Asymmetric synthesis of photophore-containing lactisole derivatives to elucidate sweet taste receptors

Article abstract of DOI:10.3390/molecules25122790

Lactisole, which has a 2-phenoxy propionic acid skeleton, is well-known as an inhibitor of sweet taste receptors. We recently revealed some of the structure-activity relationships of the aromatic ring and chiral center of lactisole. Photoaffinity labeling

Full text of DOI:10.3390/molecules25122790

molecules
Article
Asymmetric Synthesis of Photophore-Containing
Lactisole Derivatives to Elucidate Sweet
Taste Receptors
Tomoya Nakagita 1,2,† , Akiko Ishida 3,†, Zetryana Puteri Tachrim 3,4, Lei Wang 3,5
,
Takumi Misaka 1 and Makoto Hashimoto 3,
*
1
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences,
The University of Tokyo, Tokyo 113-8657, Japan; nakagita.tomoya.eo@ehime-u.ac.jp (T.N.);
amisaka@mail.ecc.u-tokyo.ac.jp (T.M.)
Proteo-Science Center, Ehime University, Ehime 791-8577, Japan
Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9,
Kita-ku, Sapporo 060-8589, Japan; a-ishida@frontier.hokudai.ac.jp (A.I.); zetry@chem.itb.ac.id (Z.P.T.);
leiwang@dlut.edu.cn (L.W.)
Program Study of Chemistry, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung,
Jalan Ganesha 10, Bandung 40132, Indonesia
Department of Pharmacy, School of Chemical Engineering, Dalian University of Technology,
Dalian 116023, China
2
3
4
5
*
†
Correspondence: hasimoto@abs.agr.hokudai.ac.jp; Tel.: +81-11-7063849
These authors contributed equally to this work.
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 29 May 2020; Accepted: 16 June 2020; Published: 17 June 2020
Abstract: Lactisole, which has a 2-phenoxy propionic acid skeleton, is well-known as an inhibitor of
sweet taste receptors. We recently revealed some of the structure–activity relationships of the aromatic
ring and chiral center of lactisole. Photoaffinity labeling is one of the common chemical biology
methods to elucidate the interaction between bioactive compounds and biomolecules. In this paper,
the novel asymmetric synthesis of lactisole derivatives with common photophores (benzophenone,
azide and trifluoromethyldiazirine) for photoaffinity labeling is described. The synthetic compounds
are subjected to cell-based sweet taste receptors, and the substitution with trifluoromethyldiazirinyl
photophore shows the highest affinity to the receptor of the synthesized compounds.
Keywords: lactisole; photoaffinity label; sweet taste; diazirine; azide; benzophenone
1. Introduction
Lactisole (2-(4-methoxyphenoxy)propanoic acid) [
receptors and has been shown to interactwiththetransmembranedomainoftheT1R3subunit(T1R3-TMD)
of the receptor [ ]. The mother skeleton, 2-phenoxypropanoic acid, is found in several phenoxy herbicides,
such as 2-(2,4-dichlorophenoxy)propanoic acid (dichlorprop, 2,4-DP) 2-(4-chlorophenoxy)propanoic
acid (4-CPP) [ ], and (R)-isomers of them have herbicide activities. We recently reported that the
(S)-isomers at the 2-position of lactisole and 2,4-DP at the 2-position have higher affinity for sweet
taste receptor than (R)-isomers [ ]. These results are inconsistent with the herbicide activity for
2-phenoxypropanoic acid [ ]. The detailed functional analysis of the stereocenter may be important to
elucidate sweet taste receptors.
Photoaffinity labeling [
1,2] is well-known as an inhibitor of sweet taste
3
4
5
6
7–10] is a useful biochemical method for the analysis of biological
interactions between low-molecular-weight bioactive compounds and biomolecules. The methodology
may afford other information near the binding sites which cannot be obtained from
Molecules 2020, 25, 2790; doi:10.3390/molecules25122790
www.mdpi.com/journal/molecules

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structure–activity relationship studies. Three major photophores—phenylazide, benzophenone
and (trifluoromethyl)phenyldiazirine—are used for photoaffinity labeling [11]. We reported several
preparations of gustatory ligands to elucidate gustatory receptors [12–20]; however, there are few
studies on the synthesis of photoreactive lactisole derivatives which have aimed to elucidate their
biological activities. In this paper, we describe the comprehensive synthesis of photoreactive lactisole
derivatives (Figure 1), which we then used in an inhibitory activity assay for cell-based human sweet
taste receptors.
Figure 1. Structures of photoreactive lactisole derivatives in this study.
2. Results
2.1. Synthesis
The key steps to construct a lactisole skeleton in an asymmetric manner are achieved by the
Mitsunobu reaction for optically pure methyl lactate and phenol derivatives of photophore precursors.
Details for each photophore are described below.
2.1.1. Benzophenone-Based Lactisole Derivatives
A few reports have described the preparations of racemic benzophenone-based lactisole derivatives
and their separation by chromatography [21–25]. However, to date, the asymmetric synthesis
of benzophenone-modified lactisole derivatives has not been reported. Hydroxybenzophenone
derivatives (1–3), optically pure methyl lactate (4 and 5, 1.5 equiv.) and triphenylphosphine (1.2 equiv.)
were preincubated at 0 ◦C for 10 min in dichloromethane and diethyl azodicarboxylate (1.5 equiv.) was
slowly added to the solution. The reaction mixture was stirred at room temperature overnight and
worked up with a general procedure. Purification with column chromatography afforded the optically
pure methyl 2-benzoylphenoxypropionate derivatives
subjected to chiral high-performance liquid chromatography (HPLC) with Chiralpak IG [
6
–
8
with a good yield. The methyl esters were
] to ensure
2
the configuration of the chiral center. The methyl esters were hydrolyzed under reflux in the presence
of K2CO3 to afford derivatives 9–13 in high yields (Figure 2).
◦
a) (1) PPh3, CH2Cl2, 0 C,
Figure 2. Synthesis of benzophenone-containing lactisole derivatives. (
10 min; (2) diethyl azodicarboxylate (DEAD), CH2Cl2, rt, 8 h, (S)- 88%, (R)-
(R)-7 quant, (S)- 88%, (R)- 82%; ( ) K2CO3, CH3OH, H2O, reflux, 2 h, (S)-
6
6
9
quant., (S)- quant.,
quant, (R)-9 quant.,
7
8
8
b
(S)-10 80%, (R)-10 quant, (S)-11 87%, (R)-11 88%.
2.1.2. Azide-Based Lactisole Derivatives
An example of the synthesis of racemic azide-based lactisole ethyl ester has been reported
previously [26], but to date, the asymmetric synthesis of azide modified on the aromatic ring of
the lactisole skeleton has not been reported. Akazome et al. reported the asymmetric synthesis of
(R)-2-nitro (R)-23 [27] and (R)-3-nitro (R)-15 [28,29]-substituted lactisole methyl ester. Our retrosynthesis

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for comprehensive preparations of azide-based lactisole derivatives was based on the asymmetric
synthesis of nitro-substituted lactisole skeletons, followed by the conversion of the nitro group to azide
derivatives. First, 4- and 3- Nitrophenol 12 and 13, and optically pure methyl lactate 4 and 5 (1.5 equiv.)
and triphenylphosphine (1.2 equiv.) were preincubated at 0 ◦C for 10 min in dichloromethane. Diethyl
azodicarboxylate (1.5 equiv.) was slowly added to the solution to construct nitro-substituted methyl
lactisole 14 and 15. Nitro groups were reduced under a hydrogen atmosphere in the presence of 5%
Pd/C to afford amino derivatives 16 and 17. The aniline derivatives were subjected to diazotization
followed by azidation to obtain azide-substituted methyl lactisole derivatives 18 and 19, which were
checked by chiral center configuration. The methyl esters were hydrolyzed with sodium hydroxide
under reflux condition to afford 20 and 21 in high yields (Figure 3).
◦
Figure 3. Synthesis of 4- and 3- azide-substituted lactisole derivatives. (
10 min; (2) DEAD, CH2Cl2, rt, 8 h, (S)-14 99%, (R)-14 quant., (S)-15 quant., (R)-15 quant, (
CH3OH, rt, 2 h, (S)-16 quant., (R)-16 quant., (S)-17 quant., (R)-17 87%, (
(2) NaN3, 0 ◦C, 30 min, then rt, 30 min, (S)-18 quant., (R)-18 93%., (S)-19 92%., (R)-19 85%, (
CH3OH, H2O, reflux, 5 h, (S)-20 91%, (R)-20 96%, (S)-21 quant., (R)-21 81%.
a
) (1) PPh3, CH2Cl2, 0 C,
) H2, Pd/C,
c
) (1) NaNO2, HCl, H2O, 0 ◦C;
b
d) NaOH,
Then, 2-Nitrophenol 22 was also subjected to the Mitsunobu reaction in an identical manner
with another isomer to make nitro methyl lactate skeleton 23. The hydrogenation of the nitro
group promoted subsequent intramolecular cyclization between the amino and methyl ester to
afford 2-methyl-2H-benzo[b][1,4]oxazin-3(4H)-one as the sole product [27]. To prevent intramolecular
cyclization, the methyl ester hydrolyzed 24, then converted to tert-butyl ester 25. The hydrogenation
of nitro group of 25 proceeded smoothly to isolate aniline derivative 26 within an hour. Although
tert-butyl ester was selected, intramolecular cyclization between the aniline and ester proceeded with a
longer reaction time (>4 h). Compound 26 was subjected to diazotization followed by azidation to
construct phenylazide moiety 27, which was checked by chiral center configuration.
The deprotection of tert-butyl group of 27 with trifluoroacetic acid in dichloromethane afforded a
complex mixture because the azide group was not stable under this condition. Mild acidic deprotection
with 4 M HCl in dioxane was acceptable, but the partial decomposition of starting material 27 was
observed over an hour. The starting material 27 could be recovered by partition within 1 h, and the
hydrolysis was repeated for the recovered 27 three times to afford compound 28 in a moderate yield
(Figure 4). The reaction with 2-nitrophenol 22 and optical pure tert-butyl lactate was also conducted to
construct compound 25 directly, but unfortunately, the Mitsunobu reaction did not proceed for the
tert-butyl lactate.
2.1.3. Trifluotromethyldiazirine-Based Lactisole Derivatives
Todate, trifluoromethyldiazirine-basedlactisolederivativeshavenotbeenreported. Thethree-membered
azi (N=N) partial structure of trifluoromethyldiazirine is not stable for the Mitsunobu condition because
the reactant, diethyl azodicarboxylate DEAD also has an azo group in its structure. The reaction with
diazirinyl phenol derivatives and 10-hydroxy peracetylsucrose with DEAD or Tsuda reagents did not
occur in our previous study [14]. The synthetic plan was based on the preparation of trifluoroacetyl
modified on the aromatic ring of lactisole; then we constructed a diazirinyl three-membered ring
on the trifluoroacetyl group. The reagent of liquid ammonia is essential to the construction of the

Molecules 2020, 25, 2790
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diazirine moiety, but the reagent also reacts with methyl ester to form amide. tert-Butyl ester was
utilized for this purpose. p-Trifluoroacetyl anisole and m-trifluoroacetyl anisole 29 and 30 were selected
as the starting material for 4 and 3-substituted lactisoles. Compound 29 was treated with lithium
chloride under a reflux condition to obtain trifluoroacetyl phenol 31 [30,31]. m-Trifluoroacetyl phenol
32 was synthesized with a boron tribromide treatment of 30 at room temperature [32]. Mitsunobu
reactions for these phenols with chiral methyl lactate were archived in an identical manner to construct
lactisole methyl ester skeletons 33 and 34. After the hydrolysis of methyl esters with K2CO3 under the
reflux condition, corresponding trifluoroacetyl-substituted carboxylic acids 35 and 36 were subjected
to diazirine formation. However, it was difficult to construct diazirine moiety for 35 and 36 directly.
The carboxylic acids were converted to tert-butyl esters with tert-butyl bromide in the presence of
K2CO3 and tetrabutylammonium bromide (TBAB) under reflux conditions. Although the reactions
were not completed within 5 h, the decompositions of the diazirinyl moiety of the starting material
were observed over 5 h. tert-Butyl derivatives 37 and 38 were obtained with moderate yields and the
starting materials could be recovered from the reaction mixture (Figure 5). The tert-butyl thioester
formations [33] were also conducted for the carboxylic acids to improve the chemical yields of the
protection. The chemical yields were almost identical with tert-butyl ester, but the recovery of the
starting material was very difficult from the reaction mixture. Mitsunobu reactions for trifluoroacetyl
phenol 31 and 32 with chiral tert-butyl lactate were also conducted, but no reactions were observed.
Figure 4. Synthesis of 2-azide-substituted lactisole derivatives. (
(2) DEAD, CH2Cl2, rt, 8 h, (S)-23 quant., (R)-23 quant., ( ) NaOH, CH3OH, reflux, 1h, (S)-24 quant.,
(R)-24 quant., (c) t-Butyl bromide, K2CO3, tetrabutylammonium bromide, dimethyl acetamide, 55 ◦C,
a
) (1) PPh3, CH2Cl2, 0 ◦C, 10 min;
b
2.5 h, (S)-25 77%, (R)-25 82%, (
d
) H2, Pd/C, CH3OH, rt, 1 h, (S)-26 73%, (R)-26 89%, (
e
) NaNO2, HCl,
H2O, 0 ◦C; (2) NaN3, 0 ◦C, 30 min, then rt, 30 min, (S)-27 quant., (R)-27 89%, (
1 h, (S)-28 68%, (R)-26 65%.
f) 4 M HCl, dioxane, rt,
Figure 5. Synthesis of 3- and 4-trifluoroacetyl lactisole derivatives. (
82%, BBr3, CH2Cl2, rt, 2 h for 32 quant. (
) (1) PPh3, CH2Cl2, 0 ◦C, 10 min; (2) DEAD, CH2Cl2, rt,
8 h, (S)-33 78%, (R)-33 74%, (S)-34 71%, (R)-34 75%. ( ) K2CO3, MeOH, H2O, reflux, 2 h, (S)-35 quant.,
(R)-35 95%, (S)-36 99%, (R)-36 97%. ( ) t-BuBr, K2CO3, tetrabutylammonium bromide (TBAB), DMA,
55 ◦C, 5 h, (S)-37 66%, (R)-37 70%, (S)-38 38%, (R)-38 37%.
a) LiCl, DMF, reflux, 5 h for 31
b
c
d

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Then, 2-trifluoroactyl phenol, which was prepared by the Fries rearrangement of phenyl
2,2,2-trifluoroacetate with AlCl3 [34], was subjected to Mitsunobu reaction with chiral methyl lactate
and did not afford a 2-trifluoroacetyl lactisole skeleton. The Mitsunobu reaction of salicylaldehyde and
methyl lactate followed by the conversion of aldehyde to the trifluoroacetyl group also failed due to
4
4
the instability of methyl ester for the condition of trifluoroacetyl construction. Protected salicylaldehyde
was selected for trifluoroacetyl substitution at the 2-position of lactisole. The carbonyl group was
protected by thioacetal 40
[35], then subjected to a Mitsunobu reaction with chiral methyl lactate 4
and to construct lactisole methyl ester 41 in an identical manner to that described above. After
5
the hydrolysis of methyl esters with methanolic NaOH under the reflux condition, carboxylic acid
42 was converted to lactisole tert-butyl ester 43, then thioacetal was deprotected with methyl iodide.
Aldehyde 44 was treated with TMS-CF3 followed by oxidation with Dess–Martin periodinane [20] to
afford 2-trifluoroacetyl-substituted lactisole tert-butyl ester 45 (Figure 6).
Figure 6. Synthesis of 2-trifluoroacetyl lactisole derivative. (
95%, ( ) (1) or
, PPh3, CH2Cl2, 0 ◦C, 10 min; (2) DEAD, CH2Cl2, rt, 8 h, (S)-41 98%, (R)-41 98%,
) K2CO3, MeOH, H2O, reflux, 1 h, (S)-42 quant., (R)-42 quant, (
) t-BuBr, K2CO3, TBAB, DMA, 55 ◦C,
2.5 h, (S)-43 83%, (R)-43 82%, ( ) CH3I, NaHCO3, CH3CN, H2O, rt, 24 h, (S)-44 78%, (R)-44 79%,
) (1) TMS-CF3, K2CO3, DMF, rt, 4 h, (2) 1 M HCl, rt, 4 h; (3) Dess–Martin periodinane, CH2Cl2, rt, 3 h,
(S)-45 85%, (R)-45 89%.
a) 1,3-propanedithiol, I2, CH2Cl2, rt, 1 h,
b
4
5
(c
d
e
(f
Each trifluoroacetyl-substituted lactisole tert-butyl esters (37
constructions, oximation with hydroxylamine hydrochloride 46 48, tosylation for hydroxyl group of
oxime 49 51, diaziridine formation with liquid ammonia 52 54, and oxidation with activated MnO2 to
obtain 55 57, which were checked by chiral center configuration. tert-Butyl esters were hydrolyzed
with trifluoroacetic acid to afford trifluoromethyldiazirine-based lactisole derivatives in moderate
, 38, 45) was subjected to diazirine
–
–
–
–
yields. The one-pot conversion of the tosyl oxime 49 to diazirine 55 [36] was also acceptable for the
preparation with an identical yield (Figure 7).
2.2. Cell-Based Sweet Taste Assay
The synthesized photoreactive lactisole derivatives were administrated to the Flp-In 293 cell line
and were expressed as inhibitors to the human sweet taste receptors, with less than 3.2 mM comprising
the final concentration. (S)-configurations of all photoreactive lactisole derivatives were preferred
for sweet taste inhibition, and the results were consistent with our previous studies for lactisole and
2,4-dichlorophenoxy propanoic acid (2,4-DP) [
substitute for sweet taste receptors. Azide-substituted lactisoles (20
linear linkage of three nitrogen atoms, had slightly higher affinity for the receptor than benzophenone
derivatives. Trifluoromethyldiazirinyl substitution (58 60) had the highest affinity for sweet taste
5
]. Benzophenone photophore (9–11) is too bulky to
,
21 and 28), which feature the
–
receptors among the photoreactive lactisole derivatives. The positions of photophores on aromatic
rings are also influenced the activity, and the 4-position was preferred as a substitute. Fifty percent
inhibitory concentration (IC50) values (
µM) for (S)-58 and (S)-59 are almost identical with that of
(S)-lactisole (Table 1, Supplementary Materials).

Molecules 2020, 25, 2790
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Figure 7. Synthesis of 2-, 3- and 4-trifluoromethyl diazirinyl lactisole derivatives. (
pyridine, EtOH, 60 ◦C, 12 h, (S)-46 quant., (R)-46 quant., (S)-47 quant., (R)-47 85%, (S)-48 quant., (R)-48
98%, ( ) Tosyl chloride, DMAP, CH2Cl2, rt, 45 min, (S)-49 quant., (R)-49 98%, (S)-50 quant., (R)-50 93%,
(S)-51 94%, (R)-51 quant., ( ) NH3 (l), Et2O, rt, 12 h, (S)-52 88%, (R)-52 88%, (S)-53 92%, (R)-53 quant.,
(S)-54 76%, (R)-54 80%, (d) MnO2, CH2Cl2, rt, 2 h, (S)-55 91%, (R)-55 92%, (S)-56 82%, (R)-56 82%,
(S)-57 89%, (R)-57 96%, ( ) CF3COOH, CH2Cl2, rt, 4 h, (S)-58 98%, (R)-58 92%, (S)-59 quant., (R)-59
a) NH2OH HCl,
b
c
e
89%, (S)-60 quant., (R)-60 quant.
Table 1. Inhibitoryactivitiesofphotophorecontaininglactisolederivatives. IC50: 50%inhibitoryconcentration.
Position of
Photophore
Benzophenone
IC50 (µM)
Azide IC50 (µM)
Diazirine IC50 (µM)
(S)-9
(R)-9
970 ± 11
2200 ± 32
1100 ± 10
1100 ± 11
1200 ± 20
1200 ±18
82 ± 0.44
7.9 ± 0.067
(S)-20
(R)-20
(S)-21
(R)-21
(S)-28
(R)-28
(S)-61
(S)-62
100 ± 0.77
1800 ± 24
100 ± 0.83
2400 ± 23
280 ± 5.2
1200 ± 18
20 ± 4.3
(S)-58
(R)-58
(S)-59
(R)-59
(S)-60
(R)-60
(R)-61
(R)-62
12 ± 0.067
250 ± 1.8
19 ± 0.14
250 ± 1.7
37 ± 0.28
300 ± 1.8
nd
4-
(S)-10
3-
2-
(R)-10
(S)-11
(R)-11
rac-lactisole 61
rac-2,4-DP 62
Control
2.6 ± 0.51
45 ± 6.1
nd: not determined.
3. Discussion
The 2-phenoxypropanoic acid skeleton has a unique bioactivity and is known as a pesticide
and sweetener inhibitor. It seems that the stereochemistry at the 2-position may play an important
role in its biological activity. We reported a comparison of the biological activity of optically pure
lactisole and 2,4-dichlorophenoxy propanoic acid, which were synthesized in an asymmetric manner.
Photoaffinity labeling is one of the most reliable methods for functional analysis between small
ligands and biomolecules. It is essential to prepare photophore-substituted ligand derivatives. In this
paper, we achieved the asymmetric synthesis of benzophenone, azide and trifluoromethyldiazirine
modified derivatives on the aromatic ring of lactisole. The Mitsunobu reaction was utilized to
construct a lactisole skeleton in an asymmetric manner. Although benzophenone skeletons were
acceptable for the Mitsunobu reaction conditions, azide and trifluoromethyldiazirine moieties are
not suitable for the condition because of the nitrogen–nitrogen multiple bonds in their structures.
The phenol derivatives of precursors for these photophores were utilized for the asymmetric synthesis
of the lactisole skeleton, followed by the construction of photophores on these derivatives. Several
instabilities of the intermediates to the reaction condition were found, which were overcome with
improvements of the reaction condition or protecting groups. Human sweet receptor assays for the
photophore-containing lactisole derivatives revealed that (S)-isomers at the 4-position of lactisole

Molecules 2020, 25, 2790
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derivatives are important and that the trifluoromethyldiazirine-substituted derivatives have identical
affinity to optically pure lactisole. These results indicated that photoaffinity labeling with synthetic
lactisole derivatives will be useful for the functional analysis of sweet taste receptors.
4. Materials and Methods
4.1. General Procedures
All reagents used were of analytical grade. Nuclear magnetic resonance (NMR) spectra were
measured by an EX 270 spectrometer (JEOL, Tokyo, Japan). Optical rotations were measured at 23 ◦C
on a JASCO DIP370 polarimeter (JASCO, Tokyo, Japan). HRMS-ESI spectra were obtained with a
Waters (Waters, Milford, CT, USA). Chiral lactisoles ((S)- and (R)-61) and 2,4-DPs ((S)- and (R)-62) were
synthesized previously [5]. The chirality of ester derivatives was determined by a Chiralcel IG column
(250 × 4.6 mm) with n-hexane and 2-propanol.
4.2. Synthesis of Benzophenone-Based Lactisole Derivatives
Methyl (S)-2-(4-benzoylphenoxy)propanoate ((S)-6). To 4-hydroxybenzophenone
1 (182 mg,
0.92 mmol) in dry CH2Cl2 (6 mL), methyl D-(+)-lactate
4 (144 mg, 1.38 mmol) and PPh3 (290 mg,
1.10 mmol) was added at 0 ◦C. After the reaction mixture was stirred for 10 min at 0 ◦C, DEAD (240 mg,
1.38 mmol) was slowly added at same temperature. The reaction mixture was stirred overnight at room
temperature and partitioned between water and CH2Cl2. The organic layer was washed with brine,
dried over MgSO4, filtered and concentrated. The residue was purified by column chromatography
(ethyl acetate/n-hexane, 1:9) to give methyl (S)-2-(4-benzoylphenoxy)propanoate ((S)-
6
) (230 mg, 88%).
1
[
α
]
−
42 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.81 (d, J = 8.6 Hz, 2H), 7.75 (d, J = 7.4 Hz, 2H),
D
7.56 (t, J = 7.4 Hz, 1H), 7.46 (t, J = 7.4 Hz, 2H), 6.93 (d, J = 8.6 Hz, 2H), 4.87 (q, J = 6.8 Hz, 1H), 3.78 (s, 3H),
1.67 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 195.4, 171.9, 161.0, 138.0, 132.5, 131.9, 130.9,
129.7, 128.1, 114.4, 72.4, 52.4, 18.3. HRMS (ESI): m/z calculated for C17H16O4 + H+ [M + H+]: 285.1127.
Found: 285.1120. Chiral HPLC (n-hexane/2-propanol 90:10): tR 25.8 min.
Methyl(R)-2-(4-benzoylphenoxy)propanoate((R)-6). The similar treatment of 4-hydroxybenzophenone
1
(361 mg, 1.82 mmol) and methyl L-(
−
)-lactate
5
(284 mg, 2.72 mmol) as that just described gave (R)-
6
1
(542 mg, quant). [
α
]
D +42 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.80 (d, J = 8.9 Hz, 2H), 7.74 (d,
J = 7.3 Hz, 2H), 7.55 (t, J = 7.3 Hz, 1H), 7.46 (t, J = 7.3 Hz, 2H), 7.46 (t, J = 7.3 Hz, 2H), 6.92 (d, J = 8.9 Hz,
2H), 4.87 (q, J = 6.8 Hz, 1H), 3.77 (s, 3H), 1.66 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 195.2,
171.9, 160.9, 138.0, 132.4, 131.9, 130.8, 129.6, 128.2, 114.3, 72.3, 52.3, 18.3. HRMS (ESI): m/z calculated
for C17H16O4 + H+ [M + H+]: 285.1127. Found: 285.1132. Chiral HPLC (n-hexane/2-propanol 90:10):
tR 28.0 min.
Methyl(S)-2-(3-benzoylphenoxy)propanoate((S)-7). Thesimilartreatmentof3-hydroxybenzophenone
2
(200 mg, 1.01 mmol) and methyl D-(+)-lactate
4
(157 mg, 1.51 mmol) as that just described gave (S)-
7
(288 mg, quant). [
α
]
−
28 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ
= 7.79 (d, J = 7.4 Hz, 2H),
D
7.59 (t, J = 7.4 Hz, 1H), 7.47 (t, J = 7.4 Hz, 2H), 7.38 (m, 2H), 7.30 (m, 1H), 7.12 (m, 1H), 4.83 (q, J = 6.8 Hz,
1H), 3.76 (s, 3H), 1.64 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3): δ = 196.1, 172.2, 157.4, 138.9,
137.4, 132.4, 130.0, 129.4, 128.2, 123.5, 119.6, 115.8, 72.5, 52.3, 18.4. HRMS (ESI): m/z calculated
for C17H16O4 + H+ [M + H+]: 285.1127. Found: 285.1127. Chiral HPLC (n-hexane/2-propanol
90:10): tR 19.6 min.
Methyl (R)-2-(3-benzoylphenoxy)propanoate ((R)-7). The similar treatment of 3-hydroxybenzophenone
2
(360 mg, 1.82 mmol) and methyl L-(
−
)-lactate
5
(284 mg, 2.72 mmol) as that just described gave (R)-
7
1
(517 mg, quant). [
α
]D +28 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.71 (d, J = 7.4 Hz, 2H), 7.51 (t,
J = 7.4 Hz, 1H), 7.39 (t, J = 7.4 Hz, 2H), 7.31 (m, 2H), 7.22 (m, 1H), 7.04 (m, 1H), 4.75 (q, J = 6.8 Hz, 1H),
3.68 (s, 3H), 1.56 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 196.1, 172.2 157.4, 138.9, 137.4,
132.4, 129.7, 128.2, 123.5, 119.6, 115.9, 72.6, 52.3, 18.5. HRMS (ESI): m/z calculated for C17H16O4 + H+
[M + H+]: 285.1127. Found: 285.1122. Chiral HPLC (n-hexane/2-propanol 90:10): tR 18.9 min.

Molecules 2020, 25, 2790
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Methyl (S)-2-(2-benzoylphenoxy)propanoate ((S)-8). The similar treatment of 2-hydroxybenzophenone
3
(S)-
(210 mg, 1.06 mmol) and methyl D-(+)-lactate
4
(165 mg, 1.59 mmol) as that just described gave
1
8
(263 mg, 88%). [
α
]D +11 (c 1, CHCl3). H-NMR (270 MHz, CDCl3): δ = 7.84 (2H, d, J = 8.2 Hz)
,
7.54 (1H, t, J = 7.4 Hz), 7.43 (1H, d, J = 7.6 Hz), 7.42 (3H, t, J = 7.4 Hz), 7.08 (1H, t, J = 7.4 Hz),
6.80 (1H, d, J = 8.2 Hz), 4.66 (1H, q, J = 6.8 Hz), 3.68 (3H, s), 1.24 (3H, d, J = 6.8 Hz). 13C-NMR
(67.5 MHz, CDCl3):
δ = 196.3, 172.0, 155.3, 138.0, 132.7, 131.9, 130.0, 129.7, 129.7, 128.0, 121.6, 113.0,
73.2, 52.2, 18.0. HRMS (ESI): m/z calculated for C17H16O4 + H+ [M + H+]: 285.1127. Found: 285.1119.
Chiral HPLC (n-hexane:2-propanol = 90:10) tR 15.4 min.
Methyl (R)-2-(2-benzoylphenoxy)propanoate ((R)-8). The similar treatment of 2-hydroxybenzophenone
3
(372 mg, 1.87 mmol) and methyl L-(
−
)-lactate
−
5 (293 mg, 2.81 mmol) as that just
described gave (R)- (435 mg, 82%).
8
[
α
]
11 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
D
δ = 7.83 (d, J = 8.2 Hz, 2H), 7.54 (t, J = 7.4 Hz, 1H), 7.43 (d, J = 7.6 Hz, 1H), 7.42 (t, J = 7.9 Hz, 3H), 7.08
(t, J = 7.4 Hz, 1H), 6.80 (d, J = 8.2 Hz, 1H), 4.66 (q, J = 6.8 Hz, 1H), 3.68 (s, 3H), 1.24 (d, J = 6.8 Hz, 3H).
13C-NMR (67.5 MHz, CDCl3):
δ = 196.3, 172.0, 155.3, 138.0, 132.7, 131.8, 130.0, 129.7, 129.7, 128.0, 121.6,
113.0, 73.2, 52.1, 17.9. HRMS (ESI): m/z calculated for C17H16O4 + H+ [M + H+]: 285.1127. Found:
285.1132. Chiral HPLC (n-hexane:2-propanol = 90:10) tR 17.7 min.
(S)-2-(4-benzoylphenoxy)propanoic acid ((S)-9). Methyl (S)-2-(4-benzoylphenoxy)-propanoate
(S)-6 (212 mg, 0.75 mmol) was dissolved in MeOH (14.4 mL) and H2O (1.6 mL), and then K2CO3
(309 mg, 2.24 mmol) was added. After the reaction mixture was stirred at reflux for 2 h, cooled to room
temperature and then partitioned between ethyl acetate and water. The water layer was acidified by 1 M
HCl and extracted by ethyl acetate. The organic layer was washed by H2O and brine, and dried over
MgSO4, filtrated and concentrated to give (S)-2-(2-benzoylphenoxy)propanoic acid (S)-
9
(206 mg, quant).
1
[
α
]
−
22 (c 1, CHCl3). H-NMR (270 MHz, CDCl3): δ = 7.82 (d, J = 8.9 Hz, 2H)
,
7.75 (d, J = 7.4 Hz, 2H)
,
D
7.57 (t, J = 7.4 Hz, 1H), 7.47 (t, J = 7.4 Hz, 2H), 6.95 (d, J = 8.9 Hz, 2H), 4.91 (q, J = 6.8 Hz, 1H), 1.72
(d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 195.9, 176.4, 160.9, 137.8, 132.6, 132.1, 130.8,
129.8, 128.2, 114.4, 71.9, 18.3. HRMS (ESI): m/z calculated for C16H14O4 + H+ [M + H+]: 271.0970
.
Found: 271.0970.
(R)-2-(4-benzoylphenoxy)propanoic acid ((R)-9).
(R)-2-(4-benzoylphenoxy)propanoate (R)- (517 mg, 1.82 mmol) as that just described gave (R)-
(511 mg, quant). [ = 7.82 (d, J = 8.9 Hz, 2H),
+22 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
7.75 (d, J = 7.4 Hz, 2H), 7.57 (t, J = 7.4 Hz, 1H), 7.47 (t, J = 7.4 Hz, 2H), 6.96 (d, J = 8.9 Hz, 2H),
The similar treatment of methyl
6
9
α
]
δ
D
4.91 (q, J = 6.8 Hz, 1H), 1.72 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 196.0, 175.8, 161.0,
137.8, 132.6, 132.1, 130.8, 129.8, 128.2, 114.5, 72.0, 18.3. HRMS (ESI): m/z calculated for C16H14O4 + H+
[M + H+]: 271.0970. Found: 271.0950.
(S)-2-(3-benzoylphenoxy)propanoic acid ((S)-10).
(S)-2-(3-benzoylphenoxy)propanoate (S)- (159 mg, 0.56 mmol) as that just described gave (S)-10
(144 mg, 95%). [ = 7.78 (d, J = 7.3 Hz, 2H),
9 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
7.57 (t, J = 7.3 Hz, 1H), 7.46 (t, J = 7.3 Hz, 2H), 7.40 (m, 2H), 7.3 (m, 1H), 7.15 (m, 1H), 4.88 (q, J = 6.8 Hz,
The similar treatment of methyl
7
α
]
−
δ
D
1H), 1.68 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 196.3, 177.0, 157.2, 139.0, 137.3, 132.6, 130.0,
129.6, 128.3, 123.9, 119.7, 116.0, 72.1, 18.3. HRMS (ESI): m/z calculated for C16H14O4 + H+ [M + H+]
271.0970. Found: 271.0952. Chiral HPLC (n-hexane:2-propanol = 90:10) tR 25.8 min.
:
(R)-2-(3-benzoylphenoxy)propanoic acid ((R)-10).
(R)-2-(3-benzoylphenoxy)propanoate (R)- (413 mg, 1.45 mmol) as that just described gave (R)-10
(465 mg, quant). [ = 7.78 (d, J = 7.4 Hz,
+9 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
2H), 7.57 (t, J = 7.4 Hz, 1H), 7.45 (t, J = 7.4 Hz, 2H), 7.39 (m, 2H), 7.33 (m, 1H), 7.14 (m, 1H),
4.88 (q, J = 6.8 Hz, 1H), 1.68 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
= 196.5, 176.5,
The similar treatment of methyl
7
α
]
δ
D
δ
157.2, 138.8, 137.2, 132.6, 130.0, 129.5, 128.2, 123.8, 119.7, 115.9, 72.1, 18.3. HRMS (ESI): m/z calculated
for C16H14O4 + H+ [M + H+]: 271.0970. Found: 271.0960. Chiral HPLC (n-hexane:2-propanol = 90:10)
tR 28.0 min.

Molecules 2020, 25, 2790
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(S)-2-(2-benzoylphenoxy)propanoic acid ((S)-11).
The similar treatment of methyl
(S)-2-(3-benzoylphenoxy)propanoate (S)-
(187 mg, 87%). [
7.64 (t, J = 7.3 Hz, 1H), 7.50 (m, 4H), 7.12 (m, 2H), 5.00 (q, J = 6.8 Hz, 1H), 1.65 (d, J = 6.8 Hz, 3H).
13C-NMR (67.5 MHz, CDCl3):
= 197.1, 173.1, 156.6, 137.0, 133.8, 132.1, 130.7, 128.5, 127.3, 121.9, 115.1,
75.2, 18.6. HRMS (ESI): m/z calculated for C16H14O4 + H+ [M + H+]: 271.0970. Found: 271.0950.
(R)-2-(2-benzoylphenoxy)propanoic acid ((R)-11). The similar treatment of methyl
(S)-2-(2-benzoylphenoxy)propanoate (R)- (392 mg, 1.38 mmol) as that just described gave (R)-11
(326 mg, 88%). [ = 7.87 (d, J = 6.9 Hz, 2H),
+40 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
7.64 (t, J = 7.4 Hz, 1H), 7.50 (m, 4H), 7.12(m, 2H), 5.01 (q, J = 6.9 Hz, 1H), 1.66 (d, J = 6.9 Hz, 3H).
8
(229 mg, 0.80 mmol) as that just described gave (S)-11
α
]
−
40 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 7.87 (d, J = 7.3 Hz, 2H),
D
δ
8
α
]
δ
D
13C-NMR (67.5 MHz, CDCl3):
δ = 197.1, 173.0, 156.6, 137.0, 133.8, 132.1, 130.7, 128.5, 127.3, 121.9, 115.0,
75.2, 18.6. HRMS (ESI): m/z calculated for C16H14O4 + H+ [M + H+]: 271.0970. Found: 271.0950.
4.3. Synthesis of 3- or 4-Azidephenoxy-Based Lactisole Derivatives
Methyl (S)-2-(4-nitrophenoxy)propanoate ((S)-14). To 4-nitrophenol 12 (437 mg, 3.14 mmol) in
dry CH2Cl2 (6 mL), D-(+)-lactate
4 (491 mg, 4.71 mmol) and PPh3 (989 mg, 3.77 mmol) was added
at 0 ◦C After the reaction mixture was stirred for 10 min at 0 ◦C, DEAD (820 mg, 4.71 mmol) was
slowly added at same temperature. The reaction mixture was stirred overnight at room temperature
and partitioned between water and CH2Cl2. The organic layer was washed with brine, dried over
MgSO4, filtered and concentrated. The residue was purified by column chromatography (ethyl
acetate/n-hexane, 1:9) to give (S)-14 (700 mg, 99%). [
α
]
−
64 (c 1, CHCl3). 1H-NMR (270 MHz,
D
CDCl3): δ = 8.20 (d, J = 8.9 Hz, 2H), 6.93 (d, J = 8.9 Hz, 2H), 4.88 (q, J = 6.8 Hz, 1H), 3.78 (s, 3H),
1.68 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 171.4, 162.4, 142.0, 125.9, 114.9, 72.9, 52.6,
18.4. HRMS (ESI): m/z calculated for C10H11NO5 + H+ [M + H+]: 226.0715. Found: 226.0720.
Methyl (R)-2-(4-nitrophenoxy)propanoate ((R)-14). The similar treatment of 4-nitrophenol 12
(128 mg, 0.92 mmol) and methyl L-(
(213 mg, quant). [ +64 (c 1, CHCl3), (ref. [
CDCl3): = 8.18 (d, J = 8.6 Hz, 2H), 6.93 (d, J = 9.2 Hz, 2H), 4.90 (q, J = 6.8 Hz, 1H), 3.78 (s, 3H), 1.68
d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
−
)-lactate
5
(144 mg, 1.38 mmol) as that just described gave (R)-14
α]
D
α
]
+64.4 (c 0.10, CHCl3) [29]). 1H-NMR (270 MHz,
D
δ
δ
= 171.2, 162.3, 141.9, 125.8, 114.8, 72.7, 52.5, 18.2.
HRMS (ESI): m/z calculated for C10H11NO5 + H+ [M + H+]: 226.0715. Found: 226.0720.
Methyl (S)-2-(3-nitrophenoxy)propanoate ((S)-15). The similar treatment of 3-nitrophenol 13
(301 mg, 2.16 mmol) and methyl D-(+)-lactate
4
(338 mg, 3.24 mmol) as that just described gave (S)-15
= 7.85 (dd, J = 8.1, 2.3 Hz, 1H),
1
(490 mg, quant). [
α
]
−
59 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
D
7.69 (t, J = 2.3 Hz, 1H), 7.44 (t, J = 8.1 Hz, 1H), 7.22 (dd, J = 8.1, 2.3 Hz, 1H), 4.87 (q, J = 6.8 Hz, 1H),
3.79 (s, 3H), 1.67 (d, J = 6.8 Hz, 3H). δ = 171.5, 158.0, 149.1, 130.1, 121.8,
13C-NMR (67.5 MHz, CDCl3):
116.5, 109.7, 72.9, 52.5, 18.3. HRMS (ESI): m/z calculated for C10H11NO5 + H+ [M + H+]: 226.0715.
Found: 226.0730.
Methyl (R)-2-(3-nitrophenoxy)propanoate ((R)-15). The similar treatment of 3-nitrophenol 13
(422 mg, 3.04 mmol) and methyl L-(
(711 mg, quant). [
−
)-lactate
5
(474 mg, 4.55 mmol) as that just described gave (R)-15
= 7.85 (dd, J = 8.2, 2.3 Hz, 1H),
1
α
]
D
+59 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
7.69 (t, J = 2.3 Hz, 1H), 7.44 (t, J = 8.2 Hz, 1H), 7.22 (dd, J = 8.2, 2.3 Hz, 1H), 4.87 (q, J = 6.8 Hz, 1H),
3.79 (s, 3H), 1.67 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 171.5, 158.0, 149.1, 130.1, 121.8,
116.5, 109.7, 72.9, 52.5, 18.3. HRMS (ESI): m/z calculated for C10H11NO5 + H+ [M + H+]: 226.0715.
Found: 226.0710.
Methyl (S)-2-(4-aminophenoxy)propanoate ((S)-16). Methyl (S)-2-(4-nitrophenoxy)-propanoate
(S)-15 (700 mg, 3.11 mmol) and 5% Pd/C (35.0 mg) were suspended in MeOH (10 mL). The reaction
mixture was stirred vigorously at room temperature for 2 h under H2 atmosphere. The residue was
1
filtrated using Celite and concentrated to give (S)-16 (607 mg, quant). [
(270 MHz, CDCl3):
3.73 (s, 3H), 3.46 (s, 2H), 1.57 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
α
]
−
50 (c 1, CHCl3). H-NMR
D
δ
= 6.73 (d, J = 8.9 Hz, 2H), 6.59 (d, J = 8.9 Hz, 2H), 4.63 (q, J = 6.8 Hz, 1H),
= 173.0, 150.4, 141.0,
δ

Molecules 2020, 25, 2790
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116.7, 116.1, 73.7, 52.1, 18.5. HRMS (ESI): m/z calculated for C10H13NO3 + H+ [M + H+]: 196.0974.
Found: 196.0960.
Methyl (R)-2-(4-aminophenoxy)propanoate ((R)-16). The similar treatment of methyl (R)-2-(4-
nitrophenoxy)propanoate (R)-15 (575 mg, 2.56 mmol) as that just described gave (R)-16 (500 mg, quant).
1
[α
]
D +50 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 6.73 (d, J = 8.9 Hz, 2H), 6.66 (d, J = 8.9 Hz, 2H),
4.64 (q, J = 6.8 Hz, 1H), 4.24 (s, 2H), 3.73 (s, 3H), 1.57 (3H, d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz,
CDCl3):
δ = 172.9, 151.0, 139.5, 116.9, 116.7, 73.6, 52.1, 18.5. HRMS (ESI): m/z calculated for C10H13NO3
+ H+ [M + H+]: 196.0974. Found: 196.0950.
Methyl (S)-2-(3-aminophenoxy)propanoate ((S)-17). The similar treatment of methyl (S)-2-(3-
nitrophenoxy)propanoate (S)-15 (490 mg, 2.17 mmol) as that just described gave (S)-17 (367 mg, 87%).
1
[
α
]
−
23 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.01 (t, J = 7.9 Hz, 1H), 6.28 (dd, J = 7.9, 1.0 Hz,
13C-NMR
= 172.7, 158.5, 147.9, 130.0, 108.7, 104.4, 102.1, 72.2, 52.1, 18.5. HRMS (ESI): m/z
calculated for C10H13NO3 + H+ [M + H+]: 196.0974. Found: 196.0980.
D
1H), 6.23 (m, 2H), 4.72 (q, J = 6.8 Hz, 1H), 3.73 (s, 3H), 3.68 (s, 3H), 1.58 (d, J = 6.8 Hz, 3H)
(67.5 MHz, CDCl3):
.
δ
Methyl (R)-2-(3-aminophenoxy)propanoate ((R)-17). The similar treatment of methyl (R)-2-(3-
nitrophenoxy)propanoate (R)-15 (628 mg, 2.78 mmol) as that just described gave (R)-17 (558 mg, quant).
1
[α
]
+23 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.05 (t, J = 7.9 Hz, 1H), 6.37 (d, J = 7.9 Hz, 1H),
D
6.25 (m, 2H), 4.73 (q, J = 6.8 Hz, 1H), 4.19 (s, 2H), 3.75 (s, 3H), 1.59 (d, J = 6.8 Hz, 3H). 13C-NMR
(67.5 MHz, CDCl3):
δ = 172.8, 158.6, 146.7, 130.2, 109.3, 105.3, 102.9, 72.4, 52.3, 18.5. HRMS (ESI): m/z
calculated for C10H13NO3 + H+ [M + H+]: 196.0974. Found: 196.0960.
Methyl (S)-2-(4-azidephenoxy)propanoate ((S)-18). Methyl (S)-2-(4-aminophenoxy)-propanoate
(S)-14 (607 mg, 3.11 mmol) was dissolved in water (6.78 mL) and 37◦% HCl (0.76 mL) at 0 ◦C. NaNO2
(237 mg, 3.44 mmol) in water (2.26 mL) was added slowly at 0 C, followed by NaN3 (381 mg,
5.87 mmol) in water (2.26 mL). After 30 min at 0 ◦C and 30 min at room temperature, the reaction
mixture was extracted with ethyl acetate. The organic layer was washed by brine, dried over MgSO4,
1
filtrated and concentrated to give (S)-18 (702 mg, quant). [
CDCl3):
1.61 (d, J = 6.8 Hz, 3H)
α
]
D
−
45 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 6.94 (d, J = 9.2 Hz, 2H), 6.86 (d, J = 9.2 Hz, 2H), 4.72 (q, J = 6.8 Hz, 1H), 3.76 (s, 3H),
.
13C-NMR (67.5 MHz, CDCl3):
δ
= 172.4, 154.9, 133.4, 120.1, 116.5, 73.0, 52.3,
18.5. HRMS (ESI): m/z calculated for C10H11N3O3 + H+ [M + H+]: 222.0879. Found: 222.0860. Chiral
HPLC (n-hexane/2-propanol 99:1): tR 20.5 min.
Methyl (R)-2-(4-azidephenoxy)propanoate ((R)-18). The similar treatment of methyl (R)-2-(4-
aminophenoxy)propanoate (R)-14 (500 mg, 2.56 mmol) as that just described gave (R)-18 (529 mg, 93%).
1
[α
]
D +45 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 6.94 (d, J = 9.2 Hz, 2H), 6.86 (d, J = 9.2 Hz, 2H)
,
4.73 (q, J = 6.8 Hz, 1H), 3.76 (s, 3H), 1.61 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 172.4,
154.9, 133.3, 120.1, 116.5, 73.0, 52.3, 18.5. HRMS (ESI): m/z calculated for C10H11N3O3 + H+ [M + H+]:
222.0879. Found: 222.0870. Chiral HPLC (n-hexane/2-propanol 99:1): tR 19.4 min.
Methyl (S)-2-(3-azidophenoxy)propanoate ((S)-19). The similar treatment of methyl (S)-2-(3-
aminophenoxy)propanoate (S)-17 (323 mg, 1.65 mmol) as that just described gave (S)-19 (336 mg, 92%).
[
α
]
−
28 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ
= 7.24 (t, J = 8.2 Hz, 1H), 6.65 (t, J = 8.2 Hz,
D
2H), 6.55 (s, 1H), 4.76 (q, J = 6.8 Hz, 1H), 3.76 (s, 3H), 1.62 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz,
CDCl3):
δ = 172.1, 158.6, 141.3, 130.5, 112.2, 111.1, 106.3, 72.5, 52.3, 18.4. HRMS (ESI): m/z calculated for
C10H11N3O3 + H+ [M + H+]: 222.0879. Found: 222.0880. Chiral HPLC (n-hexane/2-propanol 99:1):
tR 18.0 min.
Methyl (R)-2-(3-azidophenoxy)propanoate ((R)-19). The similar treatment of methyl (R)-2-(3-
aminophenoxy)propanoate (R)-17 (518 mg, 2.65 mmol) as that just described gave (R)-19 (497 mg, 85%).
[
α
]
+28 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ
= 7.24 (t, J = 8.1 Hz, 1H), 6.65 (t, J = 8.1 Hz,
D
1H), 6.55 (s, 1H), 4.76 (q, J = 6.8 Hz, 1H), 3.76 (s, 3H), 1.62 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz,
CDCl3):
δ = 172.0, 158.5, 141.2, 130.4, 112.0, 111.0, 106.2, 72.3, 52.1, 18.2. HRMS (ESI): m/z calculated for
C10H11N3O3 + H+ [M + H+]: 222.0879. Found: 222.0860. Chiral HPLC (n-hexane/2-propanol 99:1):
tR 16.7 min.

Molecules 2020, 25, 2790
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(S)-2-(4-Azidophenoxy)propanoic acid ((S)-20). Methyl (S)-2-(4-azidophenoxy)propanoate (S)-18
(702 mg, 3.17 mmol) was dissolved in MeOH (15 mL) and 2M NaOH (3.2 mL). After the reaction
mixture was stirred at reflux for 2 h, cooled to room temperature and then partitioned between
ethyl acetate and water. The water layer was acidified by 1 M HCl aq and extracted by ethyl acetate.
The organic layer was washed by H2O and brine, and dried over MgSO4, filtrated and concentrated
to give (S)-20 (601 mg, 91%). [α] δ = 9.68 (s, 1H),
+27 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
D
6.96 (d, J = 8.9 Hz, 4H), 6.89 (d, J = 8.9 Hz, 4H), 4.75 (d, J = 6.9 Hz, 1H), 1.66 (d, J = 6.9 Hz, 3H).
13C-NMR (67.5 MHz, CDCl3): δ = 177.6, 154.5, 133.7, 120.2, 116.6, 72.5, 18.4. HRMS (ESI): m/z calculated
for C9H9N3O3 + H+ [M + H+]: 208.0722. Found: 208.0720.
(R)-2-(4-Azidophenoxy)propanoic acid ((R)-20). The similar treatment of methyl (R)-2-(4-azido
phenoxy)propanoate (R)-18 (529 mg, 2.39 mmol) as that just described gave (R)-20 (475 mg, 96%).
[
α
]
−
27 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 11.71 (s, 1H), 6.93 (d, J = 8.9 Hz, 2H),
D
6.87 (d, J = 8.9 Hz, 2H), 4.74 (q, J = 6.8 Hz, 1H), 1.65 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 178.1, 154.5, 133.7, 120.1, 116.6, 72.5, 18.4. HRMS (ESI): m/z calculated for C9H9N3O3 + H+ [M + H+]:
208.0722. Found: 208.0710.
(S)-2-(3-Azidophenoxy)propanoic acid ((S)-21). The similar treatment of methyl (S)-2-(3-azide
phenoxy)propanoate (S)-19 (212 mg, 0.96 mmol) as that just described gave (S)-21 (211 mg, quant).
1
[α
]
D
−
5 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.26 (t, J = 8.1 Hz, 1H), 6.70 (dd, J = 8.1, 2.1 Hz,
1H), 6.66 (dd, J = 8.1, 2.1 Hz, 1H), 6.57 (t, J = 2.1 Hz, 1H), 4.80 (q, J = 6.8 Hz, 1H), 1.67 (d, J = 6.6 Hz, 3H).
13C-NMR (67.5 MHz, CDCl3):
δ = 177.5, 158.4, 141.6, 130.7, 112.5, 111.2, 106.5, 72.0, 18.3. HRMS (ESI):
m/z calculated for C9H9N3O3 + H+ [M + H+]: 208.0722. Found: 208.0750.
(R)-2-(3-Azidophenoxy)propanoic acid ((R)-21). The similar treatment of methyl (R)-2-(3-azido
phenoxy)propanoate (R)-19 (386 mg, 1.74 mmol) as that just described gave (R)-21 (294 mg, 81%).
1
[α]D +5 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ = 7.25 (t, J = 8.1 Hz, 1H), 6.69 (dd, J = 8.1, 2.1 Hz,
2H), 6.65 (dd, J = 8.1, 2.1 Hz, 2H), 6.57 (t, J = 2.1 Hz, 1H), 4.79 (q, J = 6.8 Hz, 1H), 1.66 (d, J = 6.8 Hz, 3H).
13C-NMR (67.5 MHz, CDCl3):
δ = 177.6, 158.4, 141.6, 130.7, 112.5, 111.2, 106.6, 72.0, 18.3. HRMS (ESI):
m/z calculated for C9H9N3O3 + H+ [M + H+]: 208.0722. Found: 208.0710.
4.4. Synthesis of 2-Azidephenoxy-Based Lactisole Derivatives
Methyl (S)-2-(2-nitrophenoxy)propanoate ((S)-23). The similar treatment of Mitsunobu reaction
for 2-nitrophenol 22 (509 mg, 3.66 mmol) and methyl D-(+)-lactate
4 (572 mg, 5.49 mmol) as that
just described gave (S)-23 (952 mg, quant). [
α
]
D
+106 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 7.83 (dd, J = 8.2, 1.6 Hz, 1H), 7.49 (td, J = 8.2, 1.6 Hz, 1H), 7.08 (td, J = 8.2, 1.2 Hz, 1H), 6.96 (dd,
J = 8.2, 1.2 Hz, 1H), 4.85 (q, J = 6.8 Hz, 1H), 3.76 (s, 3H), 1.69 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz,
CDCl3): δ = 171.1, 150.6, 140.5, 133.7, 125.4, 121.4, 115.6, 74.2, 52.3, 18.1. HRMS (ESI): m/z calculated for
C10H11NO5 + H+ [M + H+]: 226.0715. Found: 226.0705.
Methyl (R)-2-(2-nitrophenoxy)propanoate ((R)-23). The similar treatment of 2-nitrophenol 22
(500 mg, 3.60 mmol) and methyl L-(
(892 mg, quant). [ 106 (c 1, CHCl3). (ref. [
CDCl3):
6.89 (td, J = 8.2, 1.2 Hz, 1H), 4.79 (q, J = 6.8 Hz, 1H), 3.69 (s, 3H), 1.62 (d, J = 6.8 Hz, 3H). 13C-NMR
−
)-lactate
5
(562 mg, 5.40 mmol) as that just described gave (R)-23
1
α
]
−
α
]
−
126.86 (c 1.0, EtOH) [28]). H-NMR (270 MHz,
D
D
δ
= 7.76 (dd, J = 8.2, 1.6 Hz, 1H), 7.41 (td, J = 8.2, 1.6 Hz, 1H), 7.01 (td, J = 8.2, 1.2 Hz, 1H),
(67.5 MHz, CDCl3):
δ = 171.3, 150.8, 140.7, 133.8, 125.6, 121.5, 115.8, 74.5, 52.5, 18.3. HRMS (ESI): m/z
calculated for C10H11NO5 + H+ [M + H+]: 226.0715. Found: 226.0710.
(S)-2-(2-Nitrophenoxy)propanoic acid ((S)-24). Methyl (S)-2-(2-nitrophenoxy)propanoate (S)-23
(261 mg, 1.16 mmol) was dissolved in MeOH (15 mL) and 2 M NaOH (1.5 mL). After the reaction
mixture was stirred at reflux for 1 h, cooled to room temperature and then partitioned between ethyl
acetate and water. The water layer was acidified by 1 M HCl and extracted by ethyl acetate. The organic
layer was washed by H2O and brine, and dried over MgSO4, filtrated and concentrated to give (S)-24
1
(251 mg, quant). [
α
]D +5 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.84 (d, J = 8.2 Hz, 1H), 7.49
(t, J = 8.2 Hz, 1H), 7.07 (t, J = 8.2 Hz, 1H), 6.97 (d, J = 8.2 Hz, 1H), 4.88 (q, J = 6.8 Hz, 1H), 1.68 (d,

Molecules 2020, 25, 2790
12 of 25
J = 6.8 Hz, 3H)
.
13C-NMR (67.5 MHz, CDCl3):
δ
= 174.4, 150.4, 140.3, 134.4, 126.1, 122.2, 115.8, 74.4,
18.2. HRMS (ESI): m/z calculated for C9H9NO5 + H+ [M + H+]: 212.0559. Found: 212.0540.
(R)-2-(2-Nitrophenoxy)propanoic acid ((R)-24). The similar treatment of methyl (R)-2-(2-nitrop
henoxy)propanoate (R)-23 (632 mg, 2.81 mmol) as that just described gave (R)-24 (752 mg, quant).
[
α
]
−
5 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ
= 7.79 (d, J = 8.2 Hz, 1H), 7.45 (t, J = 8.2 Hz,
1H), 7.04 (t, J = 8.2 Hz, 1H), 6.95 (d, J = 8.2 Hz, 1H), 4.85 (q, J = 6.8 Hz, 1H), 1.66 (d, J = 6.8 Hz, 3H)
13C-NMR (67.5 MHz, CDCl3):
= 175.5, 150.5, 140.4, 134.3, 126.0, 122.0, 115.8, 74.1, 18.1. HRMS (ESI):
m/z calculated for C9H9NO5 + H+ [M + H+]: 212.0559. Found: 212.0560.
D
.
δ
tert-Butyl (S)-2-(2-nitrophenoxy)propanoate ((S)-25). To a solution of (S)-2-(2-nitrophenoxy)pro
panoic acid (S)-24 (251 mg, 1.19 mmol), potassium carbonate anhydride (4.11 g, 29.7 mmol) and
tetrabutylammonium bromide (384 mg, 1.19 mmol) in N,N-dimethylacetamide (6 mL), tert-butyl
bromide (7.81 g, 57.0 mmol) was added dropwise at 0 ◦C. The reaction mixture was stirred at 55 ◦C
for 2.5 h. After cooling to room temperature, the mixture was poured into cold water and extracted
with ethyl acetate. The organic layer was washed with H2O, brine, dried over MgSO4, filtrated and
evaporated. The residue was purified by column chromatography (ethyl acetate/n-hexane, 1:6) to give
1
(S)-25 (246 mg, 77%). [
α
]
+108 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.81 (d, J = 8.2 Hz,
D
1H), 7.48 (t, J = 8.2 Hz, 1H), 7.05 (t, J = 8.2 Hz, 1H), 6.96 (d, J = 8.2 Hz, 1H), 4.75 (q, J = 6.8 Hz, 1H),
1.65 (d, J = 6.8 Hz, 3H), 1.42 (s, 9H). 13C-NMR (67.5 MHz, CDCl3): δ = 169.9, 151.0, 140.5, 133.5, 125.5,
121.0, 115.4, 82.4, 74.6, 27.7, 18.1. HRMS (ESI): m/z calculated for C13H17NO5 + H+ [M + H+]: 268.1185.
Found: 268.1170.
tert-Butyl (R)-2-(2-nitrophenoxy)propanoate ((R)-25). The similar treatment of (R)-2-(2-nitrophe
noxy)propanoic acid (R)-24 (289 mg, 1.37 mmol) as that just described gave (R)-25 (301 mg,
82%). [α]D −108 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 7.72 (d, J = 8.6 Hz, 1H), 7.40 (t,
J = 7.9 Hz, 1H), 6.97 (t, J = 7.9 Hz, 1H), 6.87 (d, J = 8.6 Hz, 1H), 4.67 (q, J = 6.8 Hz, 1H), 1.56 (d, J = 6.8 Hz,
3H), 1.33 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ = 169.9, 151.0, 140.5, 133.5, 125.5, 121.0, 115.4, 82.4,
74.5, 27.7, 18.1. HRMS (ESI): m/z calculated for C13H17NO5 + H+ [M + H+]: 268.1185. Found: 268.1190.
tert-Butyl (S)-2-(2-aminophenoxy)propanoate ((S)-26). tert-Butyl (S)-2-(2-nitrophenoxy)-
propanoate (S)-25 (246 mg, 0.92 mmol) and 5% Pd/C (12.3 mg) were suspended in MeOH (20 mL).
The reaction mixture was stirred vigorously at room temperature for 45 min under H2 atmosphere then
was filtrated with Celite and concentrated. The residue was partitioned between ethyl acetate and 1 M
HCl, and then 1 M NaOH was added to make pH 10, then extracted by ethyl acetate. The organic layer
was washed by brine and dried over MgSO4, filtrated, and concentrated to give (S)-26 (159 mg, 73%).
1
[
α
]
+11 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 6.81 (t, J = 7.6 Hz, 1H), 6.73 (d, J = 7.6 Hz,
D
1H), 6.67 (m, 2H), 4.62 (q, J = 8 Hz, 1H), 3.83 (s, 2H), 1.60 (d, J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR
(67.5 MHz, CDCl3):
δ = 171.5, 145.5, 137.2, 122.2, 118.1, 115.6, 113.5, 81.7, 74.0, 27.9, 18.6. HRMS (ESI):
m/z calculated for C13H19NO3 + H+ [M + H+]: 238.1443. Found: 238.1440.
tert-Butyl (R)-2-(2-aminophenoxy)propanoate ((R)-26). The similar treatment of tert-butyl
(R)-2-(2-nitrophenoxy)propanoate (R)-25 (666 mg, 2.49 mmol) as that just described gave (R)-26
1
(524 mg, 89%). [
α
]
D
−
11 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 6.80 (t, J = 7.6 Hz, 1H), 6.68 (m,
3H), 4.62 (q, J = 6.8 Hz, 1H), 3.92 (s, 2H), 1.59 (d, J = 6.8 Hz, 3H), 1.43 (s, 9H). 13C-NMR (67.5 MHz,
CDCl3):
δ = 171.5, 145.5, 137.2, 122.2, 118.1, 115.5, 113.5, 81.7, 74.00, 27.9, 18.6. HRMS (ESI): m/z
calculated for C13H19NO3 + H+ [M + H+]: 238.1443. Found: 238.1430.
tert-Butyl (S)-2-(2-azidophenoxy)propanoate ((S)-27). tert-Butyl (S)-2-(2-aminophenoxy)-propanoate
(S)-26 (159 mg, 0.67 mmol) was dissolved in water (1.46 mL) and 37% hydrochloric acid (0.17 mL) at 0 ◦C.
NaNO2 (51.3 mg, 0.74 mmol) in water (0.49 mL) was added slowly at 0 ◦C, followed by NaN3 (82.4 mg,
1.27 mmol) in water (0.49 mL). After 30 min at 0 ◦C and 30 min at room temperature, the reaction
mixture was extracted with ethyl acetate. The organic layer was washed by brine, dried over MgSO4,
1
filtrated and concentrated to give (S)-27 (194 mg, quant). [
CDCl3):
(s, 9H). 13C-NMR (67.5 MHz, CDCl3):
α
]
D +15 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 6.90 (m, 3H), 6.72 (d, J = 7.9 Hz, 1H), 4.62 (q, J = 6.8 Hz, 1H), 1.55 (d, J = 6.8 Hz, 3H), 1.34
= 170.6, 150.5, 128.9, 125.3, 122.1, 121.0, 114.1, 82.1, 74.1, 27.8,
δ

Molecules 2020, 25, 2790
13 of 25
18.1. HRMS (ESI): m/z calculated for C13H17N3O3 + H+ [M + H+]: 264.1348. Found: 264.1360. Chiral
HPLC (n-hexane/2-propanol 199:1): tR 37.8 min.
tert-Butyl (R)-2-(3-azidophenoxy)propanoate ((R)-27). The similar treatment of tert-butyl
(R)-2-(2-aminophenoxy)propanoate (R)-26 (524 mg, 2.21 mmol) as that just described gave ((R)-39)
1
(517 mg, 89%). [
α
]
D
−
15 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 6.92 (m, 3H), 6.77 (d, J = 7.9 Hz
,
1H), 4.67 (q, J = 6.8 Hz, 1H), 1.61 (d, J = 6.8 Hz, 3H), 1.39 (s, 9H). 13C-NMR (67.5 MHz, CDCl3): δ = 170.7
,
150.5, 128.9, 125.3, 122.1, 121.0, 114.2, 82.1, 74.1, 27.8, 18.1. HRMS (ESI): m/z calculated for C13H17N3O3
+ H+ [M + H+]: 264.1348. Found: 264.1330.
(S)-2-(2-Azidophenoxy)propanoic acid ((S)-28). tert-Butyl (S)-2-(2-azidophenoxy)-propanoate
((S)-27) (218 mg, 0.83 mmol) was dissolved in 4 M HCl in dioxane (7.5 mL) and stirred at room
temperature for 1 h, poured into 1 M NaOH solution to make alkaline. The organic layer was dried
over MgSO4, filtrated and concentrated, and then the residue was treated with the same reaction 2
times. The aqueous layer was extracted with ethyl acetate. The organic layer was dried over MgSO4,
1
filtrated and concentrated to give (S)-28 (116.3 mg, 68%). [
CDCl3):
J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
α
]
D +12 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 8,24 (s, 1H), 7.02 (m, 3H), 6.85 (d, J = 7.6 Hz, 1H), 4.81 (q, J = 6.8 Hz, 1H), 1.71 (d,
δ
= 176.4, 149.4, 129.5, 125.6, 123.1, 120.8, 115.2, 73.7,
18.2. HRMS (ESI): m/z calculated for C9H9N3O3 + H+ [M + H+]: 208.0722. Found: 208.0705. Chiral
HPLC (n-hexane/2-propanol 199:1): tR 42.9 min.
(R)-2-(2-Azidophenoxy)propanoic acid ((R)-28).
The similar treatment of tert-butyl
(R)-2-(2-azidephenoxy)propanoate ((R)-27) (253 mg, 0.96 mmol) as that just described gave (R)-28
1
(128.7 mg, 65%). [
α
]
−
12 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 9.31 (s, 1H), 7.09–6.96 (m,
D
3H), 6.84 (d, J = 7.6 Hz, 1H), 4.81 (q, J = 6.8 Hz, 1H), 1.70 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz,
CDCl3): δ = 176.9, 149.5, 129.4, 125.5, 123.0, 120.8, 115.1, 73.6, 18.2. HRMS (ESI): m/z calculated for
C9H9N3O3 + H+ [M + H+]: 208.0722. Found: 208.0715.
4.5. Synthesis of Trifluoromethyldiazirine-Based Lactisole Derivatives
2,2,2-Trifluoro-1-(4-hydroxyphenyl)ethan-1-one 31. 2,2,2-Trifluoro-1-(4-methoxyphenyl)-ethan-1
-one 29 (493 mg, 2.41 mmol) and lithium chloride (950 mg, 22.4 mmol) was dissolved in dry DMF
(7.5 mL). After the reaction mixture was stirred at reflux for 6 h, the mixture was cooled to room
temperature and 1 M HCl was added, and then extracted with ethyl acetate. The organic layer was
washed with brine and dried over MgSO4, filtrated and concentrated. The residue was purified by
1
column chromatography (ethyl acetate/n-hexane, 1:8) to give 31 (376 mg, 82%). H-NMR (270 MHz,
CDCl3):
δ
= 8.04 (d, J = 8.9 Hz, 2H), 6.96 (d, J = 8.9 Hz, 2H), 5.71 (s, 1H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 179.0 (q, 2JCF = 34.6 Hz), 133.1, 123.1, 116.9 (q, 1JCF = 291.6 Hz), 116.0. HRMS (ESI): m/z calculated
for C8H5F3O2 + H+ [M + H+]: 191.0320. Found: 191.0317.
2,2,2-Trifluoro-1-(3-hydroxyphenyl)ethan-1-one 32. 2,2,2-Trifluoro-1-(4-methoxyphenyl)-ethan-1
-one 30 (1.052 g, 5.15 mmol) was dissolved in CH2Cl2 (30 mL) and cooled to
78 ◦C. BBr3 was added
−
dropwise at
78 ◦C and the reaction mixture stirred at room temperature for 5 h. The mixture was
−
cooled to 0 ◦C and 10% NaOH (30 mL) was added slowly, and then HCl was added to make pH 1 at same
temperature. NH4OH was also added to make pH 7 at room temperature, then extracted by ethyl acetate.
1
The organic layer was dried over MgSO4, filtrated and concentrated to give 31 (1.018 g, quant). H-NMR
(270 MHz, CDCl3):
δ = 7.63 (d, J = 7.8 Hz, 1H), 7.50 (s, 1H), 7.41 (t, J = 7.8 Hz, 1H), 7.18 (dd, J = 7.8,
2.6 Hz, 1H). 13C-NMR (67.5 MHz, CDCl3): δ = 180.3 (q, 2JCF = 35.2 Hz), 156.1, 131.2, 130.5, 123.0, 122.8,
116.6 (q, 1JCF = 291.6 Hz), 116.2. HRMS (ESI): m/z calculated for C8H5F3O2 + H+ [M + H+]: 191.0320.
Found: 191.0316.
Methyl (S)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoate (S)-33. To 2,2,2-trifluoro-1-(4-hydro
xyphenyl)ethanone 31 (1.175 g, 7.25 mmol) in dry CH2Cl2 (30 mL), D-(+)-lactate
4 (1.132 g, 10.9 mmol)
and PPh3 (2.282 g, 8.70 mmol) was added at 0 ◦C. After the reaction mixture was stirred for 10 min
at 0 ◦C, DEAD (1.891 g, 10.9 mmol) was slowly added at same temperature. The reaction mixture
was stirred overnight at room temperature and partitioned between water and CH2Cl2. The organic

Molecules 2020, 25, 2790
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layer was washed with brine, dried over MgSO4, filtered and concentrated. The residue was purified
by column chromatography (ethyl acetate/n-hexane, 1:9) to give (S)-33 (1.560 g, 78%). [ 48 (c
1, CHCl3). 1H-NMR (270 MHz, CDCl3):
= 7.96 (d, J = 8.2 Hz, 2H), 6.88 (d, J = 8.2 Hz, 2H), 4.82
= 178.8 (q,
α
]
−
D
δ
(q, J = 6.8 Hz, 1H), 3.70 (s, 3H), 1.59 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
2JCF = 34.6 Hz), 171.4, 163.2, 132.7, 123.4, 116.8 (q, 1JCF = 291.4 Hz), 115.2, 72.5, 52.5, 18.3. HRMS (ESI):
m/z calculated for C12H11F3O4 + H+ [M + H+]: 277.0688. Found: 277.0674.
Methyl (R)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-33. The similar treatment of
2,2,2-trifluoro-1-(4-hydroxyphenyl)ethenone 31 (484 mg, 2.99 mmol) and methyl L-(
−
)-lactate
5
1
(466 mg, 4.48 mmol) as that just described gave (R)-33 (614 mg, 74%). [
α
]
+48 (c 1, CHCl3). H-NMR
D
(270 MHz, CDCl3):
δ
= 8.04 (d, J = 8.2 Hz, 2H), 6.97 (d, J = 8.2 Hz, 2H), 4.91 (q, J = 6.8 Hz, 1H), 3.78
2
(s, 3H), 1.68 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 178.8 (q, JCF = 34.6 Hz), 171.4,
163.2, 132.7, 123.4, 116.8 (q, 1JCF = 291.4 Hz), 115.2, 72.5, 52.5, 18.3. HRMS (ESI): m/z calculated for
C12H11F3O4 + H+ [M + H+]: 277.0688. Found: 277.0660.
Methyl (S)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate (S)-34. The similar treatment of
2,2,2-trifluoro-1-(3-hydroxyphenyl)ethanone 32 (248 mg, 1.53 mmol) and methyl D-(
(248 mg, 2.30 mmol) as that just described gave (S)-34 (300 mg, 71%). [
(270 MHz, CDCl3):
−
)-lactate
45 (c 1, CHCl3). H-NMR
4
1
α
]
D
−
δ
= 7.69 (d, J = 7.8 Hz, 1H), 7.52 (s, 1H), 7.46 (t, J = 7.8 Hz, 1H), 7.23 (d, J = 7.8 Hz,
= 180.1
1H), 4.84 (q, J = 6.8 Hz, 1H), 3.78 (s, 3H), 1.66 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
(q, 2JCF = 35.2 Hz), 171.9, 157.9, 131.2, 130.3, 123.5, 123.0, 118.7, 116.6 (q, 1JCF = 291.1 Hz), 115.5, 72.7,
52.5, 18.4. HRMS (ESI): m/z calculated for C12H11F3O4 + H+ [M + H+]: 277.0688. Found: 277.0688.
Methyl (R)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-34. The similar treatment of
2,2,2-trifluoro-1-(3-hydroxyphenyl)ethanone 32 (655 mg, 4.04 mmol) and methyl L-(
(631 mg, 6.06 mmol) as that just described gave (R)-34 (835 mg, 75%). [
(270 MHz, CDCl3):
−
)-Lactate
+45 (c 1, CHCl3). H-NMR
5
1
α
]
D
δ
= 7.69 (d, J = 7.8 Hz, 1H), 7.53 (s, 1H), 7.46 (t, J = 7.8 Hz, 1H), 7.24 (d, J = 7.8 Hz,
1H), 4.85 (q, J = 6.8 Hz, 1H), 3.78 (s, 3H), 1.67 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3): δ = 180.0
(q, 2JCF = 35.2 Hz), 171.8, 157.9, 131.1, 130.3, 123.4, 122.9, 118.7, 116.5 (q, 2JCF = 291.1 Hz), 115.4, 72.7,
52.4, 18.3. HRMS (ESI): m/z calculated for C12H11F3O4 + H+ [M + H+]: 277.0688. Found: 277.0685.
(S)-2-(4-(2,2,2-Trifluoroacetyl)phenoxy)propanoic acid ((S)-35). Methyl (S)-2-(4-(2,2,2-trifluoroa
cetyl)phenoxy)propanoate (S)-33 (402 mg, 1.46 mmol) was dissolved in MeOH (18 mL) and H2O
(2 mL), and then K2CO3 (605 mg, 4.37 mmol) was added. After the reaction mixture was stirred at
reflux for 2 h, cooled to room temperature and then partitioned between ethyl acetate and water.
The water layer was acidified by 1 M HCl and extracted by ethyl acetate. The organic layer was washed
by H2O and brine, and dried over MgSO4, filtrated and concentrated to give (S)-35 (400 mg, quant).
1
[
α
]
−
31 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 9.05 (1H, s), 7.97 (d, J = 8.9 Hz, 2H), 6.91 (d,
= 178.9
D
J = 8.9 Hz, 2H), 4.85 (q, J = 6.8 Hz, 1H), 1.65 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
(q, 2JCF = 35.2 Hz), 176.7, 162.9, 132.8, 123.7, 116.8 (q, 1JCF = 291.6 Hz), 115.2, 72.0, 18.2. HRMS (ESI):
m/z calculated for C11H9F3O4 + H+ [M + H+]: 263.0531. Found: 263.0543.
(R)-2-(4-(2,2,2-Trifluoroacetyl)phenoxy)propanoic acid ((R)-35). The similar treatment of methyl
(R)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-33 (476 mg, 1.72 mmol) as that just described
1
gave (R)-35 (428 mg, 95%). [
α
]
+31 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.99 (d, J = 8.9 Hz,
D
2H), 6.92 (d, J = 8.9 Hz, 2H), 4.86 (q, J = 6.8 Hz, 1H), 1.66 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz,
CDCl3):
δ
= 178.9 (q, 2JCF = 34.6 Hz), 176.4, 162.9, 132.8, 123.8, 116.8 (q, 1JCF = 291.3 Hz), 115.2, 71.9,
18.2. HRMS (ESI): m/z calculated for C11H9F3O4 + H+ [M + H+]: 263.0531. Found: 263.0541.
(S)-2-(3-(2,2,2-Trifluoroacetyl)phenoxy)propanoic acid ((S)-36). The similar treatment of methyl
(S)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate (S)-34 (285 mg, 1.03 mmol) as that just described gave
1
(S)-36 (268 mg, 99%). [
α
]
−
28 (c 1, CHCl3). H-NMR (270 MHz, CDCl3): δ = 7.70 (d, J = 7.6 Hz, 1H)
,
,
D
7.56 (s, 1H), 7.47 (t, J = 8.1 Hz, 1H), 7.25 (d, J = 8.6 Hz, 1H), 4.88 (q, J = 6.8 Hz, 1H), 1.70 (d, J = 6.9 Hz
3H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 180.1 (q, 2JCF = 35.2 Hz), 177.4, 157.7, 131.2, 130.4, 123.7, 122.8,
116.5 (q, 1JCF = 291.3 Hz), 115.7, 72.2, 18.2. HRMS (ESI): m/z calculated for C11H9F3O4 + H+ [M + H+]:
263.0531. Found: 263.0543.

Molecules 2020, 25, 2790
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(R)-2-(3-(2,2,2-Trifluoroacetyl)phenoxy)propanoic acid ((R)-36). The similar treatment of methyl
(R)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-34 (288 mg, 1.04 mmol) as that just described
gave (R)-36 (265 mg, 97%). [
α
]
+28 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 7.59 (d,
D
J = 7.6 Hz, 1H), 7.46 (s, 1H), 7.36 (t, J = 8.1 Hz, 1H), 7.14 (d, J = 8.2 Hz, 1H), 4.78 (q, J = 6.8 Hz, 1H),
2
1.60 (d, J = 6.8 Hz, 3H)
.
13C-NMR (67.5 MHz, CDCl3):
δ
= 180.1 (q, JCF = 35.2 Hz), 177.3, 157.7,
131.1, 130.4, 123.6, 122.8, 116.5 (q, 1JCF = 291.6 Hz), 115.7, 72.2, 18.2. HRMS (ESI): m/z calculated for
C11H9F3O4 + H+ [M + H+]: 263.0531. Found: 263.0538.
tert-Butyl (S)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoate ((S)-37). To a solution of (S)-2-(4-
(2,2,2-trifluoroacetyl)phenoxy)propanoic acid 35 (138 mg, 0.53 mmol), potassium carbonate (1.816
g, 13.1 mmol) and tetrabutylammonium bromide (169 mg, 0.53 mmol) in N,N-dimethylacetamide
(2.6 mL), tert-butyl bromide (3.416 g, 24.9 mmol) was added dropwise at 0 ◦C. The reaction mixture
was stirred at 55 ◦C for 2.5 h. After cooling to room temperature, the mixture was poured into cold
water and extracted with ethyl acetate. The water layer was added 1 M HCl to make pH 1 and
extracted with ethyl acetate, washed with brine, dried, filtrated and concentrated to recover (S)-36
(21.8 mg, 16%). The organic layer was washed with H2O, brine, dried over MgSO4, filtrated and
evaporated. The residue was purified by column chromatography (ethyl acetate/n-hexane, 1:6) to give
1
(S)-37 (111 mg, 66%). [
α
]
−
38 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 8.04 (d, J = 8.9 Hz, 2H),
D
6.96 (d, J = 8.9 Hz, 2H), 4.75 (q, J = 6.8 Hz, 1H), 1.64 (d, J = 6.8 Hz, 3H), 1.45 (s, 9H). 13C-NMR (67.5 MHz,
CDCl3):
δ
= 178.9 (q, 2JCF = 35.2 Hz), 170.1, 163.5, 132.7, 123.3, 116.9 (q, 1JCF = 291.1 Hz), 115.2, 82.7,
73.0, 27.9, 18.2. HRMS (ESI): m/z calculated for C15H17F3O4 + H+ [M + H+]: 319.1157. Found: 319.1158.
tert-Butyl (R)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoate ((R)-37). The similar treatment of
(R)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoic acid (R)-35 (428 mg, 1.63 mmol) as that just described
1
gave (R)-37 (363 mg, 70%). [
α
]
+38 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.96 (d, J = 8.9 Hz,
D
2H), 6.88 (d, J = 8.9 Hz, 2H), 4.67 (q, J = 6.8 Hz, 1H), 1.55 (d, J = 6.8 Hz, 3H), 1.36 (s, 9H). 13C-NMR
(67.5 MHz, CDCl3):
δ
= 178.8 (q, 2JCF = 34.6 Hz), 170.1, 163.5, 132.6, 123.2, 116.8 (q, 1JCF = 291.1 Hz),
115.2, 82.6, 73.0, 27.8, 18.2. HRMS (ESI): m/z calculated for C15H17F3O4 + H+ [M + H+]: 319.1157.
Found: 319.1147.
tert-Butyl (S)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate ((S)-38). The similar treatment of
(S)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoic acid (S)-36 (310 mg, 1.18 mmol) as that just described
gave (S)-36 (149 mg, 48%) and (S)-38 (141 mg, 38%). [
CDCl3): = 7.67 (d, J = 7.8 Hz, 1H), 7.51 (s, 1H), 7.45 (t, J = 7.8 Hz, 1H), 7.25 (d, J = 7.8 Hz, 1H), 4.69
(q, J = 6.8 Hz, 1H), 1.62 (d, J = 6.8 Hz, 3H), 1.45 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
= 180.2 (q,
α
]
−
53 (c 1, CHCl3). 1H-NMR (270 MHz,
D
δ
δ
2JCF = 34.6 Hz), 170.6, 158.2, 131.0, 130.2, 123.3, 123.2, 116.6 (q, 1JCF = 291.1 Hz), 115.0, 82.5, 73.0, 27.8,
18.3. HRMS (ESI): m/z calculated for C15H17F3O4 + H+ [M + H+]: 319.1157. Found: 319.1159.
tert-Butyl (R)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate((R)-38). The similar treatment of
(R)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoic acid (R)-36 (344 mg, 1.31 mmol) as that just described
gave (R)-36 (167 mg, 48%) and (R)-38 (153 mg, 37%). [
CDCl3): = 7.68 (d, J = 7.8 Hz, 1H), 7.51 (s, 1H), 7.45 (t, J = 7.8 Hz, 1H), 7.24 (d, J = 7.8 Hz, 1H), 4.69
(q, J = 6.8 Hz, 1H), 1.62 (d, J = 6.8 Hz, 3H), 1.45 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
= 180.1 (q,
α]
+53 (c 1, CHCl3). 1H-NMR (270 MHz,
D
δ
δ
2JCF = 35.2 Hz), 170.6, 158.2, 131.0, 130.2, 123.3, 123.2, 116.6 (q, 1JCF = 291.1 Hz), 115.0, 82.5, 73.0, 27.8,
18.3. HRMS (ESI): m/z calculated for C15H17F3O4 + H+ [M + H+]: 319.1157. Found: 319.1183.
2-(1,3-Dithian-2-yl)phenol 40. Salicylaldehyde 39 (0.62 g, 5.06 mmol) and iodine (130 mg,
0.51 mmol) were dissolved in CH2Cl2 (25 mL) and then 1,3-propanedithiol (0.65 g, 6.00 mmol) was
added. After the reaction mixture was stirred at room temperature for 1 h, then quenched aqueous
sodium thiosulfate (0.5 M, 10 mL). The mixture was extracted with CH2Cl2, washed with brine, dried
1
over MgSO4, filtrated and concentrated to give 2-(1,3-dithian-2-yl)phenol 40 (1.02 g, 95%). H-NMR
(270 MHz, CDCl3):
2H), 6.33 (s, 1H), 5.40 (s, 1H), 3.07 (td, J = 13.6, 3.0 Hz, 2H), 2.91 (dt, J = 14.2, 3.6 Hz, 2H), 2.26–2.13 (m,
1H), 2.00–1.87 (m, 1H). 13C-NMR (67.5 MHz, CDCl3):
= 154.5, 130.1, 129.1, 123.5, 120.8, 117.3, 47.4,
31.6, 24.8. HRMS (ESI): m/z calculated for C10H12O2S2 + H+ [M + H+]: 213.0408. Found: 213.0383.
δ = 7.29 (dd, J = 7.9, 1.6 Hz, 1H), 7.21 (td, J = 7.7, 1.6 Hz, 1H), 6.88 (dq, J = 7.4, 2.0 Hz,
δ

Molecules 2020, 25, 2790
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Methyl (S)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoate ((S)-41). 2-(1,3-Dithian-2-yl)phenol 40
(1.27 g) phenol, methyl D-(+)-lactate
4 (0.94 g, 8.99 mmol) and PPh3 (1.90 g, 7.22 mmol) were dissolved
in dry CH2Cl2 (30 mL). After stirring for 10 min at 0 ◦C, DEAD (1.57 g, 9.02 mmol) was slowly added.
The reaction mixture was stirred overnight at room temperature, and then partitioned between water
and CH2Cl2. The organic layer was washed with brine, dried over MgSO4, filtered and concentrated.
The residue was purified by column chromatography (ethyl acetate/n-hexane, 1:9) to give (S)-41 (1.48 g,
1
98%). [
α
]
D +31 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.60 (d, J = 7.6 Hz, 1H), 7.19 (t, J = 7.6 Hz,
1H), 7.00 (t, J = 7.6 Hz, 1H), 6.75 (d, J = 7.6 Hz, 1H), 5.76 (s, 1H), 4.78 (q, J = 6.8 Hz, 1H), 3.75 (s, 3H), 3.11
(m, 2H), 2.88 (m, 2H), 2.16 (m, 1H), 1.95 (m, 1H), 1.67 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 172.3, 153.8, 129.4, 129.2, 128.6, 122.2, 113.4, 73.9, 52.2, 43.8, 32.3, 32.2, 25.3, 18.5. HRMS (ESI): m/z
calculated for C14H18O3S2 + Na+ [M + Na+]: 321.0595. Found: 321.0597.
Methyl (R)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoate ((R)-41). 2-(1,3-Dithian-2-yl)phenol 40
1
(1.27 g) as that just described gave (R)-41 (1.47 g, 98%). [
CDCl3):
5.76 (s, 1H), 4.78 (q, J = 6.8 Hz, 1H), 3.75 (s, 3H), 3.11 (m, 2H), 2.90 (m, 2H), 2.16 (m, 1H), 1.95 (m, 1H),
α
]
−
31 (c 1, CHCl3). H-NMR (270 MHz,
D
δ
= 7.60 (d, J = 7.6 Hz, 1H), 7.19 (t, J = 7.6 Hz, 1H), 7.00 (t, J = 7.6 Hz, 1H), 6.75 (d, J = 7.6 Hz, 1H),
1.67 (d, J = 6.9 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ = 172.3, 153.8, 129.4, 129.2, 128.7, 122.3, 113.4,
74.0, 52.2, 43.8, 32.3, 32.2, 25.3, 18.6. HRMS (ESI): m/z calculated for C14H18O3S2 + Na+ [M + Na+]:
321.0595. Found: 321.0598.
(S)-2-(2-(1,3-Dithian-2-yl)phenoxy)propanoic acid (S)-42. Methyl (S)-2-(2-(1,3-dithian-2-yl)phen
oxy)propanoate (S)-41 (1.51 g, 5.06 mmol) was dissolved in MeOH (30 mL) and H2O (3.3 mL), and
then K2CO3 (700 mg, 5.06 mmol) was added. After the reaction mixture was stirred at reflux for 2 h,
cooled to room temperature and then partitioned between ethyl acetate and water. The water layer
was acidified by 1 M HCl aq and extracted by ethyl acetate. The organic layer was washed by H2O
and brine, and dried over MgSO4, filtrated and concentrated to give (S)-42 (1.63 g, quant). [α]D +9 (c 1
CHCl3). 1H-NMR (270 MHz, CDCl3):
= 7.55 (d, J = 7.6 Hz, 1H), 7.26 (t, J = 7.6 Hz, 1H), 7.03 (t,
J = 7.6 Hz, 1H), 6.82 (d, J = 7.6 Hz, 1H), 5.62 (s, 1H), 4.88 (q, J = 6.8 Hz, 1H), 3.12 (m, 2H), 2.92 (m,
2H), 2.19 (m, 1H), 1.96 (m, 1H), 1.71 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
= 174.9,
,
δ
δ
153.3, 129.6, 129.5, 128.1, 122.6, 112.8, 73.0, 45.4, 32.2, 32.1, 25.3, 18.0. HRMS (ESI): m/z calculated for
C13H16O3S2 + H+ [M + H+]: 285.0619. Found: 285.0591.
(R)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoic acid (R)-42. The similar treatment of methyl
(R)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoate (R)-41 (1.56 g, 5.22 mmol) as that just described gave
1
(S)-42 (1.69 g, quant). [
α
]
D
−
9 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.56 (d, J = 7.6 Hz, 1H),
7.24 (t, J = 7.6 Hz, 1H), 7.02 (t, J = 7.6 Hz, 1H), 6.81 (d, J = 7.6 Hz, 1H), 5.65 (s, 1H), 4.85 (q, J = 6.8 Hz,
1H), 3.11 (m, 2H), 2.90 (m, 2H), 2.18 (m, 1H), 1.95 (m, 1H), 1.71 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz,
CDCl3):
δ = 175.8, 153.3, 129.5, 129.5, 128.2, 122.5, 112.9, 73.1, 45.0, 32.2, 32.1, 25.2, 18.1. HRMS (ESI):
m/z calculated for C13H16O3S2 + H+ [M + H+]: 285.0619. Found: 285.0608.
tert-Butyl (S)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoate (S)-43.
To
a
solution of
(S)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoic acid (1.63 g, 5.72 mmol) in N,N-dimethylacetamide
(29 mL) in the presence of potassium carbonate (19.8 g, 143 mmol) and tetrabutylammonium bromide
(1.85 g, 5.73 mmol) at 0 ◦C, tert-butyl bromide (37.6 g, 274 mmol) was added dropwise and the reaction
mixture was stirred at 55 ◦C for 2.5 h. After cooling to room temperature, the mixture was added into
cold water and extracted with ethyl acetate. The organic layer was washed with H2O, brine, dried
over MgSO4, filtrated and evaporated. The residue was purified by column chromatography (ethyl
1
acetate/n-hexane, 1:6) to give (S)-43 (1.61 g, 83%). [
α
]
+25 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
D
δ = 7.59 (d, J = 7.8 Hz, 1H), 7.18 (t, J = 7.8 Hz, 1H), 6.97 (t, J = 7.8 Hz, 1H), 6.74 (d, J = 7.8 Hz, 1H), 5.75 (s,
1H), 4.64 (q, J = 6.8 Hz, 1H), 3.11 (m, 2H), 2.88 (m, 2H), 2.16 (m, 1H), 1.93 (m, 1H), 1.63 (d, J = 6.8Hz, 3H),
1.43 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ = 171.0, 153.9, 129.3, 129.0, 128.3, 121.8, 112.8, 81.8, 73.9,
43.8, 32.3, 32.2, 27.9, 25.4, 18.4. HRMS (ESI): m/z calculated for C17H24O3S2 + H+ [M + H+]: 341.1245.
Found: 341.1237.

Molecules 2020, 25, 2790
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tert-Butyl (R)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoate (R)-43. The similar treatment of
(R)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoic acid 42 (1.69 g, 5.93 mmol) as that just described gave
1
(R)-43 (1.65 g, 82%). [
α
]
−
25 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.59 (d, J = 7.8 Hz, 1H),
D
7.18 (t, J = 7.8 Hz, 1H), 6.97 (t, J = 7.8 Hz, 1H), 6.73 (d, J = 7.8 Hz, 1H), 5.75 (s, 1H), 4.64 (q, J = 6.8 Hz,
1H), 3.11 (m, 2H), 2.88 (m, 2H), 2.16 (m, 1H), 1.95 (m, 1H), 1.63 (d, J = 6.8 Hz, 3H), 1.43 (s, 9H). 13C-NMR
(67.5 MHz, CDCl3):
δ = 171.0, 153.9, 129.3, 129.0, 128.3, 121.8, 112.8, 81.8, 73.9, 43.8, 32.4, 32.2, 27.9, 25.4,
18.4. HRMS (ESI): m/z calculated for C17H24O3S2 + H+ [M + H+]: 341.1245. Found: 341.1239.
tert-Butyl (S)-2-(2-formylphenoxy)propanoate (S)-44. tert-Butyl (S)-2-(2-(1,3-dithian-2-yl)pheno
xy)propanoate (S)-43 (94.3 mg, 0.28 mmol) and sodium hydrogen carbonate (465 mg, 5.54 mmol) were
dissolved in acetonitrile (10 mL) and water (2 mL), and then iodomethane (392 mg, 2.8 mmol)was
added. After the reaction mixture was stirred at room temperature for 24 h, iodomethane (196 mg,
1.4 mmol) was added. After stirred at room temperature for 24 h, the reaction mixture extracted with
ethyl acetate. The organic layer was washed with brine, dried over MgSO4, filtrated and concentrated.
The residue was purified by column chromatography (ethyl acetate/n-hexane, 1:6) to give (S)-44
1
(52.3 mg, 78%). [
α
]
D +14 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 10.57 (s, 1H), 7.85 (d, J = 7.9 Hz,
1H), 7.49 (t, J = 7.9 Hz, 1H), 7.04 (t, J = 7.9 Hz, 1H), 6.85 (d, J = 7.9 Hz, 1H), 4.77 (q, J = 6.8 Hz, 1H), 1.66
(d, J = 6.8 Hz, 3H), 1.42 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ = 189.7, 170.4, 160.2, 135.5, 128.2, 125.4,
121.4, 113.2, 82.3, 73.5, 27.8, 18.2. HRMS (ESI): m/z calculated for C14H18O4 + H+ [M + H+]: 251.1283.
Found: 251.1312.
tert-Butyl (R)-2-(2-formylphenoxy)propanoate (R)-44. The similar treatment of tert-butyl
(R)-2-(2-(1,3-dithian-2-yl)phenoxy)propanoate (R)-43 (156 mg, 0.46 mmol) as that just described
gave (R)-44 (90.4 mg, 79%). [
7.84 (d, J = 7.6 Hz, 1H), 7.50 (t, J = 7.6 Hz, 1H), 7.04 (t, J = 7.6 Hz, 1H), 6.85 (d, J = 7.6 Hz, 1H), 4.78
(q, J = 6.8 Hz, 1H), 1.66 (d, J = 6.8 Hz, 3H), 1.42 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
= 189.7,
α
]
−
14 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 10.58 (s, 1H),
D
δ
170.4, 160.2, 135.5, 128.2, 125.4, 121.4, 113.2, 82.3, 73.5, 27.8, 18.2. HRMS (ESI): m/z calculated for
C14H18O4 + H+ [M + H+]: 251.1283. Found: 251.1292.
tert-Butyl (S)-2-(2-(2,2,2-trifluoroacetyl)phenoxy)propanoate (S)-45. To the solution of tert-butyl
(S)-2-(2-formylphenoxy)propanoate (S)-44 (591 mg, 2.04 mmol) in dimethylacetamide (7.9 mL),
(trifluoromethyl)trimetylsilane (579 mg, 4.07 mmol) and potassium carbonate (16.3 mg, 0.118 mmol)
were added. The reaction mixture was and stirred at room temperature for 4 h and treated with 1 M HCl
(1 mL) at room temperature for 4 h, then extracted with ethyl acetate. The organic layer was washed
with brine twice, dried over MgSO4, filtrated and concentrated to afford crude material. To crude
phenylethanol derivative (784 mg) was dissolved in CH2Cl2 (13 mL), Dess-Martin periodinane (1.096 g,
2.58 mmol) was added at room temperature. The reaction mixture was stirred at room temperature
for 3 h, then washed with water and brine. The organic layer was dried over MgSO4, filtrated and
concentrated. The residue was subjected to column chromatography (hexane/AcOEt, 8:1) to give
(S)-45 (636 mg, 85%). [
1H), 7.41 (t, J = 7.6 Hz, 1H), 6.95 (t, J = 7.6 Hz, 1H), 6.71 (d, J = 7.6 Hz, 1H), 4.61 (q, J = 6.8 Hz, 1H),
α] δ = 7.54 (d, J = 7.6 Hz,
+25 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
D
1.51 (d, J = 6.8 Hz, 3H), 1.30 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 183.6 (q, 2JCF = 37.4 Hz), 170.2,
157.5, 135.3, 131.5, 122.6, 121.2, 116.1 (q, 1JCF = 290.5 Hz), 112.8, 82.4, 73.7, 27.8, 17.8. HRMS (ESI): m/z
calculated for C15H17F3O4 + H+ [M + H+]: 319.1157. Found: 319.1171.
tert-Butyl (R)-2-(2-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-45. The similar treatment of
tert-butyl (R)-2-(2-formylphenoxy)propanoate (R)-44 (577 mg, 2.30 mmol) as that just described gave
(R)-45 (651 mg, 89%). [
α
]
−
25 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 7.65 (d, J = 7.6 Hz,
D
1H), 7.53 (t, J = 7.6 Hz, 1H), 7.06 (t, J = 7.6 Hz, 1H), 6.83 (d, J = 7.6 Hz, 1H), 4.72 (q, J = 6.8 Hz, 1H),
1.62 (d, J = 6.8 Hz, 3H), 1.41 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 183.6 (q, 2JCF = 37.4 Hz), 170.2,
157.5, 135.3, 131.6, 122.6, 121.2, 116.1 (q, 1JCF = 290.5 Hz), 112.8, 82.4, 73.7, 27.8, 17.8. HRMS (ESI): m/z
calculated for C15H17F3O4 + H+ [M + H+]: 319.1157. Found: 319.1141.
tert-Butyl (S)-2-(4-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)propanoate ((S)-46). A solution
of tert-butyl (S)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoate (S)-37 (252 mg, 0.79 mmol) and

Molecules 2020, 25, 2790
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hydroxylamine hydrochloride (60.7 mg, 0.87 mmol) in ethanol (0.44 mL) and dry pyridine (0.79 mL)
was heated at 60 ◦C for 8 h. The reaction mixture was partitioned between water and ether, and the
organic layer was washed with 1 M HCl, saturated NaHCO3 and brine. The organic layer was dried
over MgSO4, filtrated and concentrated. The residue was purified by column chromatography (ethyl
acetate/n-hexane, 1:6) to give (S)-46 (275 mg, quant). The product was mixture of syn- and anti- isomers.
1
[
α
]
−
38 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 8.89 and 8.75 (s, 1H), 7.44 and 7.34 (d
2, J = 6.8 Hz, 1H), 1.53 (d,
= 171.0, 159.3, 146.9 (q, 2JCF = 32.4 Hz),
×
2,
D
J = 8.9 Hz, 2H), 6.86 and 6.81 (d
J = 6.8 Hz, 3H), 1.37 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
×
2, J = 8.9 Hz, 2H), 4.60 and 4.59 (q
×
δ
1
130.5, 120.8 (q, JCF = 274.9 Hz), 118.6, 114.9, 82.4, 72.9, 27.9, 18.3. HRMS (ESI): m/z calculated for
C15H18F3NO4 + H+ [M + H+]: 334.1266. Found: 334.1256.
tert-Butyl (R)-2-(4-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)propanoate ((R)-46). The similar
treatment of tert-butyl (R)-2-(4-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-37 (459 mg, 1.44 mmol)
1
as that just described gave (R)-46 (490 mg, quant). [
= 8.36 and 8.19 (s, 1H), 7.50 and 7.42 (d
and 4.66 (q
α
]
D
+38 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
×
2, J = 7.8 Hz, 2H), 6.93 and 6.88 (d
×
2, J = 8.9 Hz, 2H), 4.67
×
2, J = 6.8 Hz, 1H), 1.60 (d, J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ = 171.0, 159.3, 146.9 (q, 2JCF = 32.4 Hz), 130.5, 120.8 (q, 1JCF = 274.9 Hz), 118.6, 114.9, 82.4, 72.9, 27.9,
18.3. HRMS (ESI): m/z calculated for C15H18F3NO4 + H+ [M + H+]: 334.1266. Found: 334.1236.
tert-Butyl (S)-2-(3-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)propanoate ((S)-47). The similar
treatment of tert-butyl (S)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate (S)-38 (81.7 mg, 0.26 mmol) as
1
that just described gave (S)-47 (85.7 mg, quant). [
δ = 7.36 and 7.30 t
1.60 and 1.59 (d 2, J = 6.8 Hz, 3H), 1.43 and 1.42 (s
α
]
−
40 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
D
×
2, J = 7.8 Hz, 1H), 7.09 (d, J = 7.8 Hz, 1H), 6.97 (m, 2H), 4.66 (q, J = 6.8 Hz, 1H),
×
×
2, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 171.3,
157.6, 147.3 (q, 2JCF = 32.4 Hz), 129.7 and 129.6, 127.2, 121.5, 120.6 (q, 1JCF = 274.3 Hz), 117.4 and 117.0,
115.4 and 115.2, 82.5, 73.1, 27.8, 18.4. HRMS (ESI): m/z calculated for C15H18F3NO4 + H+ [M + H+]:
334.1266. Found: 334.1265.
tert-Butyl (R)-2-(3-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)propanoate ((R)-47). The similar
treatment of tert-butyl (R)-2-(3-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-38 (97.2 mg, 0.31 mmol) as
1
that just described gave (R)-47 (86.6 mg, 85%). [
δ = 7.37 and 7.30 (t
α
]
+40 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
D
×
2, J = 7.8 Hz, 2H), 7.08 (d, J = 7.8 Hz, 1H), 6.97 (m, 2H), 4.65 (q, J = 6.8 Hz, 1H),
1.60 (d, J = 6.8 Hz, 3H), 1.43 and 1.42 (s × 2, 9H). 13C-NMR (67.5 MHz, CDCl3): δ = 171.1, 157.6, 147.6
(q, 2JCF = 32.4 Hz), 129.7 and 129.5, 127.1, 121.4, 120.5 (q, 1JCF = 274.9 Hz), 117.4 and 117.1, 115.3 and
115.1, 82.3, 73.1, 27.8, 18.4. HRMS (ESI): m/z calculated for C15H18F3NO4 + H+ [M + H+]: 334.1266.
Found: 334.1257.
tert-Butyl (S)-2-(2-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)propanoate ((S)-48). The similar
treatment of tert-butyl (S)-2-(2-(2,2,2-trifluoroacetyl)phenoxy)propanoate (S)-45 (309 mg, 0.97 mmol) as
1
that just described gave (S)-48 (331 mg, quant). [
δ = 7.37 and 7.36 (t 2, J = 7.6 Hz, 1H), 7.27 and 7.21 (d
1H), 6.80 and 6.75 (d 2, J = 7.6 Hz, 1H), 4.62 (q, J = 6.8 Hz, 1H), 1.57 and 1.54 (d
1.41 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
= 171.2 and 171.0, 156.5, 155.1, 147.6 and 146.7 (q
α
]
+8 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
D
×
×
2, J = 7.6 Hz, 1H), 7.03 and 6.99 (t
2, J = 6.8 Hz, 3H),
2,
×
2, J = 7.6 Hz,
×
×
δ
×
2JCF = 33.5 Hz), 131.6, 131.0, 129.8, 121.0, 117.9 (q, 1JCF = 287.2 Hz), 116.3, 112.2 and 111.7, 82.3 and
82.2, 73.5 and 73.4, 27.8, 18.2 and 18.0. HRMS (ESI): m/z calculated for C15H18F3NO4 + H+ [M + H+]:
334.1266. Found: 334.1246.
tert-Butyl (R)-2-(2-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)propanoate ((R)-48). The similar
treatment of tert-butyl (R)-2-(2-(2,2,2-trifluoroacetyl)phenoxy)propanoate (R)-45 (291 mg, 0.92 mmol)
as that just described gave (R)-48 (299 mg, 98%).
[
α
]
−
8 (c 1, CHCl3). 1H-NMR (270 MHz,
D
CDCl3): δ = 7.37 (m, 1H), 7.27 and 7.21 (d, J = 7.6 Hz, 1H), 7.03 and 6.98 (t, J = 7.6 Hz, 1H), 6.80 and
6.74 (d, J = 7.6 Hz, 1H), 4.62 (q, J = 6.8 Hz, 1H), 1.57 and 1.54 (d, J = 6.8 Hz, 3H), 1.41 (s, 9H). 13C-NMR
(67.5 MHz, CDCl3):
131.0, 129.8, 121.0, 120.5 and 118.2 (q
δ
= 171.2 and 171.1, 156.5, 155.1, 147.5 and 146.5 (q
×
2, 2JCF = 34.1 Hz), 131.6,
×
2, 1JCF = 287.2 Hz), 116.3, 112.2 and 111.7, 82.3 and 82.2, 73.5

Molecules 2020, 25, 2790
19 of 25
and 73.4, 27.8, 18.1 and 18.0. HRMS (ESI): m/z calculated for C15H18F3NO4 + H+ [M + H+]: 334.1266.
Found: 334.1261.
tert-Butyl (S)-2-(4-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)propanoate ((S)-49). tert-Butyl
(S)-2-(4-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)propanoate (S)-46 (268 mg, 0.80 mmol),
triethylamine (203 mg, 2.01 mmol) and DMAP (4.9 mg, 0.040 mmol) were suspended in CH2Cl2
(1.5 mL) at 0 ◦C. p-Toluenesulfonyl chloride (168 mg, 0.88 mmol) was added at 0 ◦C. The reaction
mixture was stirred at room temperature for 45 min, then washed with water. The organic layer was
dried over MgSO4, filtrated and concentrated to give (S)-49 (418 mg, quant). The product was mixture
1
of syn- and anti- isomers. [
α
]
−
20 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.88 (d, J = 8.2 Hz,
2,
= 170.5 and
D
2H), 7.45–7.35 (m, 4H), 6.92 and 6.87 (d, J = 8.2 Hz, 2H), 4.68 (q, J = 6.8 Hz, 1H), 2.46 and 2.45 (s
×
3H), 1.61 and 1.60 (d
×
2, J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ
170.4, 160.6 and 160.2, 152.9 (q, 2JCF = 27.9 Hz), 146.0 and 145.9, 131.4 and 131.1, 130.5, 129.8, 129.1,
129.0, 128.9, 120.3, 119.7 and 117.4 (q, 1JCF = 276.0 Hz), 116.9, 115.0, 82.3, 72.8 and 72.7, 27.8 and 27.7,
21.6, 18.2. HRMS (ESI): m/z calculated for C22H24F3NO6S + H+ [M + H+]: 488.1355. Found: 488.1372.
tert-Butyl (R)-2-(4-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)propanoate ((R)-49). The similar
treatment of tert-butyl (R)-2-(4-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)-propanoate (R)-46 (331 mg,
1
0.99 mmol) as that just described gave (R)-49 (473 mg, 98%). [
CDCl3):
(s, 3H), 1.60 (d, J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
α
]
D +20 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 7.89 (d, J = 7.8 Hz, 2H), 7.38 (m, 4H), 6.87 (d, J = 7.8 Hz, 2H), 4.65 (q, J = 6.8 Hz, 1H), 2.46
= 170.5 and 170.4, 160.6
and 160.2, 153.2 (q, 2JCF = 29.9 Hz), 146.0 and 145.9, 131.4 and 131.1, 130.5, 129.8, 129.1, 128.9, 120.3,
118.6 (q, 1JCF = 283.8 Hz), 116.9, 115.0, 82.3, 72.8 and 72.7, 27.7 and 27.8, 21.6, 18.2. HRMS (ESI): m/z
calculated for C22H24F3NO6S + H+ [M + H+]: 488.1355. Found: 488.1380.
δ
tert-Butyl(S)-2-(3-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)propanoate((S)-50). The similar
treatment of tert-butyl (S)-2-(3-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)-propanoate (S)-47 (277 mg,
1
0.83 mmol) as that just described gave (S)-50 (431 mg, quant). [
CDCl3):
(s, 1H), 4.62 (q, J = 6.8 Hz, 1H), 2.48 (s, 3H), 1.60 (d, J = 6.8 Hz, 3H), 1.42 (s, 9H). 13C-NMR (67.5 MHz,
CDCl3):
= 170.7, 157.8 and 157.7, 153.6 (q, 2JCF = 32.4 Hz), 146.1 and 146.0, 131.5 and 131.2, 130.0, 129.9
α
]
−
34 (c 1, CHCl3). H-NMR (270 MHz,
D
δ
= 7.88 (d, J = 8.6 Hz, 2H), 7.35 (m, 3H), 7.00 (d, J = 7.8 Hz, 2H), 6.97 (d, J = 7.8 Hz, 2H), 6.85
δ
and 129.8, 129.3 and 129.1, 128.8, 125.6, 121.8 and 121.3, 119.5 (q, 1JCF = 274.3 Hz), 118.4 and 118.2, 115.4
and 114.9, 82.3, 73.0, 27.8, 21.7, 18.3. HRMS (ESI): m/z calculated for C22H24F3NO6S + H+ [M + H+]
488.1355. Found: 488.1330.
:
tert-Butyl (R)-2-(3-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)propanoate ((R)-50). The similar
treatment of tert-butyl (R)-2-(3-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)-propanoate (R)-47 (348 mg,
1
1.04 mmol) as that just described gave (R)-50 (471 mg, 93%). [
α
]
D +34 (c 1, CHCl3). H-NMR (270 MHz,
CDCl3):
δ
= 7.89 (d, J = 8.2 Hz, 2H), 7.35 (m, 3H), 7.02 (m, 2H), 6.93 (s, 1H), 4.61 (q, J = 6.7 Hz, 1H),
2.46 (s, 3H), 1.59 (d, J = 6.6 Hz, 3H), 1.42 (s, 9H). 13C-NMR (67.5 MHz, CDCl3): δ = 170.7, 157.8 and
157.7, 153.7 (q, 2JCF = 33.5 Hz), 146.1 and 146.0, 131.5 and 131.2, 130.0, 129.9 and 129.8, 129.3 and 129.1,
127.8, 125.6, 121.8 and 121.3, 119.5 (q, 1JCF = 280.5 Hz), 118.4 and 118.2, 115.4 and 114.9, 82.3, 73.1 and
73.0, 27.8, 21.8, 18.3. HRMS (ESI): m/z calculated for C22H24F3NO6S + H+ [M + H+]: 488.1355. Found:
488.1330.
tert-Butyl(S)-2-(2-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)propanoate((S)-51). The similar
treatment of tert-butyl (S)-2-(2-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)-propanoate (S)-48 (300 mg,
1
0.90 mmol) as that just described gave (S)-51 (412 mg, 94%). [
CDCl3):
6.72 (d, J = 7.6 Hz, 1H), 4.56 (q, J = 6.8 Hz, 1H), 2.45 (s, 3H), 1.47 (d, J = 6.8 Hz, 3H), 1.39 (s, 9H).
α
]D +24 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 7.88 (d, J = 8.2 Hz, 2H), 7.39 (m, 3H), 7.12 (d, J = 7.6 Hz, 1H), 6.97 (t, J = 7.6 Hz, 1H),
13C-NMR (67.5 MHz, CDCl3):
δ
= 170.3, 156.6, 155.3 (q, 2JCF = 34.6 Hz), 145.7, 132.9, 132.4, 131.7, 131.1,
129.8, 129.0, 121.1, 117.8, 116.8 (q, 1JCF = 283.2 Hz), 111.8, 82.2, 73.6, 27.7, 21.7, 17.8. HRMS (ESI): m/z
calculated for C22H24F3NO6S + H+ [M + H+]: 488.1355. Found: 488.1339.
tert-Butyl (R)-2-(2-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)propanoate ((R)-51). The similar
treatment of tert-butyl (R)-2-(2-(2,2,2-trifluoro-1-(hydroxyimino)ethyl)phenoxy)-propanoate (R)-48 (254 mg,

Molecules 2020, 25, 2790
20 of 25
0.76 mmol) as that just described gave (R)-51 (373 mg, quant). [
α
]
−
24 (c 1, CHCl3). 1H-NMR
D
(270 MHz, CDCl3):
δ = 7.88 (d, J = 8.2 Hz, 2H), 7.39 (m, 3H), 7.12 (d, J = 7.6 Hz, 1H), 6.97 (t, J = 7.6 Hz,
1H), 6.72 (d, J = 7.6 Hz, 1H), 4.55 (q, J = 6.8 Hz, 1H), 2.46 (s, 3H), 1.47 (d, J = 6.8 Hz, 3H), 1.39 (s, 9H).
13C-NMR (67.5 MHz, CDCl3):
δ
= 170.3, 156.6, 155.3 (q, 2JCF = 35.2 Hz), 145.7, 132.9, 132.4, 131.7, 131.1,
129.8, 129.1, 121.1, 117.8, 116.8 (q, 1JCF = 282.7 Hz), 111.8, 82.2, 73.6, 27.8, 21.7, 17.8. HRMS (ESI): m/z
calculated for C22H24F3NO6S + H+ [M + H+]: 488.1355. Found: 488.1362.
tert-Butyl (S)-2-(4-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)propanoate ((S)-52). To liquid
NH3 (10 mL) at
78 ◦C in a sealed tube, tert-butyl (S)-2-(2-(2,2,2-trifluoro-1-((tosyloxy)imino)-ethyl)phen
−
oxy)propanoate (S)-49 (336 mg, 0.69 mmol) in dry ether (3 mL) was added. The reaction mixture was
stirred at room temperature for 3 h. After evaporation of NH3 gas, the reaction mixture was partitioned
between ether and water. The organic layer was dried over MgSO4, filtrated and concentrated.
The residue was purified by column chromatography (ethyl acetate/n-hexane, 1:5) to give (S)-52
1
(200 mg, 88%). [
α
]
−
32 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.51 (d, J = 8.6 Hz, 2H), 6.88
D
(d, J = 8.6 Hz, 2H), 4.64 (q, J = 6.8 Hz, 1H), 2.76 (d, J = 8.6 Hz, 1H), 2.18 (d, J = 8.6 Hz, 1H), 1.59 (d,
J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ = 170.9, 159.0, 129.4, 124.3, 123.6 (q,
1JCF = 278.2 Hz), 115.1, 82.1, 72.8, 57.5 (q, 2JCF = 35.8 Hz), 27.9, 18.3. HRMS (ESI): m/z calculated for
C15H19F3N2O3 + H+ [M + H+]: 333.1426. Found: 333.1414.
tert-Butyl (R)-2-(4-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)propanoate ((R)-52). The similar
treatment of tert-butyl (R)-2-(4-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)-propanoate (R)-49 (433 mg,
1
0.89 mmol) as that just described gave (R)-52 (259 mg, 88%). [
α
]
D +32 (c 1, CHCl3). H-NMR (270 MHz,
CDCl3):
δ
= 7.52 (d, J = 8.6 Hz, 2H), 6.88 (d, J = 8.6 Hz, 2H), 4.64 (q, J = 6.8 Hz, 1H), 2.75 (s, 1H), 2.16
(s, 1H), 1.59 (d, J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ = 170.9, 159.0, 129.5,
124.3, 123.6 (q, 1JCF = 277.7 Hz), 115.1, 82.2, 72.8, 57.6 (q, 2JCF = 35.2 Hz), 27.9, 18.3. HRMS (ESI): m/z
calculated for C15H19F3N2O3 + H+ [M + H+]: 333.1426. Found: 333.1416.
tert-Butyl (S)-2-(3-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)propanoate ((S)-53). The similar
treatment of tert-butyl (S)-2-(3-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)-propanoate (S)-50
1
(431 mg, 0.88 mmol) as that just described gave (S)-53 (269 mg, 92%). [
(270 MHz, CDCl3):
1H), 4.64 (q, J = 6.8 Hz, 1H), 2.75 (s, 1H), 2.20 (s, 1H), 1.59 (d, J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR
α
]
−
38 (c 1, CHCl3). H-NMR
D
δ
= 7.32 (t, J = 7.6 Hz, 1H), 7.21 (d, J = 7.6 Hz, 1H), 7.12 (s, 1H), 6.94 (d, J = 7.6 Hz,
(67.5 MHz, CDCl3):
δ
= 170.9, 157.9, 133.1, 129.9, 123.5 (q, 1JCF = 278.2 Hz), 120.9, 116.9, 114.6, 82.2,
72.9, 57.9 (q, 2JCF = 35.8 Hz), 27.9, 18.3. HRMS (ESI): m/z calculated for C15H19F3N2O3 + H+ [M + H+]:
333.1426. Found: 333.1414.
tert-Butyl (R)-2-(3-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)propanoate ((R)-53). The similar
treatment of tert-butyl (R)-2-(3-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)-propanoate (R)-50 (471 mg,
1
0.97 mmol) as that just described gave (R)-53 (347 mg, quant). [
CDCl3):
J = 6.8 Hz, 1H), 2.74 (s, 1H), 2.18 (s, 1H), 1.59 (d, J = 6.8 Hz, 3H), 1.44 (s, 9H). 13C-NMR (67.5 MHz,
α
]D +38 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 7.32 (t, J = 7.6 Hz, 1H), 7.21 (d, J = 7.6 Hz, 1H), 7.12 (s, 1H), 6.94 (d, J = 7.6 Hz, 1H), 4.64 (q,
CDCl3):
δ
= 170.9, 157.9, 133.1, 129.9, 123.5 (q, 1JCF = 278.2 Hz), 120.9, 116.8, 114.6, 82.1, 72.8, 57.9 (q,
2JCF = 35.8 Hz), 27.9, 18.4. HRMS (ESI): m/z calculated for C15H19F3N2O3 + H+ [M + H+]: 333.1426.
Found: 333.1421.
tert-Butyl (S)-2-(2-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)propanoate ((S)-54). The similar
treatment of tert-butyl (S)-2-(2-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)-propanoate (S)-51
1
(354 mg, 0.73 mmol) as that just described gave (S)-54 (182 mg, 76%). [
(270 MHz, CDCl3):
(d, J = 7.6 Hz, 1H), 4.79 (q, J = 6.8 Hz, 1H), 1.63 (d, J = 6.8 Hz, 3H), 1.36 (s, 9H). 13C-NMR (67.5 MHz,
α
]
−
17 (c 1, CHCl3). H-NMR
D
δ
= 7.54 (d, J = 7.6 Hz, 1H), 7.34 (t, J = 7.6 Hz, 1H), 7.01 (t, J = 7.6 Hz, 1H), 6.80
CDCl3):
δ
= 170.9, 156.4, 131.5, 130.9, 123.6 (q, 1JCF = 278.2 Hz), 121.1, 120.8, 111.9, 82.3, 72.7, 55.8 (q,
2JCF = 37.6 Hz), 27.6, 18.2. HRMS (ESI): m/z calculated for C15H19F3N2O3 + H+ [M + H+]: 333.1426.
Found: 333.1425.
tert-Butyl (R)-2-(2-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)propanoate ((R)-54). The similar
treatment of tert-butyl (R)-2-(2-(2,2,2-trifluoro-1-((tosyloxy)imino)ethyl)phenoxy)-propanoate (R)-51 (317 mg,

Molecules 2020, 25, 2790
21 of 25
1
0.65 mmol) as that just described gave (R)-54 (173 mg, 80%). [α]D +17 (c 1, CHCl3). H-NMR (270 MHz,
CDCl3):
δ = 7.54 (d, J = 7.6 Hz, 1H), 7.34 (t, J = 7.6 Hz, 1H), 7.01 (t, J = 7.6 Hz, 1H), 6.80 (d, J = 7.6 Hz,
1H), 4.79 (q, J = 6.8 Hz, 1H), 1.63 (d, J = 6.8 Hz, 3H), 1.36 (s, 9H). 13C-NMR (67.5 MHz, CDCl3): δ = 170.9
,
156.4, 131.5, 130.9, 123.6 (q, 1JCF = 278.8 Hz), 121.1, 120.8, 111.9, 82.3, 72.7, 55.8 (q, 2JCF = 37.4 Hz), 27.6,
18.2. HRMS (ESI): m/z calculated for C15H19F3N2O3 + H+ [M + H+]: 333.1426. Found: 333.1415.
tert-Butyl (S)-2-(4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoate ((S)-55). tert-Butyl
(S)-2-(4-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)propanoate (S)-52 (151 mg, 0.45 mmol) was dissolved
in CH2Cl2 (2 mL). MnO2 (197 mg, 2.27 mmol) was added to the solution, and the reaction mixture
was stirred at room temperature for 2 h, followed by filtration and then concentrated. The residue
was purified by column chromatography (ethyl acetate/n-hexane, 1:9) to give (S)-55 (136 mg, 91%).
1
[
α
]
−
35 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.12 (d, J = 8.6 Hz, 2H), 6.86 (d, J = 8.6 Hz,
D
2H), 4.62 (q, J = 6.8 Hz, 1H), 1.58 (d, J = 6.8 Hz, 3H), 1.43 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
δ = 170.8, 158.8, 128.1, 122.2 (q, 1JCF = 274.9 Hz), 121.6, 115.3, 82.2, 72.9, 28.2 (q, 2JCF = 40.8 Hz), 27.9,
18.3. HRMS (ESI): m/z calculated for C15H17F3N2O3 + H+ [M + H+]: 331.1270. Found: 333.1261. Chiral
HPLC (n-hexane/2-propanol 90:10): tR 15.4 min.
tert-Butyl (R)-2-(4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoate ((R)-55). The similar
treatment of tert-butyl (R)-2-(4-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)-propanoate (R)-52 (201 mg,
1
0.60 mmol) as that just described gave (R)-55 (184 mg, 92%). [
CDCl3):
3H), 1.43 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
α
]
D +35 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 7.12 (d, J = 8.6 Hz, 2H), 6.86 (d, J = 8.6 Hz, 2H), 4.61 (q, J = 6.8 Hz, 1H), 1.58 (d, J = 6.8 Hz,
δ
= 170.8, 158.8, 128.1, 122.2 (q, 1JCF = 274.9 Hz), 121.6,
115.3, 82.2, 72.9, 28.2 (q, 2JCF = 40.8 Hz), 27.9, 18.3. HRMS (ESI): m/z calculated for C15H17F3N2O3 + H+
[M + H+]: 331.1270. Found: 333.1260. Chiral HPLC (n-hexane/2-propanol 90:10): tR 17.1 min.
tert-Butyl (S)-2-(3-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoate ((S)-56). The similar
treatment of tert-butyl (S)-2-(3-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)-propanoate (S)-53 (269 mg,
1
0.81 mmol) as that just described gave (S)-56 (220 mg, 82%). [
CDCl3):
J = 6.8 Hz, 1H), 1.6 (d, J = 6.8 Hz, 3H), 1.4 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
α
]
−
38 (c 1, CHCl3). H-NMR (270 MHz,
D
δ
= 7.3 (t, J = 7.6 Hz, 1H), 6.9 (d, J = 7.6 Hz, 1H), 6.8 (d, J = 7.6 Hz, 1H), 6.7 (s, 1H), 4.6 (q,
= 170.8, 158.0,
130.5, 130.0, 122.1 (q, 1JCF = 274.9 Hz), 119.3, 116.3, 113.2, 82.3, 72.9, 28.3 (q, 2JCF = 40.8 Hz), 27.9, 18.3.
HRMS (ESI): m/z calculated for C15H17F3N2O3 + H+ [M + H+]: 331.1270. Found: 333.1268. Chiral
HPLC (n-hexane/2-propanol 90:10): tR 9.4 min.
δ
tert-Butyl (R)-2-(3-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoate ((R)-56). The similar
treatment of tert-butyl (R)-2-(3-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)-propanoate (R)-53 (347 mg,
1
1.05 mmol) as that just described gave (R)-56 (283 mg, 82%). [
CDCl3):
J = 6.8 Hz, 1H), 1.6 (d, J = 6.8 Hz, 3H), 1.4 (s, 9H). 13C-NMR (67.5 MHz, CDCl3):
α
]
D +38 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 7.3 (t, J = 7.6 Hz, 1H), 6.9 (d, J = 7.6 Hz, 1H), 6.8 (d, J = 7.6 Hz, 1H), 6.7 (s, 1H), 4.6 (q,
= 170.8, 158.0,
130.5, 130.0, 122.1 (q, 1JCF = 274.9 Hz), 119.3, 116.3, 113.2, 82.3, 72.9, 28.3 (q, 2JCF = 40.2 Hz), 27.9, 18.3.
HRMS (ESI): m/z calculated for C15H17F3N2O3 + H+ [M + H+]: 331.1270. Found: 333.1263. Chiral
HPLC (n-hexane/2-propanol 90:10): tR 8.8 min.
δ
tert-Butyl (S)-2-(2-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoate ((S)-57). The similar
treatment of tert-butyl (S)-2-(2-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)-propanoate (S)-54 (105 mg,
1
0.32 mmol) as that just described gave (S)-57 (93.4 mg, 89%). [
α
]
−
10 (c 1, CHCl3). H-NMR (270 MHz,
D
CDCl3):
δ
= 7.37 (d, J = 7.6 Hz, 1H), 7.24 (t, J = 7.6 Hz, 1H), 6.87 (t, J = 7.6 Hz, 1H), 6.66 (d, J = 7.6 Hz,
1H), 4.60 (q, J = 6.8 Hz, 1H), 1.61 (d, J = 6.8 Hz, 3H), 1.30 (s, 9H). 13C-NMR (67.5 MHz, CDCl3): δ = 170.7
,
158.0, 131.7, 131.1, 122.1 (q, 1JCF = 274.9 Hz), 121.3, 117.1, 112.2, 82.1, 73.3, 27.8, 26.4 (q, 2JCF = 43.0 Hz),
18.2. HRMS (ESI): m/z calculated for C15H17F3N2O3 + H+ [M + H+]: 331.1270. Found: 333.1285. Chiral
HPLC (n-hexane/2-propanol 90:10): tR 9.9 min.
tert-Butyl (R)-2-(2-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoate ((R)-57). The similar
treatment of tert-butyl (R)-2-(2-(3-(trifluoromethyl)diaziridin-3-yl)phenoxy)-propanoate (R)-54 (85.8 mg,
1
0.26 mmol) as that just described gave (R)-57 (81.7 mg, 96%). [
CDCl3):
α
]
D +10 (c 1, CHCl3). H-NMR (270 MHz,
δ
= 7.45 (d, J = 7.6 Hz, 1H), 7.33 (t, J = 7.6 Hz, 1H), 6.96 (t, J = 7.6 Hz, 1H), 6.74 (d, J = 7.6 Hz,

Molecules 2020, 25, 2790
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1H), 4.68 (q, J = 6.8 Hz, 1H), 1.69 (d, J = 6.8 Hz, 3H), 1.39 (s, 9H). 13C-NMR (67.5 MHz, CDCl3): δ = 170.7
,
158.0, 131.7, 131.1, 122.1 (q, 1JCF = 274.9 Hz), 121.3, 117.1, 112.2, 82.1, 73.2, 27.8, 26.4 (q, 2JCF = 43.0 Hz),
18.2. HRMS (ESI): m/z calculated for C15H17F3N2O3 + H+ [M + H+]: 331.1270. Found: 333.1276. Chiral
HPLC (n-hexane/2-propanol 90:10): tR 10.3 min.
(S)-2-(4-(3-(Trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoic acid ((S)-58). tert-Butyl (S)-2-(4-(3-
(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoate (S)-55 (165 mg, 0.50 mmol) was dissolved in
CH2Cl2 (1 mL) and then trifluoroacetic acid (2 mL) was added to the solution. After the reaction
mixture was stirred at room temperature for 2 h, the reaction mixture was poured into the cold water
and extracted by CH2Cl2. The organic layer was dried over MgSO4, filtrated and concentrated to
give (S)-58 (135 mg, 98%). [
α
]
−
20 (c 1, CHCl3). 1H-NMR (270 MHz, CDCl3):
δ = 11.33 (s, 1H),
D
7.14 (d, J = 8.6 Hz, 2H), 6.89 (d, J = 8.6 Hz, 2H), 4.79 (q, J = 6.8 Hz, 1H), 1.66 (d, J = 6.8 Hz, 3H).
13C-NMR (67.5 MHz, CDCl3):
δ
= 177.8, 158.2, 128.3, 122.3, 122.2 (q, 1JCF = 274.3 Hz), 115.4, 71.9, 28.1 (q,
2JCF = 40.8 Hz), 18.3. HRMS (ESI): m/z calculated for C11H9F3N2O3 + H+ [M + H+]: 275.0644. Found:
275.0648.
(R)-2-(4-(3-(Trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoic acid ((R)-58).
The similar
treatment of tert-butyl (R)-2-(4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)-propanoate (R)-55 (201 mg,
1
0.61 mmol) as that just described gave (R)-58 (184 mg, 92%). [
α
]
D +20 (c 1, CHCl3). H-NMR (270 MHz,
CDCl3):
δ
= 10.28 (s, 1H), 7.15 (d, J = 8.6 Hz, 2H), 6.89 (d, J = 8.6 Hz, 2H), 4.79 (q, J = 6.8 Hz, 1H), 1.67 (d,
J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3):
δ
= 177.4, 158.2, 128.3, 122.3, 122.2 (q, 1JCF = 274.3 Hz),
115.4, 72.0, 28.1 (q, 2JCF = 40.8 Hz), 18.3. HRMS (ESI): m/z calculated for C11H9F3N2O3 + H+ [M + H+]:
275.0644. Found: 275.0614.
(S)-2-(3-(3-(Trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoic acid ((S)-59).
treatment of tert-butyl (S)-2-(3-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)-propanoate (S)-56 (220 mg,
0.67 mmol) as that just described gave (S)-59 (209 mg, quant). [
13 (c 1, CHCl3). 1H-NMR
(270 MHz, CDCl3): = 11.47 (s, 1H), 7.29 (t, J = 7.8 Hz, 1H), 6.89 (d, J = 7.8 Hz, 1H), 6.79 (d, J = 7.8 Hz,
1H), 6.74 (s, 1H), 4.78 (q, J = 6.8 Hz, 1H), 1.66 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3): δ = 178.0,
The similar
α
]
−
D
δ
1
2
157.5, 130.9, 130.2, 122.0 (q, JCF = 274.7 Hz), 119.8, 115.7, 114.0, 72.1, 28.3 (q, JCF = 39.9 Hz), 18.2.
HRMS (ESI): m/z calculated for C11H9F3N2O3 + H+ [M + H+]: 275.0644. Found: 275.0661.
(R)-2-(3-(3-(Trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoic acid ((R)-59). The similar
treatment of tert-butyl (R)-2-(3-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)-propanoate (R)-56
(283 mg, 0.86 mmol) as that just described gave (R)-59 (208 mg, 89%). [
1H-NMR (270 MHz, CDCl3):
= 11.32 (s, 1H), 7.30 (t, J = 8 Hz, 1H), 6.90 (d, J = 7.8 Hz, 1H),
6.80 (d, J = 7.8 Hz, 1H), 6.74 (s, 1H), 4.78 (q, J = 6.8 Hz, 1H), 1.66 (d, J = 6.8 Hz, 3H). 13C-NMR
α
]
+13 (c 1, CHCl3).
D
δ
(67.5 MHz, CDCl3):
δ
= 177.9, 157.5, 130.9, 130.2, 122.0 (q, 1JCF = 274.5 Hz), 119.8, 115.7, 114.0, 72.1,
28.3 (q, 2JCF = 39.7 Hz), 18.2. HRMS (ESI): m/z calculated for C11H9F3N2O3 + H+ [M + H+]: 275.0644.
Found: 275.0627.
(S)-2-(2-(3-(Trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoic acid ((S)-60). The similar treatment
of tert-butyl (S)-2-(2-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)-propanoate (S)-57 (95.4 mg, 0.29 mmol)
1
as that just described gave (S)-60 (89.0 mg, quant). [
δ
α
]
−
10 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
D
= 7.49 (d, J = 7.6 Hz, 1H), 7.37 (t, J = 7.6 Hz, 1H), 7.02 (t, J = 7.6 Hz, 1H), 6.78 (d, J = 7.6 Hz, 1H),
4.86 (q, J = 6.8 Hz, 1H), 1.78 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3): δ = 177.1, 157.5, 132.0,
131.4 122.0 (q, 1JCF = 275.4 Hz), 122.0, 117.4, 112.4, 72.3, 26.3 (q, 2JCF = 42.5 Hz), 18.2. HRMS (ESI): m/z
calculated for C11H9F3N2O3 + H+ [M + H+]: 275.0644. Found: 275.0663.
(R)-2-(2-(3-(Trifluoromethyl)-3H-diazirin-3-yl)phenoxy)propanoicacid((R)-60). Thesimilartreatment
of tert-butyl (R)-2-(2-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenoxy)-propanoate (R)-57 (166 mg, 0.50 mmol)
1
as that just described gave (R)-60 (151 mg, quant). [
α
]
D
+10 (c 1, CHCl3). H-NMR (270 MHz, CDCl3):
δ
= 7.50 (d, J = 7.6 Hz, 1H), 7.38 (t, J = 7.6 Hz, 1H), 7.03 (t, J = 7.6 Hz, 1H), 6.80 (d, J = 7.6 Hz, 1H),
4.88 (q, J = 6.8 Hz, 1H), 1.77 (d, J = 6.8 Hz, 3H). 13C-NMR (67.5 MHz, CDCl3): δ = 176.6, 157.4, 132.0,
131.3, 122.0, 122.0 (q, 1JCF = 274.9 Hz), 117.3, 112.3, 72.2, 26.3 (q, 2JCF = 42.5 Hz), 18.1. HRMS (ESI): m/z
calculated for C11H9F3N2O3 + H+ [M + H+]: 275.0644. Found: 275.0654.

Molecules 2020, 25, 2790
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4.6. Cell-Based Sweet Taste Assay for Photoreactive Lactisole Derivatives
Construction of cell lines stably expressing the sweet taste receptor. The previously reported
method to construct a cell line stably expressing the human sweet taste receptor [37 38] was also used
in this study. The genes encoding T1R2, T1R3, and G 16gust44 were incorporated into a modified
,
α
version of the pcDNA5/FRT vector (Thermo Fisher Scientific, Waltham, MA, USA.). Following the
Flp-In System protocol (Thermo Fisher Scientific, Waltham, MA, USA.), this construct was transfected
into Flp-In 293 cells.
Measurement of cellular responses. Measurements of cellular responses were performed as
described previously [5,37,38]. At first, all synthesized compounds were prepared in 1 M solution
using dimethyl sulfoxide, and diluted by assay buffer. Cellular responses administrated mixtures
containing both 1 mM aspartame and various concentrations of inhibitors were measured. Flp-In
293 cells stably expressing the sweet taste receptor were seeded in 96-well plates and incubated for an
additional 23 h. The cells were washed with assay buffer and loaded using the FRIPR Calcium 4 Assay
Kit (Molecular Devices, San Jose, CA, USA.). Measurement was performed on FlexStation 3 (Molecular
Devices, San Jose, CA, USA.) after the samples were incubated at 37 ◦C for 1 h. The temperature of the
FlexStation 3 was also maintained at 37 ◦C.
Data analysis. All data were normalized by the cellular response against 1 mM aspartame and
were fitted to Hill’s equation, which was drawn using Clampfit 9.2 (Molecular Devices, Palo Alto, CA,
USA), and IC50 values were calculated from a dose–response curve.
Supplementary Materials: The following are available online, 1H- and 13C- data for synthetic compounds,
Cellular response of each photophore containing lactisole derivatives.
Author Contributions: Conceptualization, T.N., T.M. and M.H.; organic synthesis, A.I., Z.P.T., L.W. and M.H.;
biochemical analysis, T.N., T.M.; data curation, T.N., A.I. and M.H.; writing—original draft preparation, T.N., M.H.
All authors have read and agreed to the published version of the manuscript.
Funding: This research was partially supported by the Ministry of Education, Science, Sports, and Culture
Grant-in-Aid for Scientific Research (C), (17K0194007 M.H.). Part of this work was performed under the
Cooperative Research Program of “Network Joint Research Center for Materials and Devices”. Cross-ministerial
Strategic Innovation Promotion Program (SIP) “Technologies for creating next-generation agriculture, forestry and
fisheries” (T.M.).
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds are available from the authors.
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