarbazide 3c), the cycliza-
tion did not proceed and only deprotected semicarbazide
was recovered. Semicarbazides 3k, l, p, t, decomposed under
the reaction conditions without forming any corresponding
triazinediones.
a
b
Overall yields from tert-butyl carbazate. p-TSOH was used instead of
c
d
AcOH. Two steps overall yields. Boc2O, CH2Cl2, phenylhydrazine,
2.5 h.
The solution-phase approach developed in the first part of
this study allowed for the access to novel and structurally
diverse collections of aza-DKP heterocycles. Given the pro-
mising results obtained above, we decided to undertake a solid-
phase approach with the aim: (1) to facilitate the access
to such compounds by avoiding intermediate purification;
(2) to improve both the yield and purity of final compounds;
(3) to develop a strategy amenable to libraries production in
a multiparallel format.
Solid-Phase Approach. Synthesis on Wang-PS Resin.
The optimization of the process was performed on the model
2,4,5-tribenzyl-1,2,4-triazine-3,6-dione 16a starting from the
commercially available Fmoc-L-phenylalanine-Wang-PS resin
11 (Scheme 3). All solid-phase reactions were monitored by
using different colorimetric tests (chloranil, trinitrobenzene
sulfonate (TNBS), Ninhydrin)23 but also by treatment of an
aliquot of resin in trifluoroacetic acid (TFA)/water (95:5)
mixture followed by liquid chromatography−mass spectrome-
try (LC-MS) analysis of the crude sample.
Our approach to the solid-phase synthesis of model
triazinedione 16a involved a reductive amination step of the
resin-bound primary amine 12 with benzaldehyde in
trimethylorthoformate (TMOF), followed by the reduction of
the imine with NaBH3CN in the presence of 1% AcOH.24,25 To
avoid bis-alkylation, the excess of benzaldehyde was removed
by filtration prior to the imine reduction, leading to the clean
secondary amine 13. Next, the preparation of solid-supported
semicarbazide 15 was attempted following procedures described
in the literature for the solid-phase synthesis of azapeptides, that
is, the solution-phase activation of carbazate 6a with phosgene
prior to the addition to the resin-bound secondary amine
13.26 However, in our hand, this approach failed to provide the
expected semicarbazide, only the starting secondary amine being
detected by LC-MS. This result suggests that the steric hindrance
of the resin-bound secondary amine 13 prevents the reaction
with the activated carbazate. Hence, the semicarbazide formation
Table 2. Alkylated Amino Esters 2a−f
a
compound
R1
R2
yield (%)
2a
2b
2c
2d
2e
2f
(CH3)2CHCH2-
HOCH2-
Bn-
Bn-
Bn-
Bn-
67
95
65
74
79
72
2-indoleCH2-
Bn-
(CH3)2CHCH2-
(CH3)2CHCH2-
4-NO2Bn-
4-MeOBn-
a
Overall yields from L-amino esters 1.
Semicarbazide Formation. Starting from alkylated amino
esters 2a−f, optimized conditions for the synthesis of the
semicarbazide derivatives were investigated by the fine-tuning
of various parameters such as: the nature of the carbonyl activa-
tion reagents (bis(trichloromethyl)carbonate (BTC), phosgene,
carbonyldiimidazole), the nature of the solvent (CH2Cl2 vs
THF), the sequence of addition of the reagents and the reaction
time. Best results were obtained by activating N′-alkyl/aryl tert-
butyl carbazates with BTC in the presence of Hunig’s base before
̈
adding dropwise the resulting mixture to the alkylated amino
esters. The nature of the solvent used to carry out this latter
reaction was found to have a profound effect on the yield. Table
3 describes semicarbazides synthesized following the optimal
experimental conditions. For compounds 3a, c, h, the reaction
performed in CH2Cl2 failed to provide the expected semi-
carbazides whereas in THF the yields were 81%, 48% and 55%
respectively. These results could be ascribed to the general
better solubility of N′-alkyl/aryl tert-butyl carbazates and alkylated
amino esters in THF.
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Table 3. Semicarbazides 3a−w
a
yield (%)
compound
R1
R2
R3
CH2Cl2
THF
81
3a
3b
3c
3d
3e
3f
HOCH2-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Ph-
0
66
0
(CH3)2CHCH2-
(CH3)2CHCH2-
(CH3)2CHCH2-
(CH3)2CHCH2-
Bn-
48
4-MeOBn-
4-MeOBn-
4-NO2Bn-
90
4-NO2Bn-
Bn-
76
82
88
55
3g
3h
3i
Bn-
Bn-
CH3(CH2)4-
3,4,5-(MeO)3Bn-
Bn-
2-indoleCH2-
-(CH2)3-
Bn-
0
3j
-(CH2)3-
3,4,5-(MeO)3Bn-
2-furanCH2-
2-thiopheneCH2-
2-MeOBn-
3-MeOBn-
3,5-(MeO)2Bn-
2,4,6-(MeO)3Bn-
2-BrBn-
3k
3l
-(CH2)3-
62
73
68
64
86
56
98
90
52
98
94
92
93
-(CH2)3-
3m
3n
3o
3p
3q
3r
-(CH2)3-
-(CH2)3-
-(CH2)3-
-(CH2)3-
-(CH2)3-
-(CH2)3-
3-BrBn-
3s
3t
-(CH2)3-
4-BrBn-
-(CH2)3-
4-MeOBn-
4-NO2Bn-
3u
3v
3w
-(CH2)3-
-(R)-CH2CHOHCH2-
-(R)-CH2CHOHCH2-
3,4,5-(MeO)3Bn-
Bn-
a
Overall yields from alkylated amino esters 2a−f. Following secondary amines treatment with BTC, resulting activated compounds were treated with
N′-alkyl/aryl tert-butyl carbazate either in CH2Cl2 or in THF.
was envisaged by solid-phase activation of secondary amine
before addition of an excess of carbazate, as previously described
for the solid-phase urea formation.27 Resin 13 was then treated
with BTC, 2,4,6-collidine in THF for 30 min before addition of a
10-fold excess of carbazate 6a. After one night stirring at room
temperature, the resin was washed, dried and treated with a 95%
TFA/H2O mixture for 1 h. The LC-MS analysis of the crude
material indicated the presence of triazinedione 16a together
with unreacted secondary amine. Unexpectedly, no trace of
uncyclized semicarbazide was detected suggesting that the con-
version of the resin-bound semicarbazide 15 to triazinedione 16a
was quantitative during the final acidic treatment at room tem-
perature. This promising result led us to optimize various para-
meters of the reaction such as the nature of the solvent (CH2Cl2,
1,2-dichloroethane (DCE), THF), the nature of the base
To the best of our knowledge, the solid-phase semi-
carbazide cyclization initiated in highly acidic conditions has
not been described. Apart from the work of Obreza10 and our
solution-phase study herein described, the reaction between
hydrazine derivatives and electrophilic ester bond proceeds in
basic conditions.28 Here, an acidic treatment at room
temperature for one hour enabled a one-pot three-step process
i.e. semicarbazide deprotection followed by the concomitant
cyclization/release to provide trisubstituted triazinedione. It is
noteworthy that the cyclization did not proceed when R2 = H
(Scheme 4). In this case, the disubstituted triazinedione 16b
was isolated in a very low 3% yield, whereas the corresponding
linear semicarbazide 18 was obtained in 62% yield. Similarly,
the influence of the N-alkylation of the primary amine upon the
cyclization has been previously reported for the synthesis of
thiohydantoins.29
(Hunig’s base, Et N, Pyridine/4-dimethylaminopyridine
̈
3
(DMAP)) and the temperature (rt, 40 °C, 70 °C, microwave
(μw)). Both the temperature of the reaction and the nature of
the solvent were found crucial to drive the semicarbazide forma-
tion to completion. Indeed, following secondary amine activation
with BTC, the resin treated with an excess of carbazate 6a in
CH2Cl2 at room temperature provided triazinedione 16a in 15%
yield, whereas in THF the yield reached 33% overall for the six-
step solid-phase process. The reaction performed overnight at
70 °C in THF further increased the yield up to 61%. Finally, best
We also investigated the possibility to prepare D-triazinediones
starting from the Fmoc-D-amino acid-Wang-PS resins (Figure 2).
According to the same protocol and starting from Fmoc-D-
phenylanine-Wang-PS resin, D-triazinedione 19 was obtained
in a comparable 54% yield with optical rotation of opposite
value compared to L-triazinedione 16a (−24.9 vs +28.0,
respectively).
With optimized conditions in hand, the scope of our solid-
phase methodology was demonstrated by the synthesis of a
small library (Table 5) starting from various Fmoc-L-amino
acids such as Phe, Leu, Ser(tBu), Glu(tBu), Lys(Boc). Resin 12
was reacted with benzaldehyde, isovaleraldehyde, Boc-amino-
ethanal, 3,5-dimethoxybenzaldehyde, p-nitrobenzaldehyde and
results were obtained with Hunig’s base over the other bases
̈
evaluated. Isolated triazinedione 16a was fully characterized by
1H, 13C, and 2D NMR techniques (HSQC, HMBC and NOESY
experiments) and high-resolution mass spectrometry (HRMS).
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Table 4. Solution-Phase Cyclization Towards Aza-DKP 4a−w
a
yield (%)
b
c
compound
R1
R2
R3
method A
method B
4a
4b
4c
4d
4e
4f
HOCH2-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Ph-
72
(CH3)2CHCH2-
(CH3)2CHCH2-
(CH3)2CHCH2-
(CH3)2CHCH2-
Bn-
48
d
nd
nd
4-MeOBn-
4-MeOBn-
4-NO2Bn-
43
4-NO2Bn-
Bn-
66
38
59
4g
4h
4i
Bn-
Bn-
CH3(CH2)4-
3,4,5-(MeO)3Bn-
Bn-
2-indoleCH2-
-(CH2)3-
Bn-
40
58
28
55
4j
-(CH2)3-
3,4,5-(MeO)3Bn-
2-furanCH2-
2-thiopheneCH2-
2-MeOBn-
3-MeOBn-
3,5-(MeO)2Bn-
2,4,6-(MeO)3Bn-
2-BrBn-
4k
4l
-(CH2)3-
nd
nd
20
50
66
nd
65
50
19
nd
21
63
44
-(CH2)3-
4m
4n
4o
4p
4q
4r
-(CH2)3-
-(CH2)3-
-(CH2)3-
-(CH2)3-
-(CH2)3-
-(CH2)3-
3-BrBn-
4s
4t
-(CH2)3-
4-BrBn-
-(CH2)3-
4-MeOBn-
4-NO2Bn-
4u
4v
4w
-(CH2)3-
-(R)-CH2CHOHCH2-
-(R)-CH2CHOHCH2-
3,4,5-(MeO)3Bn-
Bn-
a
b
c
Isolated yield starting from protected semicarbazides 3a−w. Method A: p-TsOH, toluene, reflux, 2.5 h. Method B: Amberlyst 15 resin, MeOH,
d
μwave 150 W, 120−140 °C, 15−20 min. Not detected by LC-MS.
a
Scheme 3. Solid-Phase Strategy Towards Aza-DKP 16a−p
Scheme 4. Influence of the N-Alkylation upon the
Cyclization
a
Reagents and conditions: (i) 20% piperidine/DMF; (ii) aldehyde or
ketone, TMOF, NaBH3CN, AcOH 1%; (iii) BTC, Et3N, CH2Cl2; (iv)
R3-NHNHBoc, THF, 70 °C, overnight.
cyclohexanone to form the corresponding imines that were
reduced in presence of NaBH3CN and 1% AcOH. Following
activation of the secondary amines 13 with BTC, the
semicarbazide formation was performed in presence of various
carbazates N-alkylated with Bn-, isopentyl-, p-nitrobenzyl-, and
propargyl moieties at 70 °C in THF, overnight. The final
deprotection, cleavage and cyclization were initiated in pre-
sence of a TFA/water (95/5) mixture for 1 h at rt. In all cases,
triazinediones were obtained in >60% purity (HPLC analysis,
UV detection at 220 nm) and in yields ranging from 9 to 78%
for the 6 steps. These results show that the process herein
developed is compatible with the presence of hydrophobic,
Figure 2. Synthesis of L- and D-triazinediones 16a and 19.
polar, cationic or anionic aminoacids (Table 5, compounds
16a−e), neutral, electron-rich, and aliphatic aldehydes (Table
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Table 5. Representative 2,4,5-Trisubstituted-1,2,4-triazine-3,6-diones 16a−o, 4b, and c-[Aza-Phe-Pro] 4i Synthesized from
Fmoc-L-amino Acid Wang-PS Resins
a
b
c
compound
R1
R2
R3
mass [M + H]+
tR, (min)
HPLC (%)
yield (%)
16a
16b
16c
16d
16e
16f
16g
16h
16i
16j
16k
16l
Bn-
Bn-
Bn-
H-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
386.47
296.34
326.37
368.41
366.47
366.48
339.41
446.52
431.47
378.49
366.48
431.47
334.39
354.14
355.36
352.45
Bn-
11.4
8.1
94
<10
91
61
3
HOCH2-
Bn-
Bn-
Bn-
7.7
37
57
35
48
25
9
HOOC(CH2)2-
8.1
91
NH2(CH2)4-
6.8
90
Bn-
(CH3)2CH(CH2)2-
NH2-(CH2)2-
3,5-(MeO)2Bn-
p-NO2Bn-
c-C6H11-
Bn-
11.7
6.9
90
Bn-
65
Bn-
11.5
11.3
11.8
11.7
11.4
9.9
62
Bn-
75
34
26
67
37
50
47
54
63
78
Bn-
60
Bn-
(CH3)2CH(CH2)2-
90
Bn-
Bn-
p-NO2Bn-
77
16m
16n
16o
4b
Bn-
Bn-
91
Bn-
Bn-
HOOC−CH2-
10.7
7.5
84
Me-
p-NO2Bn-
Bn-
Bn-
Bn-
Bn-
88
(CH3)2CHCH2-
-(CH2)3-
11.5
6.4
>98
>98
4i
a
Retention times from analytical RP-HPLC profile (UV detection at 220 nm, see Supporting Information for HPLC experimental conditions).
Determined by RP-HPLC analysis of the crude product. Isolated yield based on manufacturer’s loading of Fmoc-L-aminoacid Wang resin.
b
c
Table 6. Triazinediones Obtained Starting from HMBA-PS Resin Following a Final Cyclative-Release Step
compound
R1
R2
R3
HPLC (%)
yield (%)
a
b
a
b
16a
16f
16h
16i
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
Bn-
94 /99
61 /93
(CH3)2CH(CH2)2-
3,5-(MeO)2C6H3CH2-
p-NO2C6H5CH2-
90/96
62/96
75/95
48/57
9/53
34/62
a
b
Wang-PS resin. HMBA-PS resin.
5, compounds 16f−i) but also cyclohexanone (Table 5, com-
pound 16j). The propargyl derived triazinedione 16m could be
further functionalized by CuI-catalyzed-1,3-dipolar cycloaddi-
tion (“Click chemistry”) to provide new chemical entities
containing a 1,2,3-triazole ring.30−33 Carboxylic acid derived
triazinedione 16o could be also readily functionalized by coupl-
ing reaction with commercially available amine building blocks
to increase further the molecular and structural diversity of the
compounds. The successful synthesis of compound 4i shows
that the strategy is also efficient to rapidly access c-[aza-Phe-
Pro] analogues and represents a straightforward alternative to
the solution-phase strategies already described in the litera-
ture.10,15 Interestingly, the comparison of the yields obtained
for triazinediones 4b and 4i by both strategies highlighted the
efficacy of the solid-phase approach (23 and 33% in solution
respectively versus 63% and 78% on solid-phase).
To improve further the purity of the crude triazinediones,
we envisaged the use of an acid-stable linker. The potential
side-products formed during the synthesis (bis-alkylated com-
pounds or secondary amines) would then be expected to remain
attached to the resin while the desired product is released
by intramolecular cyclization. This cyclative-release process
has already been advantageously considered for the synthesis
of potential bioactive compounds such as DKP,4 hydantoin,14
or tetrahydro-β-carbolinehydantoin34 scaffolds on various resins.
Figure 3. RP-HPLC profiles of triazinedione 16h obtained
either on (A) Wang or (B) HMBA resins. Chromatographic
conditions: C18 Symmetry Shield column (4.6 × 150 mm). Flow
rate 1 mL.min−1. Buffer A: 0.1% aqueous TFA. Buffer B: 0.1% TFA
in CH3CN. Gradient: 0−100% B over 20 min. Detection at
220 nm.
328
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ACS Combinatorial Science
Research Article
resin represents a convenient and efficient entry to highly pure
triazinediones.
Triazinedione 16o Conformational Analysis by X-ray and
1H NMR. Single-crystal X-ray analysis of triazinedione 16o
enabled the determination of both the conformation of the
scaffold and also the spatial arrangement of the side chains. The
ORTEP diagram (Figure 4) shows that the six-membered
heterocyclic ring adopts a pseudo boat conformation. The C2−
C3−N2−N3 atoms are planar whereas N3−C1−N1−C2
display a torsion angle of −33 °C. The methyl group C4 (R1
substituent) is oriented pseudoaxial in the same side of the
plane as the benzyl group at N3 (R3 substituent), but slightly
displaced from each other. The pseudoquatorial hydrogen at
C2 displays the same spatial orientation as the p-nitrobenzyl
group at N1 (R2 group).
Figure 4. ORTEP view of compounds 16o (displacement ellipsoids at
the 50% probability level).
1
Figure 5 shows the H NMR spectrum of triazinedione 16o
in various deuterated solvents and temperature. In CDCl3
at 298 K, benzyl protons featured an AB quartet for H6a,b
(ΔδAB = 0.11, JAB = 15.2 Hz) and an AX pattern centered at
4.89 ppm and 4.17 ppm for H5a,b (Δppm =0.72, JAX = 15.9 Hz).
When recorded in a CDCl3/MeOD (1:1) mixture, both H5a,b
The final cyclization was generally initiated under basic con-
ditions and not in highly acidic medium such as TFA.
Synthesis on HMBA-PS Resin. The potential of our approach
was evaluated on 4-Hydromethyl benzoic acid-polystyrene
(HMBA-PS) resin which was esterified with Fmoc-L-Phe-OH
using the symmetrical anhydride method.35 Following Fmoc
resin loading determination,36 the same protocol that was
developed on Wang resin was applied for the synthesis of repre-
sentative compounds 16a, f, h, i. Resin-bound semicarbazides
were treated in TFA/water (95:5) mixture for 3 h. As observed on
Wang resin, in such acidic conditions, all the target triazinediones
were released in solution. As expected, the cyclative-release pro-
cess ensured better purities than those obtained on Wang resin
(Table 6).
Figure 3 shows the RP-HPLC profiles of crude compound
16h obtained either on Wang (A) or HMBA (B) resins
enabling the improvement of the purity from 62% to 96%, respec-
tively. Unexpectedly, yields were also increased significantly for all
compounds (Table 6). Thus, the strategy developed on HMBA
and H6a,b resonated as an AX system (Δppm =0.71/0.68, JAX
=
15.3/15.8 Hz respectively) with slight modification of their
chemical shifts compared to those in CDCl3. In DMSO-d6, the
peaks were line broadening at 298 K but were found sharper
and better resolved with increasing temperature. At 390 K,
diastereotopic benzyl protons H5a,b and H6a,b displayed also
an AX system (Δppm =0.45/0.48, JAX = 15.4/15.9 Hz res-
pectively) and did not give rise to the coalescence of the signal.
The pseudoequatorial H2 proton came up as a quadruplet (J =
6.9 Hz). Both the solvents and temperature had a very limited
influence on its chemical shift indicating that no changing in
the scaffold conformation occurred. Altogether, these results
indicate that in protic and/or polar solvents, regardless of the
temperature, triazinedione 16o is a rather rigid and constrained
structure with hindered rotation about the phenyl-CH2 bonds.
1
Figure 5. H NMR spectrum of 16o in various deuterated solvents.
329
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ACS Combinatorial Science
Research Article
separated and the organics were washed with brine (20 mL),
CONCLUSION
■
saturated NaHCO3
(20 mL), and brine (20 mL). The
(aq)
In conclusion, we have described in this paper a solution-phase
approach toward a set of novel aza-DKP, both c-[aza-alkylGly-
Pro] derivatives and 2,4,5-trisubstituted-1,2,4-triazine-3,
6-diones. The solid-phase approach enabled a rapid access to
triazinediones in good yields and high purities. The efficiency of
the method makes this approach readily amenable to the
parallel synthesis of structurally diverse collections of aza-DKP
and will facilitate the evaluation of this underprivileged scaffold
for potential interesting biological activity.
organic layers were dried over MgSO4, filtered and the solvent
was removed in vacuo. The residues were redissolved in
methanol (10 mL) and NaOH
(2N, 10 mL) and stirred
(aq)
for 2 h. The solvent was removed in vacuo and the residues
redissolved in ethyl acetate (50 mL). The organics were washed
with brine (2 × 20 mL) and dried over MgSO4. The solvent
was removed in vacuo to give the crude products.
General Procedure for the Solution-Phase Synthesis
of Semicarbazides 3a−3w. A solution of the alkyl hydrazine
carboxylic acid tert-butyl ester (1.51 mmol, 2.25 equiv) and
diisopropyl ethylamine (1.68 mmol, 2.50 equiv) in tetrahy-
drofuran or dichloromethane (5 mL) was added dropwise to a
stirred solution of triphosgene (0.67 mmol, 1.00 equiv in dry
tetrahydrofuran or dichloromethane (5 mL). After it was stirred
for 5 min, a solution of amino acid methyl ester (1.51 mmol,
2.25 equiv) and diisopropyl ethylamine (1.68 mmol, 2.50 equiv) in
tetrahydrofuran or dichloromethane (5 mL) was added in one-
portion. The reaction mixture was stirred at room temperature for
a further 10 min before the solvent was removed in vacuo. The
crude product was rapidly purified by column chromatography
(10−100% ethyl acetate/hexane) to give the title semicarbazide as
a mixture of rotamers.
General Procedure for the Solution-Phase Synthesis
of 1,2,4-Triazine-3,6-diones 4a−4w. Semicarbazide
(0.43 mmol, 1.0 equiv) and p-toluene sulfonic acid hydrate
(0.65 mmol, 1.5 equiv) were dissolved in toluene (10 mL). The
reaction mixture was heated to reflux and after stirring for 30−
40 min was allowed to cool to room temperature. The solvent was
removed in vacuo and the crude product was purified by column
chromatography (50−100% ethyl acetate/hexane) to give the title
1,2,4-triazine-3,6-dione.
EXPERIMENTAL PROCEDURES
■
General Methods. Reagents were obtained from commer-
cial sources and used without any further purification. Fmoc-
protected amino acid loaded on Wang resin were purchased
from Aldrich and the overall yields for the solid-phase syntheses
of aza-DKPs were calculated based on the initial loadings
provided by the supplier. Solid-phase reactions conducted at
room temperature were performed in polypropylene tubes
equipped with polyethylene frits and polypropylene caps using
an orbital agitator shaking device. Solid-phase reactions at
70 °C were conducted in sealed glassware tubes using the
Chemflex rotating oven from Robbins Scientific as the shaking
device. Thin-layer chromatography was performed on silica gel
60F254 plates. Flash chromatography was performed on silica
gel (40 μm, Grace) or RP18 (25−40 μm, Merck) prepacked
columns on a SpotII ultima from Armen. 1H NMR spectra were
recorded at 200, 300, and 500 MHz on a Bruker Advance
spectrometer. Chemical shifts are reported in parts per million
(ppm), coupling constants (J) are reported in hertz (Hz).
Signals are described as s (singlet), d (doublet), t (triplet), m
(multiplet), and brs (broad singlet). LC-MS spectra were
obtained on a ZQ (Z quadripole) Waters/Micromass spectro-
meter equipped with an X-Terra C18 column (4.6 × 50 mm,
3.5 μm) using electrospray ionization mode (ESI). Analytical
HPLC analyses were performed on a Chromolith SpeedROD
column (50 × 4.6 mm, C18) from Merck using the following
conditions: flow rate 7 mL.min−1. Buffer A: 0.1% aqueous TFA.
Buffer B: 0.1% TFA in CH3CN. Gradient: 0% B in 1 min than
0−100% B over 5 min. Detection at 220/254 nm. Retention
times (tR) from analytical RP-HPLC are reported in minutes.
General Procedure for the Synthesis of N′-Alkylidene-
tert-butyl Carbazates 5a−5p. A solution of tert-butylcarba-
zate (15.0 mmol, 1.0 equiv) and the aldehyde (16.5 mmol, 1.1
equiv) in toluene (10 mL) was stirred at 50 °C for 40 min. The
reaction mixture was allowed to cool to room temperature
overnight and the crude product crystallized out of solution.
The product was then filtered, washed with excess cold toluene
and dried in vacuo (where the product did not crystallize out of
solution the solvent was removed in vacuo to give the crude
product). The crude product was recrystallized.
(S)-2,4-Dibenzyl-5-(hydroxymethyl)-1,2,4-triazine-3,6-
1
dione 4a. Colorless oil. [α]D +14.2 (c 0.3, MeOH). H NMR
(300 MHz, CDCl3) δ 7.34−7.26 (m, 10H), 5.08 (d, 1H, J =
15.1 Hz), 4.91 (d, 1H, J = 15.1 Hz), 4.52 (d, 1H, J = 15.1 Hz),
4.20 (d, 1H, J = 15.1 Hz), 3.76−3.70 (m, 3H), 2.56 (br s 1H).
13C NMR (75 MHz, CDCl3) δ 164.2, 154.8, 136.3, 134.8,
129.1, 128.8, 128.3, 128.2, 60.5, 60.1, 53.3, 49.2. HRMS: calcd
for C18H20N3O3 326.14284, found 326.15012.
(S)-2,4-Dibenzyl-5-isobutyl-[1,2,4]triazine-3,6-dione 4b.
1
White solid. mp 124−126 °C [α]D +21° (c 1.4, CHCl3). H
NMR (400 MHz, CDCl3) δ 7.37−7.27 (m, 10H), 5.04 (d, 1H,
J = 15.2 Hz), 4.72 (AB, 2H, Δδ = 0.44, J = 14.8 Hz), 4.05
(d, 1H, J = 15.2 Hz), 3.62 (dd, 1H, J = 6.4 Hz), 1.58−1.54
(m, 1H), 1.28−1.23 (m, 2H), 0.79 (dd, 6H, J = 6.4 Hz). 13C
NMR (100 MHz, CDCl3) δ 166.1, 154.1, 136.4, 135.1, 128.9,
128.8, 128.3, 128.1, 127.9, 57.3, 51.2, 49.38.7, 24.4, 23.0, 21.8.
MS (ESI) m/z 352.4 [M + H+].
(S)-2-(4-Methoxy-benzyl)-4-benzyl-5-isobutyl-[1,2,4]-
triazine-3,6-dione 4d. Colorless oil. [α]D +16.4 (c 0.8, CHCl3).
1H NMR (300 MHz, CDCl3) δ 8.28 (br s, 1H), 7.34−7.27 (m,
7H), 6.87−6.85 (m, 2H), 5.02 (d, 1H, J = 15.0 Hz), 4.72 (d,
1H, J = 15.0 Hz), 4.59 (d, 1H, J = 15.0 Hz), 4.05 (d, 1H, J =
15.0 Hz), 3.80 (s, 3H), 3.62 (m, 1H), 1.61−1.24 (m, 3H, m)
0.82 (d, 3H, J = 6.6 Hz), 0.78 (d, 3H, J = 6.6 Hz). 13C NMR
(75 MHz, CDCl3) δ 166.1, 159.9, 154.5, 136.6, 130.4, 129.0,
128.3, 128.1, 127.0, 114.5, 57.6, 55.4, 51.1, 49.5, 38.9, 24.6,
23.2, 21.9. MS (ESI) m/z 382.0 [M + H+].
General Procedure for the Synthesis of N′-Alkyl-tert-
butyl Carbazates 6a−6p. N′-Hydrazone-carboxylic acid tert-
butyl esters (10 mmol, 1.0 equiv) and sodium cyanoborohy-
dride (25 mmol, 2.5 equiv) were suspended in tetrahydrofuran
(10 mL). Acetic acid (2 mL) was added and the reaction
mixtures stirred at room temperature overnight. In two specific
cases, 5d and 5e, p-toluene-sulfonic acid was used instead of
acetic acid and the reaction mixtures were refluxed for 4 h.
All reactions were then concentrated in vacuo, ethyl acetate
(20 mL), and water (20 mL) were added to the reaction
mixture, followed by solid NaHCO3 until basic. The layers were
(S)-2-(4-Methoxybenzyl)-4-(4-nitrobenzyl)-5-isobutyl-
1,2,4-triazine-3,6-dione 4e. White crystalline solid. mp 128−
130 °C (Ethyl acetate/hexane). [α]D +10.4 (c 0.4, CHCl3). 1H
330
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ACS Combinatorial Science
Research Article
NMR (400 MHz, CDCl3) δ 8.22−8.20 (m, 2H), 7.47−7.45 (m,
2H), 7.28−7.26 (m, 2H), 6.89−6.87 (m, 2H), 5.09 (d, 1H, J =
15.6 Hz), 4.70 (d, 1H, J = 15.1 Hz), 4.64 (d, 1H, J = 15.1 Hz),
4.14 (d, 1H, J = 15.6 Hz), 3.81 (s, 3H), 3.63 (dd, 1H, J = 9.5,
5.5 Hz), 1.39−1.24 (m, 3H), 0.86 (d, 3H, J = 6.5 Hz), 0.81 (d,
3H, J = 6.5 Hz). 13C NMR (100 MHz, CDCl3) δ 165.6, 160.1,
154.3, 147.8, 144.4, 130.4, 128.7, 126.6, 124.3, 114.6, 58.9,
55.5, 51.1, 49.3, 39.1, 24.7, 23.1, 22.0. MS (ESI) m/z 449.0
[M + Na+].
c-[Aza-3-methoxyphenylalaninyl-prolyl] 4n. White crystal-
line solid. mp 170−171 °C. [α]D −25.4 (c 0.5, CHCl3). H
1
NMR (400 MHz, CDCl3) δ 8.18 (br s, 1H), 7.28−7.23 (m,
1H), 6.93−6.83 (m, 3H), 4.66 (s, 2H), 3.89 (t, 1H, J = 8.0 Hz),
3.79 (s, 3H), 3.54 (t, 2H, J = 7.0 Hz), 2.27−2.10 (m, 2H),
2.05−1.85 (m, 2H). 13C NMR (75 MHz, CDCl3) δ 166.4,
160.1, 154.3, 136.7, 129.9, 120.8, 114.2, 113.8, 57.7, 55.3, 50.6,
45.3, 26.8, 23.4.MS (ESI) 276.2 [M + H+].
c-[Aza-3,5-dimethoxyphenylalaninyl-prolyl] 4o. Colorless
oil. [α]D −9.2 (c 1.6, MeOH,). 1H NMR (400 MHz, CDCl3) δ
8.35 (br s, 1H), 6.50 (d, 2H, J = 2.1 Hz), 6.39 (t, 1H, J = 2.1
Hz), 4.64 (d, 1H, J = 15.4 Hz), 4.59 (d, 1H, J = 15.4 Hz), 3.91
(t, 1H, J = 8.0 Hz), 3.77 (s, 6H), 3.54 (t, 2H, J = 7.0 Hz), 2.28−
2.09 (m, 2H), 2.04−1.85 (m, 2H). 13C NMR (75 MHz,
CDCl3) δ 166.3, 161.2, 154.2, 136.6, 106.5, 100.0, 57.7, 55.3,
50.6, 45.2, 26.8, 23.3. MS (ESI) m/z 306.1 [M + H+].
(S)-2-(4-Nitrobenzyl)-4,5-dibenzyl-1,2,4-triazine-3,6-dione
1
4f. Colorless oil. [α]D −105.6 (c 0.7, MeOH). H NMR (300
MHz, CDCl3) δ 9.12 (br s, 1H), 8.13−8.10 (m, 2H), 7.36 −
7.07 (m, 12H), 5.11 (d, 1H, J = 15.4 Hz), 4.52 (d, 1H, J = 15.4
Hz), 3.97−3.86 (m, 3H), 2.96 (dd, 1H, J = 13.9, 5.1 Hz), 2.85
(dd, 1H, J = 13.9, 5.5 Hz). 13C NMR (75 MHz, CDCl3) δ
164.7, 153.4, 148.7, 142.8, 135.9, 135.1, 129.9, 129.3, 129.1,
129.0, 128.4, 127.7, 124.0, 60.0, 51.2, 49.4, 35.9. MS (ESI) m/z
431.0 [M + H+].
c-[Aza-2-bromophenylalaninyl-prolyl] 4p. Yellow oil [α]D
−33.2 (c 0.5, CHCl3). 1H NMR (300 MHz, CDCl3) δ 8.15 (br
s, 1H), 7.59 (dd, 1H, J = 7.6, 1.0 Hz), 7.39 (dd, 1H, J = 7.6, 1.6
Hz), 7.20 (td, 1H, J = 7.6, 1.0), 7.10 (td, 1H, J = 7.6, 1.6 Hz),
5.01 (d, 1H, J = 15.7 Hz), 4.69 (d, 1H, J = 15.7 Hz), 3.97
(t, 1H, J = 7.7 Hz), 3.56 (t, 2H, J = 6.2 Hz), 2.17−2.10 (m,
2H), 2.10−1.86 (m, 2H). 13C NMR (75 MHz, CDCl3) δ 166.4,
154.2, 134.8, 133.2, 130.3, 129.8, 127.9, 123.9, 57.7, 50.4, 45.3,
26.7, 23.4. MS (ESI) m/z 348.0, 346.0 ([M + Na+], 1:1 ratio).
c-[Aza-3-bromophenylalaninyl-prolyl] 4q. White crystal-
(S)-4,5-Dibenzyl-2-pentyl-1,2,4-triazine-3,6-dione 4g. Col-
1
orless oil. [α]D +15.5 (c 0.2, CHCl3). H NMR (400 MHz,
CDCl3) δ 7.27−7.19 (m, 6H), 7.10−7.08 (m, 4H), 4.97 (d, 1H,
J = 15.1 Hz), 3.90 (dd, 1H, J = 6.5, 5.5 Hz), 3.60 (d, 1H, J =
15.1 Hz), 3.15−3.10 (m, 2H), 2.96 (dd, 1H, J = 14.1, 5.5 Hz),
2.87 (dd, 1H, J = 14.1, 6.5 Hz), 1.46−1.31 (m, 2H), 1.25−1.15
(m, 4H), 0.82 (t, 3H, J = 7.3 Hz). 13C NMR (100 MHz,
CDCl3) δ 165.0, 153.5, 136.4, 135.6, 129.8, 129.0, 128.9, 128.3,
128.1, 127.5, 60.2, 49.4, 47.9, 35.8, 28.8, 26.9, 22.4, 14.1. MS
(ESI) m/z 366.0 [M + H+].
1
line solid. mp 236−237 °C. [α]D −6.0 (c 0.5, DMSO). H
NMR (400 MHz, DMSO-d6) δ 10.75 (br s, 1H), 7.80 (m, 2H),
7.64 (m, 2H), 5.19 (d, 1H, J = 16.6 Hz), 4.61 (d, 1H, J = 16.6
Hz), 4.38 (m, 2H), 4.28 (t, 1H, J = 7.8 Hz), 2.44−2.14 (m,
4H). 13C NMR (100 MHz, DMSO-d6) δ 203.8, 181.2, 137.8,
134.2, 130.8, 130.6, 126.9, 121.6, 59.8, 48.8, 44.9, 28.9, 22.9.
MS (ESI) m/z 348.0, 346.0 ([M + Na+], 1:1 ratio).
(S)-5-(1H-Indol-2-ylmethyl)-2-(3,4,5-trimethoxy-benzyl)-4-
benzyl-1,2,4-triazine-3,6-dione 4h. Crystalline white solid. mp
1
82−84 °C. [α]D +34.4 (c 0.9, MeOH). H NMR (300 MHz,
CDCl3) δ 8.38 (br s, 1H), 7.54 (d, 1H, J = 6.0 Hz), 7.36−6.99
(m, 9H), 5.97 (s, 2H), 5.11 (d, 1H, J = 14.6 Hz), 4.45 (d, 1H,
J = 14.1 Hz), 4.00−3.95 (m, 2H), 3.70 (s, 3H) and 3.67
(s, 6H), 3.23 (dd, 1H, J = 15.0, 4.0 Hz), 3.09 (dd, 1H, J = 15.0,
5.0 Hz), 2.18 (d, 1H, J = 14.1 Hz). 13C NMR (75 MHz,
CDCl3) δ 174.1, 165.2, 153.7, 136.3, 136.1, 129.3, 129.1, 128.5,
128.2, 124.5, 122.5, 120.1, 119.4, 111.5, 109.0, 106.0, 60.9, 59.3,
56.3, 52.8, 49.2, 25.9. MS (ESI) m/z 515.0 [M + H+].
c-[Aza-4-bromophenylalaninyl-prolyl] 4r. Colorless oil.
1
[α]D +50.5 (c 0.5, DMSO). H NMR (400 MHz, DMSO-d6)
δ 10.43 (br s, 1H), 7.53 (d, 2H, J = 8.4 Hz), 7.23 (d, 2H, J = 8.4
Hz), 4.86 (d, 1H, J = 15.3 Hz), 4.23 (d, 1H, J = 15.3 Hz), 3.93
(t, 1H, J = 7.9 Hz), 3.39−3.34 (m, 2H), 2.07−1.86 (m, 4H).
13C NMR (100 MHz, DMSO-d6) δ 166.2, 154.7, 147.3, 145.8,
129.1, 123.9, 57.6, 49.0, 45.2, 27.2, 23.2. MS (ESI) m/z 324.0,
322.0 ([M + H+], 1:1 ratio).
c-[Aza-phenylalaninyl-prolyl] 4i. White solid. mp 220−221
1
°C. [α]D −45° (c 1.1, chloroform). H NMR (400 MHz,
CDCl3) δ 7.36−7.33 (m, 5H), 4.69 (s, 2H), 3.88 (t, 1H, J =
8.0 Hz), 3.57−3.53 (m, 2H), 2.22−2.14 (m, 2H), 2.01−1.93
(m, 2H). 13C NMR (100 MHz, CDCl3) δ 166.4, 154.3, 135.1,
128.9, 128.5, 128.3, 57.6, 50.6, 45.2, 26.7, 23.3. MS (ESI) m/z
246.5 [M + H+].
c-[Aza-4-nitrophenylalaninyl-prolyl] 4u. White crystalline
1
solid. mp 200−201 °C. [α]D −6.0 (c 0.5, DMSO). H NMR
(400 MHz, DMSO-d6) δ 10.51 (br s, 1H), 8.21 (d, 2H, J =
8.8 Hz), 7.57 (d, 2H, J = 8.8 Hz), 5.01 (d, 1H, J = 16.5 Hz),
4.44 (d, 1H, J = 16.5 Hz), 4.03 (t, 1H, J = 7.3 Hz), 3.40−3.36
(m, 2H), 2.11−1.85 (m, 4H). 13C NMR (100 MHz, DMSO-d6)
δ 170.6, 162.1, 157.9, 152.1, 134.0, 128.8, 54.3, 53.9, 50.1, 31.9,
28.0. MS (ESI) m/z 291.1 [M + H+].
c-[Aza-3,4,5-trimethoxyphenylalaninyl-prolyl] 4j. Crystal-
line green solid. mp 270−271 °C. [α]D −56.8 (c 0.5, CHCl3).
1H NMR (400 MHz, CDCl3) δ 7.72 (br s, 1H), 6.60 (s, 2H),
4.77 (d, 1H, J = 14.8 Hz), 4.46 (d, 1H, J = 14.8 Hz), 3.92
(t, 1H, J = 7.9 Hz), 3.85 (s, 9H), 3.58−3.53 (m, 2H), 2.25−
2.16 (m, 2H), 2.03 − 2.94 (m, 2H). 13C NMR (75 MHz,
CDCl3) δ 166.6, 154.5, 153.8, 130.6, 106.1, 60.8, 57.9, 56.4,
51.1, 45.4, 26.9, 23.5. MS (ESI) m/z 336.1 [M + H+].
c-[Aza-2-methoxyphenylalaninyl-prolyl] 4m. Colorless oil.
c-[Aza-3,4,5-trimethoxyphenylalaninyl-trans-4-hydroxy-
1
prolyl] 4v. Colorless oil. [α]D −87.5 (c 0.1, CHCl3). H NMR
(400 MHz, CDCl3) δ 6.59 (s, 2H), 4.81 (d, 1H, J = 15.1 Hz),
4.59 (t, 1H, J = 4.5 Hz), 4.43 (d, 1H, J = 15.1 Hz), 4.30 − 4.26
(m, 1H), 3.85 (s, 9H), 3.72−3.71 (m, 1H), 3.63−3.60 (m, 1H),
2.35−2.23 (m, 1H), 2.23−2.11 (m, 1H), 1.25 (s, 1H). 13C
NMR (100 MHz, CDCl3) δ 166.6, 153.7, 138.2, 130.4, 115.1,
105.9, 69.4, 60.8, 56.8 56.2, 54.0, 51.2, 36.5. MS (ESI) m/z
352.1 [M + H+].
1
[α]D +14.0 (c 0.5, MeOH). H NMR (400 MHz, CDCl3) δ
8.04 (br s, 1H), 7.25 (dd, 1H, J = 7.5, 1.5 Hz), 7.25 (ddd, 1H,
J = 8.0, 7.5, 2.0 Hz), 6.97−6.80 (m, 2H), 4.66 (d, 1H, J = 15.0
Hz), 4.59 (d, 1H, J = 15.0 Hz), 3.90−3.75 (m, 4H), 3.46−3.41
(m, 2H), 2.28−1.99 (m, 2H), 1.94−1.75 (m, 2H). 13C NMR
(75 MHz, CDCl3) δ 164.4, 156.2, 153.2, 131.4, 129.0, 122.7,
120.6, 109.7, 56.7, 54.8, 44.3, 44.2, 26.0, 22.3. MS (ESI) m/z
276.1 [M + H+].
c-[Aza-phenylalaninyl-trans-4-hydroxyprolyl] 4w. Color-
less crystalline solid. mp 126−128 °C. [α]D −48.8 (c 0.4,
1
CHCl3). H NMR (300 MHz, CDCl3) δ 7.48−7.27 (m, 5H),
4.83 (d, 1H, J = 15.0 Hz), 4.65−4.51 (m, 1H), 4.27 (dd, 1H, J =
10.6, 7.0 Hz), 3.72 (dd, 1H, J = 12.1, 4.4 Hz), 3.62 (dd, 1H, J =
331
dx.doi.org/10.1021/co300015k | ACS Comb. Sci. 2012, 14, 323−334

ACS Combinatorial Science
Research Article
12.1, 2.9 Hz), 2.36−2.06 (m, 2H), 1.88 (br s, 1H). 13C NMR
(100 MHz, CDCl3) δ 166.6, 154.2, 134.9, 129.0, 128.5, 69.4,
56.4, 54.1, 50.7, 36.5. MS (ESI) m/z 262.1 [M + H+].
(S)-3-(2,4-Dibenzyl-3,6-dioxo-1,2,4-triazinan-5-yl)-
propanoic acid 16d. White solid. mp 75 −77 °C. [α]D +52.8°
(c 1.6, chloroform). 1H NMR (400 MHz, CDCl3) δ 7.40−7.28
(m, 10H), 6.97 (sl, 2H), 5.06 (d, 1H, J = 15.2 Hz), 4.73 (AB,
2H, Δδ = 0.20, J = 15.2 Hz), 4.11 (d, 1H, J = 14.8 Hz),), 3.75
(dd, 1H, J = 8.8,O 4.4 Hz), 2.35 (t, 2H, J = 6.8 Hz), 2.01−1.94
(m, 1H), 1.89−1.84 (m, 1H). 13C NMR (100 MHz, CDCl3)
δ 176.7, 164.7, 153.3, 136.1, 134.7, 128.9, 128.8, 128.7,
128.4, 128.1, 57.8, 51.3, 49.0, 29.2, 24.0. MS (ESI) m/z 368.4
[M + H+].
(S)-5-(4-aminobutyl)-2,4-dibenzyl-1,2,4]triazine-3,6-dione
16e. Clear oil. [α]D +64.5° (c 1.1, chloroform). 1H NMR (400
MHz, CDCl3) δ 7.83 (bs, 2H),7.32−7.22 (m, 10H), 7.13 (sl,
1H), 4.91 (d, 1H, J = 15.2 Hz), 4.70 (AB, 2H, Δδ = 0.20, J =
15.2 Hz), 4.05 (d, 1H, J = 15.2 Hz),), 3.59 (dd, 1H, J = 8.4, 4.8
Hz), 2.72 (bs, 2H), 1.45−1.14 (m, 6H). 13C NMR (100 MHz,
CDCl3) δ 153.5, 136.2, 135.1, 128.9, 128.7, 128.6, 128.3, 128.0,
58.5, 51.2, 49.2, 39.3, 29.0, 26.6, 21.3. MS (ESI) m/z 367.5
[M + H+].
General Procedure for the Solid-Phase Synthesis of
1,2,4-Triazine-3,6-diones. The Fmoc-protected amino acid
(∼ 70 μmol), loaded on Wang or HMBA resin, was swollen in
DCM for 1 h. The solution was drained and a 20% solution of
piperidine in DMF (1.5 mL) was added. The mixture was
shaken at room temperature for 15 min. The solution was
drained and the deprotection step repeated once. The solution
was drained and the resin was successively washed with DMF,
DCM, DMF, and anhydrous TMOF. The resin was swollen in
anhydrous TMOF (1.5 mL) and the aldehyde (10 equiv) was
added. The mixture was shaken at room temperature for
90 min. The solution was drained and the resin washed with
anhydrous TMOF. The resin was swollen in anhydrous TMOF
and sodium cyanoborohydride (10 equiv) was added. The
mixture was shaken at room temperature for 15 min then acetic
acid (10 equiv) was added and the mixture was further shaken
at room temperature for 1 h. The solution was drained and the
resin was successively washed with methanol (3×), DCM, and
THF. The resin was swollen in anhydrous THF (1.5 mL),
2,4,6-collidine (10 equiv) and BTC (10 equiv) were added, and
the mixture was shaken at room temperature for 30 min. The
solution was drained and the resin was successively washed with
anhydrous THF, anhydrous DCM, anhydrous THF and ether.
The resin was placed in a microwave tube and a solution of the
N′-alkylhydrazine-carboxylic acid tert-butyl ester (10 equiv) in
anhydrous THF (1.5 mL) was added. The tube was sealed and
the mixture shaken at 70 °C overnight. The mixture was
filtrated and the resin successively washed with DCM,
methanol, and ether. TFA/water: 95/5 (1.2 mL) was added
to the resin and the mixture was shaken at room temperature
for 1 h. The mixture was filtrated and the filtrate evaporated in
vacuo. The crude product was purified by RP chromatography.
(S)-2,4,5-Tribenzyl-[1,2,4]triazine-3,6-dione 16a. White
solid. mp 65−66 °C. [α]D −24.4° (c 1, chloroform). 1H
NMR (400 MHz, CDCl3) δ 7.39−7.13 (m, 9H), 7.24−7.2 (m,
4H), 7.12 (d, 2H, J = 4.8 Hz), 5.1 (d,1H, J = 14.8 Hz), 4.55 (d,
1H, J = 14.8 Hz), 3.97 (X of ABX, 1H, J = 5.6 Hz), 3.84 (d, 1H,
J = 14.8 Hz), 3.79 (d, 1H, J = 14.8 Hz), 2.85 (AB of ABX, 2H,
JAB = 14.0 Hz, JAX = 6.0 Hz, JBX = 5.2 Hz). 13C NMR (100
MHz, CDCl3) δ 164.7, 153.5, 135.7, 135.1, 134.3, 12937, 129,
128.9, 128.8, 128.7, 128.6, 128.2, 128.1, 127.5, 59.8, 51.8, 19.4,
35.9. HRMS: calcd for C24H24N3O2 386.17522, found
386.18655.
(S)-2,5-Dibenzyl-4-isopentyl-[1,2,4]triazine-3,6-dione 16f.
1
Clear oil. [α]D −33.9° (c 1.1, chloroform). H NMR (400
MHz, CDCl3) δ 7.37−7.28 (m, 6H), 7.23−7.20 (m, 2H), 7.13
(dd, 2H, J = 6.8, 1.6 Hz), 4.16 (AB, 2H, Δδ = 0.7, J = 14.8 Hz),
4.03 (X of ABX, 1H, J = 6.0 Hz), 3.88−3.81 (m, 1H), 2.89 (AB
of ABX, 2H, JAB = 13.6 Hz, JAX = 6.4 Hz, JBX = 5.2 Hz), 2.63−
2.57 (m, 1H), 1.54−1.51 (m, 1H), 1.44−1.37 (m, 2H), 0.90−
0.87 (m, 6H) . 13C NMR (100 MHz, CDCl3) δ 164.8, 153.4,
135.1, 134.6, 129.7, 128.9, 128.8, 128.7, 128.4, 127.4, 61.2,
51.5, 44.7, 36.7, 36.4, 25.7, 22.5, 22.2. MS (ESI) m/z 366.5
[M + H+].
(S)-4-(2-aminoethyl)-2,5-dibenzyl-[1,2,4]triazine-3,6-dione
16g. White solid. mp 95−96 °C. [α]D −76.9° (c 1,
1
chloroform). H NMR (400 MHz, CDCl3) δ 7.85 (sl, 2H),
7.37−7.19 (m, 8H), 6.93 (d, 2H, J = 6.7 Hz), 4.87 (d, 1H, J =
14.8 Hz), 4.11−4.07 (m, 2H), 3.85 (m, 1H), 3.78 (d, 1H, J =
14.8 Hz), 3.03−3.00 (m, 1H), 2.86−2.85 (m, 1H), 2.64−2.59
(m, 2H), 2.53−2.47 (m, 1H) . 13C NMR (100 MHz, CDCl3) δ
164.9, 153.5, 135.2, 135.0, 129.4, 128.8, 128.4, 127.3, 63.1, 50.8,
45.0, 38.2, 36.4, 31.2. MS (ESI) m/z 339.4 [M + H+].
(S)-2,5-Dibenzyl-4-(3,5-dimethoxybenzyl)-[1,2,4]triazine-
3,6-dione 16h. White solid. mp 56−57 °C. [α]D −18.1° (c 1.8,
1
chloroform). H NMR (400 MHz, CDCl3) δ 7.37−7.31 (m,
7H), 7.24−7.21 (m, 2H), 7.14 (d, 2H, J = 6.8 Hz), 6.38 (t, 1H,
J = 4.4 Hz), 6.35 (d, 2H, J = 2.4 Hz), 5.05 (d, 1H, J = 15.2 Hz),
4.62 (d, 1H, J = 14.4 Hz), 4.00 (X of ABX, 1H, J = 5.6 Hz),
3.76 (s, 6H), 3.73 (d, 1H, J = 11.6 Hz), 3.69 (d, 1H, J = 11.2
Hz), 2.89 (AB of ABX, 2H, JAB = 14.0 Hz, JAX = 6.4 Hz, JBX
=
(S)-2,5-Dibenzyl-[1,2,4]triazine-3,6-dione 16b. White solid.
5.6 Hz). 13C NMR (100 MHz, CDCl3) δ 164.4, 161.2, 153.6,
138.1, 135.2, 134.3, 129.8, 129.0, 128.8, 128.7, 128.6, 127.5,
106.2, 99.8, 59.8, 55.3, 51.8, 49.3, 35.9. MS (ESI) m/z 446.5
[M + H+].
1
mp 216−218 °C. [α]D −94.8° (c 1.1, chloroform). H NMR
(400 MHz, CDCl3) δ 7.28−7.16 (m, 8H), 7.09 (d, 2H, J = 6.8
Hz), 4.38 (AB, 2H, Δδ = 0.09, J = 15.2 Hz), 3.92 (X of ABX,
1H, J = 4 Hz), 2.76 (AB of ABX, 2H, JAB = 14.0 Hz, JAX = 8.4
Hz, JBX = 4.4 Hz). 13C NMR (100 MHz, CDCl3) δ 153.8,
135.2, 134.9, 129.4, 128.7, 128.6, 128.1, 128.0, 127.1, 55.8, 50.5,
38.3. MS (ESI) m/z 296.3 [M + H+].
(S)-2,5-Dibenzyl-4-(4-nitrobenzyl)-[1,2,4]triazine-3,6-dione
16i. White solid. mp 73−74 °C. [α]D +32.7° (c 1, chloroform).
1H NMR (400 MHz, CDCl3) δ 8.21−8.17 (m, 2H), 7.41−7.32
(m, 8H), 7.26−7.23 (m, 2H), 7.15 (dd, 2H, J = 6.8, 1.6 Hz),
5.13 (d, 1H, J = 15.6 Hz), 4.26 (AB, 2H, Δδ = 0.72, J =
14.8 Hz), 3.97 (X of ABX, 1H, J = 4.8 Hz), 3.78 (d, 1H, J =
16.0 Hz), 2.90 (AB of ABX, 2H, JAB = 13.6 Hz, JAX = 6.8 Hz,
JBX = 4.4 Hz). 13C NMR (100 MHz, CDCl3) δ 164.4, 153.3,
147.7, 143.6, 134.8, 133.9, 129.6, 129.1, 129.0, 128.8, 128.7,
128.6, 127.7, 124.1, 61.2, 51.7, 49.1, 36.2. MS (ESI) m/z 431.5
[M + H+].
(S)-2,4-Dibenzyl-5-(hydroxymethyl)-[1,2,4]triazine-3,6-
dione 16c. Clear oil. [α]D −8.1° (c 0.9, chloroform). 1H NMR
(400 MHz, CDCl3) δ 7.36−7.26 (m, 10H), 5.10 (d, 2H, J =
14.8 Hz), 4.85 (d, 1H, J = 14.8 Hz), 4.55 (d, 1H, J = 14.8 Hz),),
4.16 (d, 1H, J = 15.2 Hz), 3.76−3.73 (m, 3H). 13C NMR (100
MHz, CDCl3) δ 164.2, 154.5, 135.9, 134.6, 129.0, 128.9, 128.6,
128.4, 128.1, 60.3, 59.9, 52.9, 49.0. MS (ESI) m/z 326.4
[M + H+].
332
dx.doi.org/10.1021/co300015k | ACS Comb. Sci. 2012, 14, 323−334

ACS Combinatorial Science
Research Article
(S)-4-Cyclohexyl-2,5-dibenzyl-[1,2,4]triazine-3,6-dione 16j.
White solid. mp 78−79 °C. [α]D +70.2° (c 1.1, chloroform). 1H
NMR (400 MHz, CDCl3) δ 7.37−7.23 (m, 8H), 7.11 (m, 2H),
4.20 (AB, 2H, Δδ = 0.74, J = 14.8 Hz), 4.07 (X of ABX, 1H, J =
12.8 Hz), 4.03 (m, 1H), 2.92 (AB of ABX, 2H, JAB = 13.6 Hz,
JAX = 8.4 Hz, JBX = 6.4 Hz), 1.97 (m, 1H), 1.83 (m, 2H), 1.67
(m, 2H), 1.41 (m, 4H), 1.11 (m, 1H). 13C NMR (100 MHz,
CDCl3) δ 165.3, 153.8, 135.2, 134.6, 129.6, 129.0, 128.8, 128.6,
128.5, 127.3, 57.4, 55.9, 50.9, 38.6, 32.2, 31.4, 26.0, 25.7, 25.3.
MS (ESI) m/z 378.5 [M + H+].
(S)-4,5-Dibenzyl-2-isopentyl-[1,2,4]triazine-3,6-dione 16k.
White solid. mp 89−90 °C. [α]D +14.8° (c 1.3, chloroform). 1H
NMR (400 MHz, CDCl3) δ 7.37−7.22 (m, 6H), 7.17 (d, 4H,
J = 7.2 Hz), 5.07 (d, 1H, J = 14.8 Hz), 3.98 (X of ABX, 1H, J =
6.0 Hz), 3.69 (d, 1H, J = 15.2 Hz), 3.33−3.17 (m, 2H), 2.99
(AB of ABX, 2H, JAB = 13.6 Hz, JAX = 6.4 Hz, JBX = 4.8 Hz),
1.56−1.50 (m, 1H), 1.39−1.32 (m, 1H), 1.30−1.22 (m, 1H),
0.89 (dd, 6H, J = 6.0, 1.6 Hz). 13C NMR (100 MHz, CDCl3) δ
165.0, 153.0, 136.1, 135.3, 129.6, 128.9, 128.8, 128.2, 127.9,
127.4, 59.8, 49.1, 46.0, 35.6, 35.5, 25.6, 22.3. MS (ESI) m/z
366.5 [M + H+].
ASSOCIATED CONTENT
* Supporting Information
Experimental data for compounds 2a−2f, 5a−5p, 6a−6p, 7, 8,
9, 10, general experimental procedure for the synthesis of
N-alkyl-amino acid methyl esters, 2D NMR data (HSQC, HMBC
and NOESY experiments) for compound 16a, X-ray crystallo-
graphic data of compound 16o. This material is available free of
charge via Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*Phone: +33(0)368 85 4236 (D.B.); +44(0)1603 597154
(A.G.). Fax: +33(0)368 85 4310 (D.B.); +44 (0)1603592003
(A.G.). Email: dominique.bonnet@unistra.fr (D.B.); A.
Ganesan@uea.ac.uk (A.G.).
■
Funding
This work was supported by Maybridge and the French
“Ministere de la Recherche”, ANR, CNRS, Region Alsace and
̀ ́
Strasbourg University.
Notes
The authors declare no competing financial interest.
(S)-2-(4-nitrobenzyl)-4,5-dibenzyl-[1,2,4]triazine-3,6-dione
16l. White solid. mp 207−208 °C. [α]D −25.5° (c 1.1,
ACKNOWLEDGMENTS
■
1
chloroform). H NMR (400 MHz, CDCl3) δ 8.15 (d, 2H, J =
We thank Dr. Denis Heissler for helpful discussions, Pascale
Buisine and Dr. Patrick Wehrung for MS analyses, Cyril
Antheaume for NMR analyses as well as Dr. Lydia Brelot
(Service de Crystallographie, Institut de Chimie de Strasbourg)
for the X-ray analysis.
8.8 Hz), 7.38−7.29 (m, 8H), 7.23 (m, 2H), 7.11 (m, 2H), 5.11
(d, 1H, J = 15.2 Hz), 4.52 (d, 1H, J = 16.0 Hz), 3.98 (X of
ABX, 1H, J = 5.2 Hz), 3.90−3.83 (m, 2H), 2.91 (AB of ABX,
2H, JAB = 14.0 Hz, JAX = 5.6 Hz, JBX = 5.2 Hz). 13C NMR (100
MHz, CDCl3) δ 157.4, 151.4, 147.3, 139.6, 139.0, 133.6, 132.8,
132.7, 132.6, 132.1, 132.0, 131.4, 127.7, 63.6, 54.8, 39.7. MS
(ESI) m/z 431.5 [M + H+].
(S)-4,5-Dibenzyl-2-(prop-2-yn-1-yl)-[1,2,4]triazine-3,6-
dione 16m. Clear oil [α]D −12.9° (c 1, chloroform). 1H NMR
(400 MHz, CDCl3) δ 7.39−7.27 (m, 6H), 7.18 (d, 4H, J = 6.8
Hz), 6.61 (sl, 1H), 5.02 (d, 1H, J = 15.2 Hz), 4.26 (dd, 1H, J =
17.6, 2.4 Hz), 4.02 (X of ABX, 1H, J = 6.4 Hz), 3.75 (d, 1H, J =
14.8 Hz), 3.43 (dd, 1H, J = 17.6, 2.4 Hz), 3.04 (AB of ABX, 2H,
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A. M.; Hatley, R. J. D.; Irving, W. R.; Livermore, D. G.; Miller, N. D.;
Nerozzi, F.; Sollis, S. L.; Szardenings, A. K. 2,5-Diketopiperazines as
potent and selective oxytocin antagonists1: Identification, stereo-
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(9) Evans, B. E.; Rittle, K. E.; Bock, M. G.; Dipardo, R. M.;
Freidinger, R. M.; Whitter, W. L.; Lundell, G. F.; Veber, D. F.;
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J
AB = 13.6 Hz, JAX = 6.4 Hz, JBX = 5.2 Hz), 2.33 (dd, 1H, J = 4.8,
2.8 Hz) . 13C NMR (100 MHz, CDCl3) δ 165.0, 153.1, 135.5,
135.0, 129.7, 129.0, 128.9, 128.2, 128.1, 127.5, 60.0, 49.4, 37.8,
36.2. MS (ESI) m/z 334.4 [M + H+].
(S)-2-(4,5-Dibenzyl-3,6-dioxo-1,2,4-triazinan-2-yl)acetic
acid 16n. White solid. mp 96 °C. [α]D +11.9° (c 1,
1
chloroform). H NMR (400 MHz, CDCl3) δ 7.37−7.30 (m,
6H), 7.21 (d, 2H, J = 7.6 Hz), 7.15 (d, 2H, J = 8.4 Hz), 5.78
(bs, 3H), 5.01 (A of AX, d, 1H, JAX = 14.8 Hz), 4.23 (A′ of A′X′,
d, 1H, J = 18.0 Hz), 4.04 (t, 1H, J = 7.6 Hz), 3.85 (X of AX,
d, 1H, JAX = 14.8 Hz), 3.10 (X′ of A′X′, d, 1H, J = 18.0 Hz),
3.02−3.00 (bs, 2H). 13C NMR (100 MHz, CDCl3) δ 172.2,
165.9, 153.6, 135.3, 134.8, 129.8, 129.0, 128.9, 128.3, 127.7,
59.8, 49.5, 48.4, 35.6. MS (ESI) m/z 400.5 [M + H+].
(S)-2-Benzyl-5-methyl-4-(4-nitrobenzyl)-[1,2,4]triazine-3,6-
dione 16o. White solid. mp 171−172 °C. [α]D +72.1° (c 1,
1
chloroform). H NMR (400 MHz, CDCl3) δ 8.10 (d, 2H, J =
8.6 Hz), 7.37 (d, 2H, J = 8.6 Hz), 7.26−7.22 (m, 4H), 7.15
(s, 1H), 4.89 (A of AX, d, 1H, JAX = 15.9 Hz), 4.65 (AB, 2H,
ΔδAB = 0.11, JAB = 15.2 Hz), 4.17 (X of AX, d, 1H, JAX
=
15.9 Hz), 3.64 (q, 1H, J = 7.0 Hz), 1.07 (d, 3H, J = 7.0 Hz). 13C
NMR (100 MHz, CDCl3) δ 166.0, 154.1, 147.9, 144.5, 134.8,
129.2, 128.9, 128.8, 124.3, 55.9, 51.7, 48.7, 15.1. MS (ESI) m/z
355.0 [M + H+].
333
dx.doi.org/10.1021/co300015k | ACS Comb. Sci. 2012, 14, 323−334

ACS Combinatorial Science
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