Microwave-assisted diastereoselective two-step three-component synthesis for rapid access to drug-like libraries of substituted 3-amino-β-lactams

Article abstract of DOI:10.1016/j.bmc.2017.11.014

Large, diverse compound libraries are an essential requisite in target-based drug development. In this work, a robust microwave-assisted synthesis for the diastereoselective generation of 3-saccharinyl-trans-β-lactams is reported. The method is optimised

Full text of DOI:10.1016/j.bmc.2017.11.014

Bioorganic & Medicinal Chemistry 26 (2018) 41–49
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Microwave-assisted diastereoselective two-step three-component
synthesis for rapid access to drug-like libraries of substituted
3-amino-b-lactams
Guido V. Janssen a,b, Joyce A.C. van den Heuvel c, Rik P. Megens c, Jorg C.J. Benningshof c, Huib Ovaa a,b,
⇑
a Department of Chemical Immunology, Leiden University Medical Center, Albinusdreef 2, NL-2333 ZA Leiden, The Netherlands
b Division of Cell Biology, Netherlands Cancer Institute, Plesmanlaan 121, NL-1066 CX Amsterdam, The Netherlands
c Mercachem, Kerkenbos 1013, NL-6546 BB Nijmegen, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Article history:
Large, diverse compound libraries are an essential requisite in target-based drug development. In this
work, a robust microwave-assisted synthesis for the diastereoselective generation of 3-saccharinyl-
trans-b-lactams is reported. The method is optimised for combinatorial library synthesis in which deco-
ration of the scaffold is varied on both the b-lactam and the saccharine moiety. Within the European Lead
Factory (ELF) consortium, a library of 263 compounds was efficiently produced using the developed
methodology.
Received 25 September 2017
Revised 3 November 2017
Accepted 8 November 2017
Available online 16 November 2017
Keywords:
b-Lactams
Library synthesis
Staudinger reaction
Microwave synthesis
Saccharines
Ó 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://
creativecommons.org/licenses/by/4.0/).
1. Introduction
rine has, next to being an artificial sweetener, also found applica-
tion in medicinal chemistry. For example as inhibitor for tumour-
The identification of lead compounds in drug discovery relies
heavily on high throughput screening of large collections of com-
pounds to a biological target for a desired effect. Structural diver-
sity in these collections is mainly limited to planar scaffolds. 3D-
complexity, which has been proven to be an important element
in drug discovery,1 is mainly enhanced by combining a planar core
with substituents.2 While there is an increasing trend in the devel-
opment of scaffolds that contain more 3D elements, the synthetic
tractability of these scaffolds diminishes.
associated carbonic anhydrase IX and XII,12,13 inhibitor for inter-
feron-mediated inflammation14 and as antidiarrheal agents by
activation of the
l
opioid receptor.15 Thereby, the combination of
these two functionalities renders a chemical entity with great bio-
logical potential.
The perpendicular orientation of the two ring systems, together
with the substituents that we aim to introduce on the sp3 back-
bone of the b-lactam provide the non-planar elements in this scaf-
fold. For functionalization, three diversification points are
envisioned on the scaffold. R1 is envisioned as proton or nitro-
group, of which the latter can be reduced to the amine 4c and sub-
sequently be acylated to increase the diversity (4d, Scheme 1A).
The two remaining diversity points are R2 and R3 that are intro-
duced by choosing the appropriate imine.
Several syntheses are known for b-lactams of which the Stau-
dinger reaction, in which an in-situ formed ketene is reacted with
an imine, is the most frequently used (Scheme 1B).16 Usually acid
chlorides are used as ketene precursors in the Staudinger reac-
tion.17 However, these reactive species are less suitable for use in
parallel synthesis. Therefore we envisioned in-situ activation of 1
to intermediate 3 using Mukaiyama’s salt as a more convenient
approach.18 Although the synthesis of the proposed scaffold using
the Staudinger reaction using Mukaiyama’s salt has been described
Within the European Lead Factory (ELF) consortium,3–5 we aim
to develop libraries of lead-like compounds that have a high
molecular complexity and that are synthesized from easily accessi-
ble building blocks in a minimum number of steps. In this work, we
present a scaffold that consists of a saccharine moiety that is con-
nected to a b-lactam via its amide-nitrogen atom (4, Scheme 1A)
and that can be synthesized in a single step.6 The b-lactam core
is a frequently found structural motif in antibiotics7 targeting the
cell wall synthesis by blocking the action of transpeptidases8–10
and it is useful as a building block in organic chemistry.11 Saccha-
⇑
Corresponding author at: Department of Chemical Immunology, Leiden Univer-
sity Medical Center, Albinusdreef 2, NL-2333 ZA Leiden, The Netherlands.
E-mail address: h.ovaa@lumc.nl (H. Ovaa).
https://doi.org/10.1016/j.bmc.2017.11.014
0968-0896/Ó 2017 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

42
G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
(Table 1, entry 1).19 Refluxing 1a, 2a, and 10 in CH2Cl2 with Et3N as
base for 16 h was equally effective since 11a was obtained in a
comparable yield (82%) and diastereoselectivity (cis/trans < 5:95,
entry 2).
Unfortunately, amide 12 was quantatively obtained when ben-
zaldehyde 9 and aniline 8 were used in a one-pot reaction instead
of using imine 2a, (entry 3). This can be explained by the fact that
imine formation is slow compared to the acid activation and amide
formation between the amine and the activated acid. Conse-
quently, this necessitates the use of pre-formed imines in the reac-
tion. The reaction time was reduced dramatically from 16 h to 10
min using a microwave. The reaction of 1a and 2a in a microwave
at 100 °C for 30 or 10 min afforded 11a in 87% and 86% yield
respectively, selectively trans (entries 4–5).
With optimised conditions (Table 1, entry 5) established, we
explored the scope of the reaction with acetic acid 1a (R1 = H)
and a variety of imines 2b–2j (Table 2). Electron withdrawing as
well as electron donating aromatic rings on the R2- and R3-position
afforded the products in selectively trans configuration 11b–11h in
moderate yields after preparative HPLC/MS20 (30–50%; Table 2,
entries 1–7). However, the reactions of aliphatic imines 2i and 2j,
derived from neohexanal and n-hexanal, resulted in mixtures of
unidentified products (entries 8 and 9). While R3 is thus limited
to aromatic rings, the reaction with imines derived from isopropy-
lamine afforded the desired products 11k–11m in reasonable
yields (63–32%), but not with full diastereoselectivity (cis/trans
15:85–33:67, entries 10–12).21 The reactions with 4-aminomethyl-
pyridine and b-alanine derived imines 2n and 2o further empha-
sise the fact that N-aliphatic imines are more challenging
substrates because the reaction with 2n did not afford any product
and with imine 2o product 11o is obtained in only a minimal yield
of 8% (entries 13 and 14). Finally, 6-nitrosaccharinyl acetic acid 2b
could be used without difficulties in the reaction with imines 2c
and 2b affording 11p and 11q in acceptable yields of 58 and 61%
respectively as single diastereomers (entries 15 and 16).
Scheme 1. (A) General scheme for the Staudinger reaction; (B) approach for the
synthesis of scaffold 4.
before,6 the scope of the reaction has not been thoroughly exam-
ined. Moreover, due to the fact that a stepwise addition of reagents
is required, this method is impractical for use in the combinatorial
synthesis of a large number of analogues.
In this report we present the optimisation of the reported pro-
cedure for the combinatorial synthesis of tri-substituted b-lactams,
expand the scope of the reaction and show its applicability by pro-
ducing a 263 compound library using the optimised method.
2. Results and discussion
Having established the scope of the reaction for R2 and R3, we
were also interested to see if it would be possible to use substi-
tuted acetic acids other than 1. Phthaloyl glycine 13 and theo-
phylline-7-acetic acid 14 proved good substrates for the reaction
and gave access to 18 and 19 respectively in good yields (89 and
65%) with full diastereoselectivity (Table 3, entries 1 and 2). Imida-
zol-4-acetic acid 15 and indomethacine 16 on the other hand,
failed to react and resulted in mixtures of unidentified products
(entries 3 and 4). To investigate whether this is caused by the less
electron withdrawing properties of the aromatic systems con-
nected to the acetic acid part, we tested the moderately electron
poor p-nitrophenyl acetic acid 17 (entry 5). Indeed this acetic acid
did not afford the product and consequently more electron poor
acetic acids are required.
We started with the synthesis of saccharinylacetic acid 1a by
reacting potassium saccharine 5a and bromoacetic acid 6 neat for
4 h at 110 °C to afford 1a in 85% yield (Scheme 2A). Unfortunately,
the potassium salt of 6-nitrosaccharine 5b was unreactive under
the same conditions. We therefore resorted to a two-step synthesis
in which 5b is reacted with methyl bromoacetate 7 at 70 °C in DMF
for 4 h after which the crude methyl ester is hydrolysed in concen-
trated HCl to yield 1b in 55% yield over two steps without the need
for purification (Scheme 2B).
For optimisation of the Staudinger reaction, we selected saccha-
rinyl acetic acid 1a and imine 2a as benchmark substrates. In the
initial experiment we reacted 1a with Mukaiyama’s salt 10 in CH2-
Cl2 for 8 h at reflux, followed by the addition of imine 2a and Et3N
which was refluxed for 16 h. This afforded the desired b-lactam
11a in 85% yield with excellent diastereoselectivity (cis/trans <
5:95) according to 1H NMR analysis of the crude reaction mixture
We next turned our attention to modification of the nitro group
of compounds 11p and 11q (Scheme 3). Reduction to the amine
Scheme 2. Synthesis of saccharine acetic acids 1a and 1b.

G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
43
Table 1
Optimisation of the conditions for the benchmark reaction.
Entry
Imine or amine/aldehyde
Conditions
d.r. (cis/trans)a
Yield 11a (%)b
Yield 12 (%)b
1
2
3
4
5
2a
2a
8 & 9
2a
2a
1a & 10 reflux 8 h, then 2a and Et3N
Reflux 16 h
Reflux 16 h
100 °C, microwave, 30 min
100 °C, microwave, 10 min
<5:95
<5:95
–
<5:95
<5:95
85
82
–
87
86
–
–
Quant.
–
–
a
Determined by 1H NMR analysis of the crude reaction mixture.
Yield of isolated product.
b
Table 2
Investigation of the reaction scope for the imine.
Entry
Acetic acid
R1
Imine
R2
R3
d.r.a
Yield (%)b
Product
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
H
H
H
H
H
H
H
H
H
H
H
H
H
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
4-BrC6H4
4-BrC6H4
4-BrC6H4
3-OMeC6H4
3-OMeC6H4
3-OMeC6H4
Phenyl
4-BrC6H4
3-OMeC6H4
i-Propyl
4-OMeC6H4
4-MeC6H4
3-NO2C6H4
4-OMeC6H4
4-MeC6H4
3-NO2C6H4
2-Pyrrole
Neohexyl
n-Hexyl
4-OMeC6H4
4-MeC6H4
3-NO2C6H4
4-MeC6H4
<5:95
<5:95
<5:95
<5:95
<5:95
<5:95
<5:95
–
42
50
25
40
40
30
35
–
11b
11c
11d
11e
11f
11g
11h
11i
11j
11k
11l
11m
11n
9
–
–
10
11
12
13
15:85
33:67
15:85
–
63
32
51
–
i-Propyl
i-Propyl
14
1a
H
2o
4-MeC6H4
<5:95
8
11o
15
16
1b
1b
NO2
NO2
2c
2b
4-BrC6H4
4-BrC6H4
4-MeC6H4
4-OMeC6H4
<5:95
<5:95
58
61
11p
11q
a
Determined by 1H NMR analysis of the crude reaction mixture.
Yield of isolated product.
b
and subsequent amidation using acid chlorides can further
increase the diversity potential of the scaffold. Reduction of 11p
and 11q was quantitatively achieved by treatment with iron in
acetic acid for 3 h at room temperature to afford 23a and 23b.
The acylated amines 24a and 24b were obtained in good yields
when the amines 23 were treated with acetyl chloride and sodium
bicarbonate in THF, illustrating the applicability of the
functionalization.
purification of the final products by preparative LC/MS, 263 com-
pounds were isolated with a purity over 85% (LC/MS), which corre-
sponds to a success rate of 75%. These compounds were added to
the Joint European Compound Library.
3. Conclusions
With the chemistry established, we enumerated a library of 349
compounds with an average cLogP of 3.6 and average molecular
weight of 502 (Chart 1).22 For production of the library, large
batches of saccharinyl acetic acids 1a (187 mmol, 45.0 g) and 1b
(143 mmol, 41.6 g) were prepared using the same methods as dur-
ing optimisation. Subsequently, the appropriate imines (2) were
pre-formed and reacted with 1a, 10 and Et3N in CH2Cl2.23 After
In conclusion, we have developed a rapid, efficient microwave-
assisted synthesis of 3-amino-b-lactams, suitable for the combina-
torial synthesis of 3-saccharinyl-b-lactams starting from substi-
tuted acetic acids. The resulting 3-amino-b-lactams were isolated
in reasonable yields and excellent diastereoselectivity using a
range of different imines and substituted acetic acids. We have
shown the application of the obtained b-lactams in follow-up

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G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
Table 3
Investigation of the reaction scope for the acetic acid.
Entry
1
Acetic acid
d.r. (cis/trans)a
Yield (%)b
89
Product
<5:95
18
2
<5:95
65
19
3
4
–
–
–
–
20
21
5
–
–
22
a
Determined by 1H NMR analysis of the crude reaction mixture.
Yield of isolated product.
b
4
2
0
400
450
500
550
Molecular weight
Chart 1. Physiochemical properties plot (MW vs. cLogP) for the library compounds:
green dots 349 enumerated compounds; orange dots 263 produced compounds.
Scheme 3. Functionalisation of the saccharine moiety (R1).
described as s (singlet), d (doublet), t (triplet), q (quartet), br (broad
singlet) and m (multiplet) or combinations thereof. Electrospray
Ionization (ESI) high-resolution mass spectrometry was carried
out using a Waters Xevo G2 XS QTOF instrument in positive ion
mode (capillary potential of 3000 V). Flash chromatography was
chemistry, and the developed methodology was used to produce a
263 compound library.
4. Experimental
performed on Grace Davisil Silica Gel (particle size 40–63 lm, pore
4.1. General experimental details
diameter 60 Å) using the indicated eluent. Thin Layer Chromatog-
raphy (TLC) was performed using TLC plates from Merck (SiO2,
Kieselgel 60 F254 neutral, on aluminium with fluorescence indica-
tor) and compounds were visualized by UV detection (254 nm)
unless mentioned otherwise. Microwave reactions were performed
in a Biotage Initiator+ using the corresponding microwave vials.
Reversed phase preparative HPLC/MS was carried out on a
Waters AutoPurification system equipped with a Waters 2998 pho-
All commercially available reagents and solvents were used as
purchased. Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker Avance 300 (75.00 MHz for 13C) using the
residual solvent as internal standard (1H: d 7.26 ppm, 13C{1H}: d
77.00 ppm for CDCl3), Chemical shifts (d) are given in ppm and
coupling constants (J) are quoted in hertz (Hz). Resonances are

G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
45
todiode array detector, Waters 3100 mass detector and a Waters
2767 sample manager using preparative Waters X-bridge C18
rine acetic acid methyl ester was suspended in HCl (30 mL, 37% in
water) and heated to 100 °C for 4 h after which the hydrolysis was
complete. After cooling to r.t., the mixture was diluted with water
and the precipitated carboxylic acid was filtered to yield (1b) as a
Bordeaux-reddish solid (1.81 g, 55%). 1H NMR (300 MHz, DMSO) d
(ppm) = 13.44 (bs, 1H), 9.32 (d, J = 1.8 Hz, 1H), 8.74 (dd, J = 8.4, 2.0
Hz, 1H), 8.39 (d, J = 8.4 Hz, 1H), 4.56 (s, 2H).
l
m
(30 mm  150 mm or 19 mm  150 mm) column using water ace-
tonitrile mixtures containing 0.1% TFA.
4.2. Synthetic procedures
4.2.1. General procedures
General procedure A, synthesis of the imines. To a vial containing
toluene were added aldehyde (1.0 equiv) and amine (1.0 equiv) fol-
lowed by MgSO4. The mixture was allowed to be stirred overnight
after which it was filtered and evaporated to dryness. The imines
were used in the cycloaddition without further purification.
4.2.4. (E)-N-(4-Bromophenyl)-1-(p-tolyl)methanimine (2b)
2b was synthesized according to general procedure A from 4-
methylbenzaldehyde and 4-bromoaniline to yield a brownish crys-
talline solid. 1H NMR (300 MHz, CDCl3) d (ppm) = 8.31 (s, 1H),
7.82–7.74 (m, 2H), 7.54–7.45 (m, 2H), 7.33–7.26 (m, 2H), 7.13–
7.00 (m, 2H), 2.43 (s, 3H).
General procedure B, cycloaddition.
A microwave vial was
charged with dichloromethane the appropriate imine (1.0 equiv),
saccharinyl acetic acid (1.0 equiv), Mukaiyama’s salt (1.05 equiv)
and triethylamine (2 equiv). The mixture was heated for 10 min
in the microwave at 100 °C. After the reaction, the mixture was
concentrated in vacuo and purified on a preparative LCMS. Waters
X-Bridge 30 mm  150 mm C18 column; gradient, CH3CN:H2O
(0.1% TFA). Fractions containing the product were automatically
collected based on observed mass and UV-signal after which they
were lyophilized to obtain the pure products.
General procedure C, nitro reduction. A roundbottomed flask was
charged with the required nitro saccharinyl b-lactam that was dis-
solved in glacial acetic acid. Next iron (10 equiv) was added and
the suspension was stirred for 3 h at room temperature. After com-
pletion of the reaction (TLC) the mixture was diluted with ethyl
acetate and neutralized with saturated NaHCO3 solution. The water
layer was extracted three times with EtOAc. The organic layers
were combined, washed with brine, dried over Na2SO4 and concen-
trated in vacuo.
4.2.5. (E)-N-(4-Bromophenyl)-1-(4-methoxyphenyl)methanimine (2c)
2c was synthesized according to general procedure A from 4-
methoxybenzaldehyde and 4-bromoaniline to yield a yellow crys-
talline solid. 1H NMR (300 MHz, CDCl3) d (ppm) = 8.35 (s, 1H),
7.90–7.77 (m, 2H), 7.53–7.44 (m, 2H), 7.12–7.03 (m, 2H), 7.02–
6.94 (m, 2H), 3.88 (s, 3H).
4.2.6. (E)-N-(4-Bromophenyl)-1-(3-nitrophenyl)methanimine (2d)
2d was synthesized according to general procedure A from 3-
nitro benzaldehyde and 4-bromoaniline to yield a yellow crys-
talline solid. 1H NMR (300 MHz, CDCl3) d (ppm) = 8.79–8.71 (m,
1H), 8.53 (s, 1H), 8.34 (ddd, J = 8.1, 2.3, 1.1 Hz, 1H), 8.24 (dt, J =
7.7, 1.2 Hz, 1H), 7.67 (t, J = 8.1 Hz, 1H), 7.60–7.49 (m, 2H), 7.19–
7.08 (m 2H).
4.2.7. (E)-N-(3-Methoxyphenyl)-1-(4-methoxyphenyl)methanimine
(2e)
General procedure D, Library production. In an 8 mL screw cap
vial a solution of amine (0.1 mmol, 1 equiv) and aldehyde (0.1
mmol, 1 equiv) in dry toluene (1 mL) was prepared. Subsequently
MgSO4 (approx. 100 mg) was added. The resulting mixtures were
stirred overnight. The mixtures were filtered and the filtrate was
concentrated to afford the imines. The imine was used in the next
step immediately without purification. To the imines was added 2
mL of a stock solution containing the appropriate saccharinylacetic
acid in CH2Cl2 (0.05 mM ꢀ 0.1 mmol, 1 equiv). Subsequently, 2-
chloro-1-methylpyridin-1-ium iodide (Mukaiyama’s salt) (0.105
mmol, 1.05 equiv) and triethylamine (0.22 mmol, 2.2 equiv) were
added. The resulting mixtures were overnight heated at 45 °C in
closed vials. The mixtures were washed with water (1 mL) after
which the organic layers were evaporated. The crude mixtures
were purified by preparative HPLC (acetonitrile/water mixtures
containing 0.1% TFA). The product containing fractions were lyo-
philized to afford the pure products.
2e was synthesized according to general procedure A from 4-
methoxy benzaldehyde and 3-methoxyaniline to yield a pale yel-
low crystalline solid. 1H NMR (300 MHz, CDCl3) d (ppm) = 8.39 (s,
1H), 7.91–7.80 (m, 2H), 7.34–7.11 (m, 3H), 7.04–6.93 (m, 2H),
6.82–7.71 (m, 3H), 3.88 (s, 3H), 3.84 (s, 3H).
4.2.8. (E)-N-(3-methoxyphenyl)-1-(p-tolyl)methanimine (2f)
2f was synthesized according to general procedure A from 4-
methyl benzaldehyde and 3-methoxyaniline to yield a brown oil.
1H NMR (300 MHz, CDCl3) d (ppm) = 8.42 (s, 1H), 7.84–7.73 (m,
2H), 7.34–7.21 (m, 3H), 6.84–6.72 (m, 3H), 3.84 (s, 3H), 2.42 (s, 3H).
4.2.9. (E)-N-(3-methoxyphenyl)-1-(3-nitrophenyl)methanimine (2g)
2g was synthesized according to general procedure A from 3-
nitro benzaldehyde and 3-methoxyaniline to yield a brown oil.
1H NMR (300 MHz, CDCl3) d (ppm) = 8.75 (t, J = 1.9 Hz, 1H), 8.55
(s, 1H), 8.33 (ddd, J = 8.2, 2.3, 1.1 Hz, 1H), 8.25 (dt, J = 7.7, 1.2 Hz,
2H), 7.70 (t, J = 8.1 Hz, 1H), 7.33 (t, J = 7.8 Hz, 1H), 6.88–6.75 (m,
2H), 3.86 (s, 3H).
4.2.2. Saccharine acetic acid (1a)
Potassium saccharine (4.0 g, 18 mmol, 1 equiv) was mixed with
bromoacetic acid (4.52 g, 32 mmol, 1.8 equiv) and heated till the
compounds melted (ꢁ110 °C). The molten mixture was then stir-
red for 3 h. Water was added and the mixture was filtered to yield
saccharine acetic acid (1a) as a white crystalline solid (3.7 g, 85%).
1H NMR (300 MHz, DMSO) d (ppm) = 13.33 (bs, 1H), 8.38–8.33 (m,
1H), 8.20–7.86 (m, 3H), 4.49 (s, 2H).
4.2.10. (E)-1-Phenyl-N-(1H-pyrrol-2-yl)methanimine (2h)
2h was synthesized according to general procedure A from ben-
zaldehyde and 2-aminopyrrole to yield a Bordeaux reddish crys-
talline solid. 1H NMR (300 MHz, CDCl3) d (ppm) = 9.91 (bs, 1H),
8.27 (d, J = 0.6 Hz, 1H), 7.44–7.33 (m, 2H), 7.24–7.15 (m, 3H),
6.90–6.85 (m, 1H), 6.69 (dd, J = 3.6, 1.4 Hz, 1H), 6.29 (dd, J = 3.6,
2.6 Hz, 1H).
4.2.3. 6-Nitrosaccharine acetic acid (1b)
6-Nitrosaccharine (3.5 g, 11 mmol) was dissolved in DMF (6
mL). Sodium bicarbonate (1.84 g, 21.9 mmol) was added and the
mixture stirred for 30 min after which methyl bromoacetate
(1.29 mL, 13.2 mmol) was slowly added to the solution that was
then heated to 70 °C for 4 h. The mixture was poured in water
(25 mL) and the precipitate was filtered. The crude 6-nitrosaccha-
4.2.11. (E)-N-Isopropyl-1-(4-methoxyphenyl)methanimine (2k)
2k was synthesized according to general procedure A from 4-
methoxybenzaldehyde and isopropyl amine to yield a brown oil.
1H NMR (300 MHz, CDCl3) d (ppm) = 8.16 (s, 1H), 7.64–7.56 (m,
2H), 6.90–6.81 (m, 2H), 3.77 (s, 3H), 3.43 (dhept, J = 6.3, 0.6 Hz,
1H), 1.18 (d, J = 6.3 Hz, 6H).

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G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
4.2.12. (E)-N-Isopropyl-1-(p-tolyl)methanimine (2l)
4.2.17. Trans-2-(1-(4-bromophenyl)-2-(4-nitrophenyl)-4-
2l was synthesized according to general procedure A from 4-
methyl benzaldehyde and isopropyl amine to yield a pale yellow
oil. 1H NMR (300 MHz, CDCl3) d (ppm) = 8.27 (s, 1H), 7.61 (d, J =
8.1 Hz, 2H), 7.20 (d, J = 7.9, 2H), 3.61 (dhept, J = 6.3, 0.6 Hz, 1H),
2.37 (3H), 1.25 (d, J = 6.3 Hz, 6H).
oxoazetidin-3-yl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11d)
According to general procedure B, saccharinylacetic acid 1a
(50.0 mg, 0.21 mmol) was reacted with: imine 2d (63 mg, 0.21
mmol), Mukaiyama’s salt (55.6 mg, 0.22 mmol) and triethylamine
(64 lL, 0.46 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Preparative LCMS purification afforded 11d (0.05
mmol, 25%) as a white solid. 1H NMR (300 MHz, CDCl3) d (ppm)
= 8.30–8.25 (m, 2H), 8.12–8.06 (m, 1H), 7.99–7.87 (m, 3H),
7.75–7.59 (m, 2H), 7.46–7.39 (m, 2H), 7.23–7.16 (m, 2H), 5.51 (d,
J = 2.7 Hz, 1H), 5.01 (d, J = 2.7 Hz, 1H). 13C NMR (75 MHz, CDCl3)
d (ppm) = 159.10 (Cq), 158.44 (Cq), 148.99 (Cq), 137.49 (Cq),
137.15 (Cq), 135.62 (CH), 135.38 (Cq), 132.51 (2ÂCH), 131.65
(CH), 130.87 (CH), 126.44 (Cq), 125.72 (CH), 124.46 (CH), 124.46
(CH), 121.45 (CH), 121.33 (CH), 119.03 (2ÂCH), 118.15 (Cq),
63.08 (CH), 60.31 (CH). HRMS ESI (3000 V): calculated for
4.2.13. (E)-N-Isopropyl-1-(3-nitrophenyl)methanimine (2m)
2m was synthesized according to general procedure A from 2-
nitrobenzaldehyde and isopropyl amine to yield a pale yellow oil.
1H NMR (300 MHz, CDCl3) d (ppm) = 8.58–8.54 (m, 1H), 8.37 (s,
1H), 8.25 (ddd, J = 8.2, 2.3, 1.1 Hz, 1H), 8.08 (dt, J = 7.7, 1.3 Hz,
1H), 7.58 (t, J = 7.8 Hz, 1H), 3.61 (dhept, J = 6.3, 0.6 Hz, 1H), 1.28
(d, J = 6.3 Hz, 6H).
4.2.14. Trans-2-(-2-oxo-1,4-diphenylazetidin-3-yl)benzo[d]isothiazol-
3(2H)-one 1,1-dioxide (11a)
C
22H15N3O6SBr (M+H+) 527.9865, found 527.9845.
According to general procedure B, saccharinylacetic acid 1a
(50.0 mg, 0.21 mmol) was reacted with: imine 2a (37.6 mg, 0.21
mmol), Mukaiyama’s salt (55.6 mg, 0.22 mmol) and triethylamine
4.2.18. Trans-2-(1-(3-methoxyphenyl)-2-(4-methoxyphenyl)-4-
oxoazetidin-3-yl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11e)
According to general procedure B, saccharinylacetic acid 1a
(50.0 mg, 0.21 mmol) was reacted with: imine 2e (50 mg, 0.21
mmol), Mukaiyama’s salt (55.6 mg, 0.22 mmol) and triethylamine
(64 lL, 0.42 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Preparative LCMS purification afforded 11a (0.18
mmol, 86%) as a white solid. 1H NMR (300 MHz, CDCl3) d (ppm)
= 7.96–7.89 (m, 1H), 7.83–7.67 (m, 3H), 7.30–7.05 (m, 9H), 7.00–
6.90 (m, 1H), 5.33 (d, J = 2.7 Hz, 1H), 4.87 (d, J = 2.7 Hz, 1H).
13C NMR (75 MHz, CDCl3) d (ppm) = 159.76 (Cq), 158.35 (Cq),
137.57 (Cq), 136.94 (Cq), 135.32 (CH), 135.17 (Cq), 134.72 (CH),
129.44 (2ÂCH), 129.24 (CH), 129.15 (2ÂCH), 126.64 (Cq), 125.98
(2ÂCH), 125.55 (CH), 124.70 (CH), 121.25 (CH), 117.65 (2ÂCH),
63.04 (CH), 61.03 (CH). HRMS ESI (3000 V): calculated for
(64
lL, 0.46 mmol) in CH2Cl2 under microwave irradiation
(100 °C, 10 min). Preparative LCMS purification afforded 11e
(0.084 mmol, 40%) as a pale yellow solid. 1H NMR (300 MHz,
CDCl3) d (ppm) = 8.10–8.02 (m, 2H), 7.99–7.80 (m, 3H), 7.36–7.26
(m, 2H), 7.16 (t, J = 8.2 Hz, 1H), 7.05 (t, J = 2.2 Hz, 1H), 6.98–6.88
(m, 2H), 6.81 (ddd, J = 8.0, 2.0, 0.8 Hz, 1H), 6.65 (ddd, J = 8.4, 2.5,
0.8 Hz, 1H), 5.39 (d, J = 2.6 Hz), 5.39 (d, J = 2.6 Hz, 1H), 3.81 (s,
3H), 3.74 (s, 3H). 13C NMR (75 MHz, CDCl3) d (ppm) = 159.10
(Cq), 158.44 (Cq), 148.99 (Cq), 137.49 (Cq), 137.15 (Cq), 135.62
(CH), 135.38 (Cq), 132.51 (2ÂCH), 131.65 (CH), 130.87 (CH),
126.44 (Cq), 125.72 (CH), 124.46 (CH), 124.46 (CH), 121.45 (CH),
121.33 (CH), 119.03 (2ÂCH), 118.15 (Cq), 63.08 (CH), 60.31 (CH),
55.32 (CH3), 55.27 (CH3). HRMS ESI (3000 V): calculated for
C
22H13N2O4S (M+H+) 405.0909, found 405.0911.
4.2.15. Trans-2-(1-(4-bromophenyl)-2-(4-methoxyphenyl)-4-
oxoazetidin-3-yl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11b)
According to general procedure B, saccharinylacetic acid 1a
(50.0 mg, 0.21 mmol) was reacted with: imine 2b (60.2 mg, 0.21
mmol), Mukaiyama’s salt (55.6 mg, 0.22 mmol) and triethylamine
C
22H15N3O6SBr (M+H+) 527.9865, found 527.9845. HRMS ESI
(64
lL, 0.42 mmol) in CH2Cl2 under microwave irradiation (100
(3000 V): calculated for C24H21N2O6S (M+H+) 465.1120, found
465.1166.
°C, 10 min). Preparative LCMS purification afforded 11b (0.09
mmol, 42%) as a white solid. 1H NMR (300 MHz, CDCl3) d (ppm)
= 8.10–8.04 (m, 1H), 7.98–7.83 (m, 3H), 7.43–7.34 (m, 2H), 7.33–
7.19 (m, 4H), 6.97–6.88 (m, 2H), 5.38 (d, J = 2.6 Hz, 1H), 4.98 (d,
J = 2.6 Hz, 1H), 3.82 (s, 3H). 13C NMR (75 MHz, CDCl3) d (ppm) =
160.42 (Cq), 159.89 (Cq), 158.37 (Cq), 137.61 (Cq), 135.98 (Cq),
135.35 (CH), 134.74 (CH), 132.17 (2ÂCH), 127.34 (2ÂCH), 126.64
(Cq), 126.50 (Cq), 125.57 (CH), 121.28 (CH), 119.22 (2ÂCH),
117.51 (Cq), 114.97 (2ÂCH), 62.41 (CH), 60.96 (CH), 55.35 (CH3).
4.2.19. Trans-2-(1-(3-methoxyphenyl)-2-oxo-4-(p-tolyl)azetidin-3-yl)
benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11f)
According to general procedure B, saccharinylacetic acid 1a
(50.0 mg, 0.21 mmol) was reacted with: imine 2f (47 mg, 0.21
mmol), Mukaiyama’s salt (55.6 mg, 0.22 mmol) and triethylamine
(64 lL, 0.46 mmol) in CH2Cl2 under microwave irradiation
(100 °C, 10 min). Preparative LCMS purification afforded 11f
(0.84 mmol, 40%) as a pale yellow solid. 1H NMR (300 MHz, CDCl3)
d (ppm) = 8.10–8.02 (m, 2H), 7.97–7.81 (m, 3H), 7.32–7.10 (m, 5H),
7.07 (t, J = 2.2 Hz, 1H), 6.80 (ddd, J = 8.0, 1.9, 0.8 Hz, 1H), 6.65 (ddd,
J = 8.3, 2.5, 0.8 Hz, 1H), 5.40 (d, J = 2.6 Hz), 1H), 4.98 (d, J = 2.7 Hz,
1H), 3.75 (s, 3H), 2.36 (s, 3H). 13C NMR (75 MHz, CDCl3) d (ppm)
= 160.12 (Cq), 159.93 (Cq), 158.33 (Cq), 139.16 (Cq), 138.09 (Cq),
137.61 (Cq), 135.28 (CH), 134.68 (CH), 132.15 (CH), 130.10
(2ÂCH), 129.90 (CH), 126.67 (Cq), 125.90 (2ÂCH), 125.53 (CH),
121.23 (CH), 110.67 (CH), 109.81 (CH), 103.62 (CH), 63.12 (CH),
61.13 (CH), 55.27 (CH3), 21.22 (CH3). HRMS ESI (3000 V): calcu-
lated for C24H21N2O5S (M+H+) 449.1171, found 465.1165.
HRMS ESI (3000 V): calculated for
513.0120, found 513.0114.
C
23H19N2O5SBr (M+H+)
4.2.16. Trans-2-(2-(4-methoxyphenyl)-4-oxo-1-(p-tolyl)azetidin-3-yl)
benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11c)
According to general procedure B, saccharinylacetic acid 1a
(25.0 mg, 0.10 mmol) was reacted with: imine 2c (28.4 mg, 0.10
mmol), Mukaiyama’s salt (27.8 mg, 0.11 mmol) and triethylamine
(32
lL, 0.23 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Preparative LCMS purification afforded 11c (0.05
mmol, 50%) as a white solid. 1H NMR (300 MHz, CDCl3) d (ppm)
= 8.10–8.03 (m, 2H), 7.98–7.83 (m, 3H), 7.43–7.34 (m, 2H), 7.28–
7.17, (m, 6H), 5.39 (d J = 2.7 Hz 1H), 4.99 (d, J = 2.7 Hz, 1H), 2.37
(s, 3H). 13C NMR (75 MHz, CDCl3) d (ppm) = 159.85 (Cq), 158.37
(Cq), 139.45 (Cq), 137.62 (Cq), 135.99 (Cq), 135.35 (CH), 134.74
(CH), 132.17 (2ÂCH), 130.22 (2ÂCH), 126.63 (Cq), 125.89 (2ÂCH),
125.57 (CH), 121.28 (CH), 119.20 (2ÂCH), 117.50 (Cq), 63.34
(CH), 61.14 (CH), 21.24 (CH3). HRMS ESI (3000 V): calculated for
4.2.20. Trans-2-(1-(3-methoxyphenyl)-2-(4-nitrophenyl)-4-
oxoazetidin-3-yl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11g)
According to general procedure B, saccharinylacetic acid 1a
(25.0 mg, 0.10 mmol) was reacted with: imine 2g (26.6 mg, 0.10
mmol), Mukaiyama’s salt (27.8 mg, 0.11 mmol) and triethylamine
(32
lL, 0.23 mmol) in CH2Cl2 under microwave irradiation
C
23H18N2O4SBr (M+H+) 497.0171, found 497.0168.
(100 °C, 10 min). Preparative LCMS purification afforded 11g

G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
47
(0.03 mmol, 30%) as a pale yellow solid. 1H NMR (300 MHz, CDCl3)
4.2.24. Trans-2-(1-isopropyl-2-(4-nitrophenyl)-4-oxoazetidin-3-yl)
d (ppm) = 8.32–8.25 (m, 2H), 8.13–8.06 (m, 1H), 8.00–7.85 (m, 3H),
7.73 (dt, J = 7.7, 1.2 Hz, 1H), 7.62 (dt, J = 7.8, 0.5 Hz, 1H), 7.19
(t, J = 8.2 Hz, 1H), 7.03 (t, J = 2.2 Hz, 1H), 6.75–6.66 (m, 2H), 5.52
(d, J = 2.6 Hz, 1H), 4.99 (d, J = 2.7 Hz, 1H), 3.77 (s, 3H). 13C NMR
(75 MHz, CDCl3) d (ppm) = 160.35 (Cq), 159.14 (Cq), 158.39 (Cq),
148.93 (Cq), 137.61 (Cq), 137.50 (Cq), 137.47 (Cq), 135.54 (CH),
134.89 (CH), 131.75 (CH), 130.72 (CH), 130.22 (CH), 126.51 (Cq),
125.68 (CH), 124.28 (CH), 121.41 (CH), 121.31 (CH), 110.97 (CH),
109.53 (CH), 103.79 (CH), 62.84 (CH), 60.31 (CH), 55.37 (CH3).
benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11m)
According to general procedure B, saccharinylacetic acid 1a
(25.0 mg, 0.10 mmol) was reacted with: imine 2m (19.9 mg, 0.10
mmol), Mukaiyama’s salt (27.8 mg, 0.11 mmol) and triethylamine
(32 lL, 0.23 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Preparative LCMS purification afforded 11m (0.051
mmol, 51%) as a white solid. 1H NMR (300 MHz, CDCl3) d (ppm)
= 8.12–8.06 (m, 1H), 7.97–7.84 (m, 3H), 7.77 (dt, J = 7.8, 1.3 Hz,
1H), 7.65 (dt, J = 7.9, 0.3 Hz, 1H), 5.12 (d, J = 2.4 Hz, 1H), 4.81 (d,
J = 2.4 Hz, 1H), 3.89 (sept, J = 6.8 Hz, 1H), 1.44 (d, J = 6.8 Hz, 3H),
1.17 (d J = 6.8 Hz, 3H). 13C NMR (75 MHz, CDCl3) d (ppm) =
162.40 (Cq), 158.49 (Cq), 148.78 (Cq), 139.39 (Cq), 137.52 (Cq),
135.37 (CH), 134.78 (CH), 132.23 (CH), 130.46 (CH), 126.64 (Cq),
125.53 (CH), 124.17 (CH), 121.62 (CH), 121.31 (CH), 62.42 (CH),
58.52 (CH), 46.44 (CH), 20.84 (CH3), 20.18 (CH3). HRMS ESI
(3000 V): calculated for C19H18N3O6S (M+H+) 416.0916, found
416.0932.
HRMS ESI (3000 V): calculated for
480.0865, found 480.0868.
C
23H18N3O7SBr (M+H+)
4.2.21. Trans-2-(2-oxo-1-phenyl-4-(1H-pyrrol-2-yl)azetidin-3-yl)
benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11h)
According to general procedure B, saccharinylacetic acid 1a
(25.0 mg, 0.10 mmol) was reacted with: imine 2h (17.6 mg, 0.10
mmol), Mukaiyama’s salt (27.8 mg, 0.11 mmol) and triethylamine
(32 lL, 0.23 mmol) in CH2Cl2 under microwave irradiation
4.2.25. tert-Butyl trans-3-(3-(1,1-dioxido-3-oxobenzo[d]isothiazol-2
(3H)-yl)-2-oxo-4-(p-tolyl)azetidin-1-yl)propanoate (11o)
According to general procedure B, saccharinylacetic acid 1a
(50.0 mg, 0.21 mmol) was reacted with: imine 2o (53.8 mg, 0.22
mmol), Mukaiyama’s salt (55.6 mg, 0.22 mmol) and triethylamine
(100 °C, 10 min). Preparative LCMS purification afforded 11h
(0.035 mmol, 35%) as a pale yellow solid. 1H NMR (300 MHz,
CDCl3) d (ppm) = 8.11–8.04 (m, 1H), 8.01–7.80 (m, 3H), 7.24–7.10
(m, 3H), 6.86–6.68 (m, 3H), 6.56 (t, J = 3.2 Hz, 1H), 6.29–6.25
(m, 1H), 5.54–4.49 (m, 1H), 5.09 (d, J = 5.4 Hz, 1H). 13C NMR
(75 MHz, CDCl3) d (ppm) = 163.11, (Cq), 158.82 (Cq), 145.50 (Cq),
137.70 (Cq), 129.47 (2ÂCH), 125.67 (CH), 121.39 (CH), 119.60
(CH), 119.54 (CH), 114.39 (2ÂCH), 113.00 (CH), 107.42 (CH),
60.86 (CH), 52.56 (CH). HRMS ESI (3000 V): calculated for
(64 lL, 0.46 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Preparative LCMS purification afforded 11o (0.015
mmol, 8%) as a colorless oil. 1H NMR (300 MHz, CDCl3) d (ppm) =
8.14–8.01 (m, 1H), 7.98–7.80 (m, 3H), 7.24 (s, 4H), 5.02 (d, J =
2.4 Hz, 1H) 4.85 (d, J = 2.4 Hz, 1H), 3.82 (ddd, J = 13.9, 7.6, 5.9 Hz,
1H), 3.30–3.16 (m, 1H), 2.78–2.51 (m, 2H), 2.38 (s, 3H), 1.43 (s,
9H). 13C NMR (75 MHz, CDCl3) d (ppm) = 170.21 (Cq), 162.91
(Cq), 158.34 (Cq), 139.21 (Cq), 137.62 (Cq), 135.14 (CH), 134.59
(CH), 132.19 (Cq), 129.99 (2ÂCH), 126.82 (Cq), 126.35 (2ÂCH),
125.40 (CH), 121.19 (CH), 81.09 (Cq), 63.10 (CH), 61.01 (CH),
37.04 (CH2), 33.31 (CH2), 28.01 (3ÂCH3), 21.24 (CH3). HRMS ESI
(3000 V): calculated for C24H26N2O6SNa (M+Na+) 493.1409, found
493.1429.
C
20H16N3O4S (M+H+) 394.0862, found 394.0861.
4.2.22. Trans-2-(1-isopropyl-2-(4-methoxyphenyl)-4-oxoazetidin-3-
yl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide (11k)
According to general procedure B, saccharinylacetic acid 1a
(25.0 mg, 0.10 mmol) was reacted with: imine 2k (18.4 mg, 0.10
mmol), Mukaiyama’s salt (27.8 mg, 0.11 mmol) and triethylamine
(32 lL, 0.23 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Preparative LCMS purification afforded 11k (0.063
mmol, 63%) as a white solid. 1H NMR (300 MHz, CDCl3) d (ppm)
= 8.10–8.04 (m, 1H), 7.95–7.81 (m, 3H), 7.35–7.28 (m, 2H), 6.99–
6.90 (m, 2H), 4.98 (d, J = 2.4 Hz, 1H), 4.82 (d, J = 2.4 Hz, 1H),
3.92–3.75 M, 1H), 3.83 (s, 3H), 1.40 (d, J = 6.8 Hz, 3H), 1.13 (d, J =
6.7 Hz, 3H). 13C NMR (75 MHz, CDCl3) d (ppm) = 162.74 (Cq),
160.22 (Cq), 158.46 (Cq), 137.61 (Cq), 135.11 (CH), 134.58 (CH),
128.51 (Cq), 127.86 (2ÂCH), 125.37 (CH), 121.16 (CH), 114.55
(2ÂCH), 62.42 (CH), 58.96 (CH), 55.34 (CH3), 45.87 (CH), 20.80
(CH3), 20.08 (CH3). HRMS ESI (3000 V): calculated for C20H21N2O5-
SNa (M+Na+) 423.1002, found 423.0991.
4.2.26. Trans-2-(1-(4-bromophenyl)-2-oxo-4-(p-tolyl)azetidin-3-yl)-
6-nitrobenzo[d]isothiazol-3(2H)-one 1,1-dioxide (11p)
According to general procedure B, 6-nitroaccharinylacetic acid
2b (71.55 mg, 0.25 mmol) was reacted with: imine 2c (68.5 mg,
0.25 mmol), Mukaiyama’s salt (70.3 mg, 0.27 mmol) and triethy-
lamine (77 lL, 0.55 mmol) in CH2Cl2 under microwave irradiation
(100 °C, 10 min). Column chromatography (heptane:EtOAc/99:1
? 1:1) afforded 11p (0.15 mmol, 61%) as a white solid. 1H NMR
(300 MHz, d6-DMSO) d (ppm) = 8.78 (dd, J = 1.9, 0.5 Hz, 1H), 8.70
(dd, J = 8.4, 1.9 Hz, 1H), 8.27 (dd, J = 8.3, 0.5 Hz, 1H), 7.44 (m, 2H),
7.28–7.16 (m, 6H), 5.39 (d, J = 2.6 Hz, 1H), 5.01 (d, J = 2.6 Hz, 1H),
2.38 (s, 3H). 13C NMR (75 MHz, d6-DMSO) d (ppm) = 158.96 (Cq),
156.35 (Cq), 151.81 (Cq), 139.74 (Cq), 138.79 (Cq), 135.75 (Cq),
132.25 (2ÂCH), 131.21 (Cq), 130.88 (Cq), 130.33 (2ÂCH), 129.74
(CH), 127.20 (CH), 125.86 (2ÂCH), 119.19 (2ÂCH), 117.77 (Cq),
117.37 (CH), 63.52 (CH), 60.31 (CH), 21.26 (CH3). HRMS ESI
(3000 V): calculated for C23H17N3O6SBr (M+H+) 542.0021, found
542.0007.
4.2.23. Trans-2-(1-isopropyl-2-oxo-4-(p-tolyl)azetidin-3-yl)benzo[d]
isothiazol-3(2H)-one 1,1-dioxide (11l)
According to general procedure B, saccharinylacetic acid 1a
(25.0 mg, 0.10 mmol) was reacted with: imine 2 l (16.7 mg, 0.10
mmol), Mukaiyama’s salt (27.8 mg, 0.11 mmol) and triethylamine
(32 lL, 0.23 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Preparative LCMS purification afforded 11l (0.032
mmol, 32%) as a white solid. 1H NMR (300 MHz, CDCl3) d (ppm)
= 8.10–8.03 (m, 1H), 7.94–7.80 (m, 3H), 7.34–7.18 (m, 4H), 5.00
(d, J = 2.4 Hz, 1H), 4.83 (d, J = 2.4 Hz, 1H), 3.83 (sept, J = 6.8 Hz,
1H), 2.37 (s, 3H), 1.41 (d, J = 6.8 Hz, 3H), 1.14 (d, J = 6.7 Hz, 3H).
13C NMR (75 MHz, CDCl3) d (ppm) = 162.95 (Cq), 158.46 (Cq),
139.11 (Cq), 137.59 (Cq), 135.12 (CH), 134.58 (CH), 133.53 (Cq),
129.84 (2ÂCH), 126.81 (Cq), 126.48 (2ÂCH), 125.37 (CH), 121.15
(CH), 62.30 (CH), 59.26 (CH), 46.01 (CH3), 21.22 (CH), 20.77
(CH3), 20.06 (CH3). HRMS ESI (3000 V): calculated for C20H21N2O4S
(M+H+) 385.1213, found 385.1222.
4.2.27. Trans-2-(1-(4-bromophenyl)-2-(4-methoxyphenyl)-4-
oxoazetidin-3-yl)-6-nitrobenzo[d]isothiazol-3(2H)-one 1,1-dioxide
(11q)
According to general procedure B, 6-nitrosaccharinylacetic acid
1b (400 mg, 1.4 mmol) was reacted with: imine 2b (405 mg, 1.4
mmol), Mukaiyama’s salt (375 mg, 1.5 mmol) and triethylamine
(0.43 mL, 3.1 mmol) in CH2Cl2 (10 mL) under microwave irradia-
tion (100 °C, 10 min). Column chromatography (heptane:
EtOAc/4:1 ? 2:1) afforded 11q (0.854 mmol, 61%) as a pale yellow

48
G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
solid. 1H NMR (300 MHz, d6-DMSO) d (ppm) = 9.37 (d, J = 1.9 Hz,
1H), 8.76 (dd, J = 8.4, 2.0 Hz, 1H), 8.35 (d, J = 8.4 Hz, 1H), 7.60–
7.42 (m, 4H), 7.24–7.14 (m, 2H), 7.02–6.91 (m, 2H), 5.61 (d, J =
2.7 Hz, 1H), 5.39 (d, J = 2.7 Hz, 1H), 3.76 (s, 3H). 13C NMR (75
MHz, CDCl3) d (ppm) = 160.68 (Cq), 160.19 (Cq), 157.30 (Cq),
152.47 (Cq), 138.02 (Cq), 136.35 (Cq), 132.70 (2ÂCH), 131.07
(Cq), 131.05 (CH), 129.03 (2ÂCH), 127.49 (CH), 127.07 (Cq),
119.67 (2ÂCH), 119.04 (CH), 116.81 (Cq), 114.81 (2ÂCH), 62.61
(CH), 60.07 (CH), 55.64 (CH3). HRMS ESI (3000 V): calculated for
4.2.31. Trans-N-(2-(1-(4-bromophenyl)-2-(4-methoxyphenyl)-4-
oxoazetidin-3-yl)-1,1-dioxido-3-oxo-2,3-dihydrobenzo[d]isothiazol-
6-yl)acetamide (23b)
Lactam 11q (200 mg, 0.36 mmol) was dissolved in glacial acetic
acid (3 mL) followed by the addition of powdered iron (200 mg,
3.6 mmol). The mixture was stirred for 1 h after which the reaction
was complete (TLC). The mixture was filtered over Celite, diluted in
EtOAc and washed with saturated NaHCO3 till no more CO2
evolved. The organic layer was then washed with brine, dried over
Na2SO4 and concentrated in vacuo. This afforded 23b (0.35 mmol,
99%) as a yellow solid. 1H NMR (300 MHz, CDCl3) d (ppm) = 7.44–
7.04 (m, 7H), 6.89–6.60 (m 4H), 5.32 (d, J = 1.6 Hz, 1H), 5.02 (bs,
2H), 4.83 (d, J = 1.9 Hz, 1H), 3.70 (s, 3H). 13C NMR (75 MHz, CDCl3)
d (ppm) = 161.57 (Cq), 160.26 (Cq), 158.75 (Cq), 153.86 (Cq),
139.52 (Cq), 135.72 (Cq), 132.11 (2ÂCH), 127.28 (2ÂCH), 126.78
(CH), 119.21 (2ÂCH), 118.88 (CH), 117.55 (Cq), 114.83 (2ÂCH),
113.37 (Cq), 104.82 (CH), 62.97 (CH), 60.97 (CH), 55.27 (CH3).
C
23H17N3O7SBr (M+H+) 557.9971, found 557.9968.
4.2.28. Trans-2-(1-(4-bromophenyl)-2-oxo-4-(p-tolyl)azetidin-3-yl)
isoindoline-1,3-dione (18)
According to general procedure B, phthaloyl glycine 13 (51.3
mg, 0.25 mmol) was reacted with: imine 2b (68.5 mg, 0.25 mmol),
Mukaiyama’s salt (70.3 mg, 0.27 mmol) and triethylamine (77 lL,
0.55 mmol) in CH2Cl2 under microwave irradiation (100 °C, 10
min). Column chromatography (heptane:EtOAc/99:1 ? 1:1)
afforded 18 (0.15 mmol, 58%) as a white solid. 1H NMR (300
MHz, CDCl3) d (ppm) = 7.93–7.84 (m, 2H), 7.82–7.73 (m, 2H),
7.43–7.34 (m, 2H), 7.28–7.17 (m, 6H), 5.32 (d, J = 2.7 Hz, 1H),
5.27 (d, J = 2.7 Hz, 1H), 2.36 (s, 3H). 13C NMR (75 MHz, CDCl3)
d (ppm) = 166.74 (Cq), 162.09 (Cq), 139.32 (Cq), 136.14 (Cq),
134.61 (2ÂCH), 132.23 (Cq), 132.11 (2ÂCH), 131.64 (Cq), 130.16
(2ÂCH), 126.05 (2ÂCH), 123.84 (2ÂCH), 119.12 (2ÂCH), 119.12
(2ÂCH), 117.24 Cq), 62.97 (CH), 61.28 (CH), 21.23 (CH3). HRMS
ESI (3000 V): calculated for C24H18N2O3Br (M+H+) 461.0501, found
461.0486.
HRMS ESI (3000 V): calculated for
528.0229, found 528.0221.
C
23H19N3O5SBr (M+H+)
4.2.32. Trans-N-(2-(1-(4-bromophenyl)-2-oxo-4-(p-tolyl)azetidin-3-
yl)-1,1-dioxido-3-oxo-2,3-dihydrobenzo[d]isothiazol-6-yl)acetamide
(24a)
Lactam 23a (21 mg, 0.04 mmol) and sodium bicarbonate (8.6
mg, 0.10 mmol) were dissolved in THF (1.0 mL). Then acetyl chlo-
ride (3.5 lL, 0.05 mmol) was added and the mixture was stirred
for 16 h after which the reaction was complete (TLC). The volatiles
were evaporated and suspended in EtOAc (2 mL). The organic layer
was washed with 1 M HCl, brine, dried over Na2SO4 and evapo-
rated. Column chromatography (heptane:EtOAc/99:1 ? 25:75)
afforded 24a (0.027 mmol, 66%) as a white solid. 1H NMR (300
MHz, CDCl3) d (ppm) = 9.03 (s, 1H), 8.70 (d, J = 1.7 Hz, 1H), 7.60–
7.31 (m, 4H), 7.30–7.16 (m, 6H), 5.54 (d, J = 2.7 Hz, 1H), 5.00 (d, J
= 2.7 Hz, 1H), 2.36 (s, 3H), 2.21 (s, 3H). 13C NMR (75 MHz, CDCl3)
d (ppm) = 169.46 (Cq), 162.18 (Cq), 157.86 (Cq), 145.47 (Cq),
139.74 (Cq), 138.48 (Cq), 135.38 (Cq), 132.36 (2ÂCH), 131.00
(Cq), 125.92 (CH), 125.85 (2ÂCH), 123.68 (CH), 119.50 (2ÂCH),
118.27 (Cq), 111.24 (CH), 62.78 (CH), 60.82 (CH), 24.63 (CH3),
21.24 (CH3). HRMS ESI (3000 V): calculated for C25H21N3O5SBr (M
+H+) 554.0380, found 554.0362.
4.2.29. 1,3-Dimethyl-7-trans-(1-(3-nitrophenyl)-2-oxo-4-(p-tolyl)
azetidin-3-yl)-3,7-dihydro-1H-purine-2,6-dione (19)
According to general procedure B, theophylline-7-acetic acid 14
(29.8 mg, 0.125 mmol) was reacted with: imine 2b (34.3 mg, 0.12
mmol), Mukaiyama’s salt (35.1 mg, 0.14 mmol) and triethylamine
(39 lL, 0.28 mmol) in CH2Cl2 under microwave irradiation (100
°C, 10 min). Column chromatography (heptane:EtOAc/4:1 ?
0:100) afforded 19 (0.078 mmol, 65%) as a white solid. 1H NMR
(300 MHz, CDCl3) d (ppm) = 7.66 (s, 1H), 7.45–7.37 (m, 2H), 7.32–
7.20 (m, 6H), 5.48 (d, J = 2.7 Hz, 1H), 5.31 (d, J = 2.7 Hz, 1H), 3.62
(s, 3H), 3.36 (s, 3H), 2.39 (s, 3H). 13C NMR (75 MHz, CDCl3)
d (ppm) = 160.49 (Cq), 154.61 (Cq), 151.45 (Cq), 149.56 (Cq),
141.3 (CH, not observed in APT; determined from HSQC spectrum),
139.78 (Cq), 132.25 (2ÂCH), 131.33 (Cq), 130.26 (2ÂCH), 126.21
(2ÂCH) 119.44 (2ÂCH), 117.80 (Cq), 70.12 (CH), 64.32 (CH),
29.93 (CH3), 28.29 (CH3), 21.26 (CH3). HRMS ESI (3000 V): calcu-
lated for C23H21N5O3Br (M+H+) 494.0828, found 494.0838.
4.2.33. Trans-N-(2-(1-(4-bromophenyl)-2-(4-methoxyphenyl)-4-
oxoazetidin-3-yl)-1,1-dioxido-3-oxo-2,3-dihydrobenzo[d]isothiazol-
6-yl)acetamide (24b)
Lactam 23b (66.1 mg, 0.13 mmol) and sodium bicarbonate
(26.2 mg, 0.31 mmol) were dissolved in THF (1.5 mL). Then acetyl
chloride (11 lL, 0.15 mmol) was added and the mixture was stir-
4.2.30. Trans-6-amino-2-(1-(4-bromophenyl)-2-oxo-4-(p-tolyl)
azetidin-3-yl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide (23a)
Lactam 11p (50 mg, 0.090 mmol) was dissolved in glacial acetic
acid (1 mL) followed by the addition of powdered iron (0.51 mg,
0.92 mmol). The mixture was stirred for 3 h after which the reac-
tion was complete (TLC). The mixture was filtered over Celite,
diluted in EtOAc and washed with saturated NaHCO3 till no more
CO2 evolved. The organic layer was then washed with brine, dried
over Na2SO4 and concentrated in vacuo. This afforded 23a (0.85
mmol, 92%) as an off-white solid. 1H NMR (300 MHz, CDCl3)
d (ppm) = 7.44 (d, J = 8.4 Hz, 1H), 7.32–7.23 (m, 2H), 7.17–7.05
(m, 6H), 6.79–6.70 (m, 2H), 5.29 (d, J = 2.6 Hz, 1H), 4.84 (bs, 2H),
4.80 (d J = 2.7 Hz, 1H), 2.25 (s, 3H). 13C NMR (75 MHz, CDCl3)
d (ppm) = 161.35 (Cq), 158.73 (Cq), 153.61 (Cq), 139.56 (Cq),
139.35 (Cq), 135.89 (Cq), 132.17 (2ÂCH), 131.66 (Cq), 130.17
(Cq), 126.96 (CH), 125.86 (2ÂCH), 119.24 (2ÂCH), 119.00 (CH),
117.56 (Cq), 114.00 (Cq), 104.92 (CH), 63.06 (CH), 31.22 (CH),
21.23 (CH3). HRMS ESI (3000 V): calculated for C23H19N3O4SBr (M
+H+) 512.280, found 512.0294.
red for 3 h after which the reaction was complete (TLC). The vola-
tiles were evaporated and suspended in EtOAc (5 mL). The organic
layer was washed with 1 M HCl, brine, dried over Na2SO4 and evap-
orated. This yielded 24b (0.12 mmol, 95%) as a white solid. 1H NMR
(300 MHz, CDCl3) d (ppm) = 9.04 (s, 1H), 8.71 (d, J = 1.7 Hz, 1H),
7.53–7.40 (m, 3H), 7.39–7.20 (m, 5H), 6.98–6.88 (m, 2H), 5.53
(d, J = 2.6 Hz, 1H), 5.00 (d, J = 2.7 Hz, 1H), 3.81 (s, 3H), 2.22 (s,
3H). 13C NMR (75 MHz, CDCl3) d (ppm) = 169.51 (Cq), 162.28
(Cq), 160.60 (Cq), 157.89 (Cq), 145.50 (Cq), 138.49 (Cq), 138.49
(Cq), 135.38 (Cq), 132.40 2ÂCH), 127.37 (2ÂCH), 125.95 (CH),
125.81 (Cq), 123.71 (CH), 119.56 (2ÂCH), 118.33 (Cq), 115.10
(2ÂCH), 111.28 (CH), 62.86 (CH), 60.68 (CH), 55.42 (CH3), 24.69
(CH3). HRMS ESI (3000 V): calculated for C25H22N3O6SBr (M+H+)
570.0334, found 570.0318.
Author contributions
All authors have approved the final version of the manuscript.

G.V. Janssen et al. / Bioorganic & Medicinal Chemistry 26 (2018) 41–49
49
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Conflicts of interest
None.
Acknowledgments
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The research leading to these results was performed within the
European Lead Factory and has received support from the Innova-
tive Medicines Initiative Joint Undertaking under grant agreement
no. 115489, resources of which are composed of financial contribu-
tion from the European Union’s Seventh Framework Programme
(FP7/2007-2013) and EFPIA companies’ in-kind contribution.
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19. The stereochemistry of the lactam rings were assigned by comparing the
coupling constants of H-3 and H-4 (J3,4 > 4.0 Hz) for the cis stereoisomer and
(J3,4 < 3.0 Hz) for the trans stereoisomer.
20. The yields are determined from the pure products after preparative HPLC (see
Experimental section for details). Since a part of the product is lost during these
purifications, the yields are lower than the products that are isolated by FC-
chromatography.
A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at https://doi.org/10.1016/j.bmc.2017.11.014.
References
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23. For practical reasons, conventional heating in closed vials at 45 °C was applied
for 16 h instead of microwave heating.