Synthesis of N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters

Article abstract of DOI:10.1007/s11164-011-0429-1

Using K₂CO₃ as a base and CH₃CN as solvent, different kinds of N-[5-alkoxy-2(5H)-furanonyl] amino acids were reacted with propargyl bromide via substitution reaction at 40 °C to give 16 N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters with the yields of 44-85% (mostly over 74%). The structures of all newly synthesized compounds were elucidated and confirmed by FTIR, UV, ¹H NMR, C NMR, MS, and elemental analysis. The rapid, efficient, and brief synthesis of the series propargyl esters with multiple bioactive units, will afford not only a basis for the activity test of potential drug molecules, but also an important synthetic strategy for 2(5H)-furanone derivatives with polyfunctional groups. Springer Science+Business Media B.V. 2011.

Full text of DOI:10.1007/s11164-011-0429-1

Res Chem Intermed (2012) 38:925–936
DOI 10.1007/s11164-011-0429-1
Synthesis of N-[5-alkoxy-2(5H)-furanonyl] amino acid
propargyl esters
•
Yue-He Tan Zhao-Yang Wang Ji Qi
•
•
•
Jin-Feng Xiong Mei-Xiang Lv
Received: 15 September 2011 / Accepted: 24 October 2011 / Published online: 16 November 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Using K2CO3 as a base and CH3CN as solvent, different kinds of
N-[5-alkoxy-2(5H)-furanonyl] amino acids were reacted with propargyl bromide via
substitution reaction at 40 °C to give 16 N-[5-alkoxy-2(5H)-furanonyl] amino acid
propargyl esters with the yields of 44–85% (mostly over 74%). The structures of all
1
newly synthesized compounds were elucidated and confirmed by FTIR, UV, H
NMR, 13C NMR, MS, and elemental analysis. The rapid, efficient, and brief syn-
thesis of the series propargyl esters with multiple bioactive units, will afford not
only a basis for the activity test of potential drug molecules, but also an important
synthetic strategy for 2(5H)-furanone derivatives with polyfunctional groups.
Keywords Propargyl ester Á Synthesis Á 2(5H)-Furanone Á Amino acid Á
Substitution reaction Á Polyfunctional groups
Introduction
As an important structural subunit, 2(5H)-furanone is a frequently found in many
natural products. At the same time, many compounds containing 2(5H)-furanone
moiety have been considered as potential insecticides, bactericides, fungicides,
antibiotics, anticancer agents, anti-inflammatories, allergy inhibitors, antisoriasis
agents, and cyclooxygenase inhibitors [1–11].
Electronic supplementary material The online version of this article
(doi:10.1007/s11164-011-0429-1) contains supplementary material, which is
available to authorized users.
Y.-H. Tan Á Z.-Y. Wang (&) Á J. Qi Á J.-F. Xiong Á M.-X. Lv
School of Chemistry and Environment, South China Normal University, Guangzhou 510006,
People’s Republic of China
e-mail: wangwangzhaoyang@tom.com; wangzy@scnu.edu.cn
123

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Y.-H. Tan et al.
It is well known that natural amino acids are important substances for life
activities, and many non-natural amino acids have been used as building blocks
in the fields of organic synthesis, functional material, and medicinal chemistry
[12–16]. Therefore, different amino acids as an effective functional group are often
applied in the design of drug molecules by many researchers [17–22].
At the same time, many compounds containing terminal alkyne structure are not
only important intermediates, especially for the syntheses of different 1,2,3-triazoles
[23–27], but also have different bioactivities [28, 29], and even some propargyl
ester can be used as a herbicide [30]. However, there is no report on the synthesis of
propargyl esters simultaneously containing the structure of 2(5H)-furanone and
amino acid as the bioactive units.
In this article, in order to design and synthesize novel 2(5H)-furanone derivatives
with better biological activity, we tried to combine 2(5H)-furanone, amino acid and
terminal alkyne structure together. Based on our previous studies on the synthesis of
N-[5-alkoxy-2(5H)-furanonyl] amino acids 1a–1p [11, 31], we investigated the
reaction of 1 with propargyl bromide, and synthesized a series of N-[5-alkoxy-
2(5H)-furanonyl] amino acid propargyl esters 2a–2p (Scheme 1).
Results and discussion
Condition optimization for substitution reaction
Usually, amino acid propargyl esters were synthesized via condensation using
N-protected amino acid and propargyl alcohol as materials, and the reported
synthetic methods have many drawbacks, such as higher reaction temperature,
multi-step reaction processes, more expensive reagents, longer reaction times,
especially the tiresome condensing agents for their difficulty in the thorough
separation from the products [32–36].
Br
Br
2
14
11
4
3
15
13
7
H
10
R'
H
6
R'
H
R'
H
O
O
5
O
9
8
COOH
Br
1
COOH
H2N
n
n
COO
Br
Br
n
12
HN
H
HN
H
1
4
1
5
K2CO3, CH3CN
40OC
KOH, EtOH, r.t.
O
1
3
1
O
2
Br
O
R*O
Br
O
R*O
4
3
8
1a~1p
2a~2p
7
6
H
2
9
10
1
1
O
5
O
O
1
a: R*=M*, n=1, R'=H
b: R*=M*, n=1, R'=CH3
c: R*=M*, n=1, R'=CHMe2
i: R*=B*, n=1, R'=H
j
:
R*=B*, n=1, R'=CH3
k
: R*=B*, n=1, R'=CHMe2
R*=
(M*),
(B*)
d
: R*=M*, n=1, R'=CH2CHMe2
: R*=M*, n=1, R'=CH2Ph
l: R*=B*, n=1, R'=CH2CHMe2
m: R*=B*, n=1, R'=CH2Ph
n: R*=B*, n=5, R'=H
e
f: R*=M*, n=5, R'=H
g: R*=M*, n=3, R'=H
o
p
: R*=B*, n=3, R'=H
: R*=B*, n=1, R'=Ph
h
: R*=M*, n=1, R'=Ph
Scheme 1 The synthetic route of the products 2a–2p
123

Synthesis of N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters
927
There are only a few reports on the synthesis of amino acid propargyl esters using
N-protected amino acid and propargyl bromide as materials [37]. Referring to the
reported method [37], we optimized experimental conditions using the substitution
reaction of N-[5-menthyloxy-2(5H)-furanonyl] 6-aminohexanoic acid 1f and
propargyl bromide as an example (Table 1).
Firstly, the dosages of the base K2CO3 were examined (entries 1–3), and the
results indicated that 1.5 equiv. K2CO3 was the most effective. In this case, when
N-[5-menthyloxy-2(5H)-furanonyl] 6-aminohexanoic acid 1f (1 mmol) reacted with
propargyl bromide (2 mmol) in anhydrous DMF at 50 °C for 24 h, the correspond-
ing yield of amino acid ester 2f was 70% (entry 2). Once reducing the base dosage,
the reaction was slightly incomplete.
While excessive base may cause the hydrolysis of propargyl bromide, which
made the yield lowered obviously (entry 3). Even the dosage of the base K2CO3 was
not increased, the addition of water in the solvent also markedly made the yield
lowered (entry 4). This also demonstrated that avoiding the hydrolysis of propargyl
bromide was important. However, different anhydrous solvents could give different
effects.
THF was not a good solvent for the reaction (entry 5). When the reaction was
carried out in DMF or CH3CN, the result was satisfied. Even in CH3CN, the reaction
time could be shortened from 24 to 8 h (entry 7).
The effect of temperature on the reaction was also significant (entries 7–10).
Especially the reaction hardly produced any target product at room temperature
after 8 h (entry 8). While the reactant mixture was heated at 40 °C, the product 2f
was obtained in 74% yield (entry 9), and the results showed that at the higher
temperature, the yield improved no longer (entries 7 and 10).
Thus, when choosing 1.0 equiv. N-[5-menthyloxy-2(5H)-furanonyl] 6-amino-
hexanoic acid 1f and 2.0 equiv. propargyl bromide as the model substrates, the
optimized reaction conditions could be summarized in the following: 40 °C, 8 h 1.5
equiv. K2CO3 as the base, and anhydrous CH3CN as the solvent.
Table 1 Condition optimization for substitution reaction of N-[5-menthyloxy-2(5H)-furanonyl] 6-am-
inohexanoic acid 1f with propargyl bromide
Entry
K2CO3 (equiv.)
Solvent
Temp. (°C)
Time (h)
Yield (%)
1
2
1.0
1.5
2.0
1.5
1.5
1.5
1.5
1.5
1.5
1.5
DMF
50
50
50
50
50
50
50
r.t.
40
60
24
24
24
24
24
24
8
69
DMF
70
3
DMF
60
4
DMF/H2O (2/1)
THF
17
5
30
6
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
73
7
73
8
8
Trace
74
9
8
10
8
73
123

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Y.-H. Tan et al.
Influences of different amino acid material on the yield
Under the optimized conditions, the reactions of a series of N-[2(5H)-furanonyl]
amino acids derived from various natural or unnatural amino acids were examined.
The results showed that whether the main chain of amino acid was long or short, and
whether the side chain of amino acid was alkyl or aryl, the reactions proceeded
smoothly.
In most cases, the yield was higher than (or equal to) 74%. However, the yields of
the compounds 2h and 2p were relatively lower (44–52%). This may be related to
the larger steric hindrance of phenyl in N-[5-alkoxy-2(5H)-furanonyl] (S)-phenyl-
glycine (1h, 1p), which caused the normal reaction slower and made the side-
reaction more obvious.
Structure characterization of the new compounds
In the IR spectra, the N–H groups show stretching absorption in the region of
3240–3387 cm-1, while unsaturated C–H groups of alkynes show stretching
absorption in the region of 3233–3311 cm-1. The weak C:C stretching band of
alkynes occurs in the region of 2127–2133 cm-1 and C–H bending vibration of
alkynes leads to an absorption in the 639–691 cm-1 region.
At the same time, the strong C=O stretching band appears at 1732–1758 cm-1
,
and the C=C stretching band occurs in 1632–1654 cm-1 region. The existence of
C=O and C=C groups was also proved by other test method. In the UV spectra, there
are strong absorption peaks at 267–274 nm region caused by p ? p* transition of
C=C–C=O conjugated system in 2(5H)-furanone ring.
1
In H NMR, there is a triplet at 2.54–2.59 ppm, which is the characteristic peak
of C:CH proton. Furthermore, there is a singlet at 5.71–6.80 ppm from 5-H of
2(5H)-furanone. Combined with other structural characterizations, it could be seen
that the furanone ring was not opened under the above experimental conditions.
Therefore, these characterization not only proved the structure of all newly
synthesized compounds was right as expected, also showed that the concise and
effective synthetic method for propargyl esters simultaneously containing the
structure of 2(5H)-furanone and amino acid as the bioactive units had wide
applicability and strong tolerance for different sensitive groups.
Conclusions
In summary, a series of N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters
have been efficiently synthesized under very mild reaction conditions. The target
compounds possessing multiple bioactive moieties will afford a basis for the activity
test of potential drug molecules. Terminal alkynes are widely used in click reaction
[23–27], Glaser coupling reaction [38–41], Sonogashira reaction [42–45], dimer-
ization [46], even different kinds of addition reactions to C–O and C–N bonds
[47–50]. Thus, the obtained propargyl esters are also important intermediates for
more 2(5H)-furanone derivatives with polyfunctional groups.
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Synthesis of N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters
929
Experimental
General
All the melting points were determined on an X-5 digital melting points apparatus
and were uncorrected. Infrared spectra were recorded on a Bruker Vector 33 FT-IR
instrument by liquid film method in the absorption range of 4000–400 cm-1. 1H and
13C NMR spectra were obtained in CDCl3 on a Varian DRX-400 MHz spectrometer
and tetramethylsilane (TMS) was used as an internal standard. UV absorption peaks
were measured by Shimazu UV-2550 ultraviolet absorption detector with dichlo-
romethane as a solvent. Optical rotations were determined with an Autopol IV
polarimeter in C2H5OH in a 10 cm cell. Elemental analysis was performed on a
Thermo FlashEA TM 112 elemental analyzer. The mass spectra (MS) were recorded
on Thermo LCQ DECA XP MAX mass spectrometer.
All reagents and solvents were commercially available and were used as
received. Using furfural, natural menthol, borneol, and amino acid as starting
materials, the intermediate N-[5-alkoxy-2(5H)-furanonyl] amino acids 1a–1p were
prepared according to the literature [11, 31].
Typical procedure for the synthesis of target compounds 2a–2p
A flame-dried 25-mL round-bottomed flask was charged with 1 mmol N-[5-alkoxy-
2(5H)-furanonyl] amino acid and 1.5 mmol anhydrous potassium carbonate in
CH3CN (5 mL). The resulting suspension was stirred for 30 min under an
atmosphere of nitrogen. Propargyl bromide (80% in toluene, 2 mmol) was added
and the reaction was stirred for 8 h at 40 °C. The resulting mixture was diluted with
water (5 mL), and then extracted with ethyl acetate (10 mL 9 2). The combined
organic layers were dried with magnesium sulfate, and concentrated under vacuum
to give a crude product, which was purified by column chromatography on silica gel
with gradient eluent of mixtures of petroleum ether and ethyl acetate to afford the
sample 2a–2p for analysis.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] glycine propargyl ester (product 2a)
Yellow solid, yield 58%; m.p. 109.8–111.3 °C; [a]2D0 = ?59.54° (c 0.084,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 267 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.77–0.87 (3H, m, CH3-12), 0.86–1.02 (7H, m, CH-13, CH3-14, CH3-15),
1.01–1.23 (2H, m, CH2-9), 1.30–1.48 (2H, m, CH-8, CH-11), 1.58–1.74 (2H, m,
CH2-10), 2.08–2.29 (2H, m, CH2-7), 2.57 (1H, s, CH-21), 3.50–3.65 (1H, m, CH-6),
4.41 (2H, s, CH2-17), 4.83 (2H, s, CH2-19), 5.30 (1H, s, NH-16), 5.76 (1H, s, CH-5);
13C NMR (100 MHz, CDCl3-TMS) d: 15.7, 21.0, 22.1, 22.7, 25.5, 31.5, 33.9, 42.2,
44.5, 48.0, 53.3, 76.0, 76.5, 78.5, 82.2, 98.9, 158.5, 167.7, 168.3; IR (film) m: 3377,
3294, 2955, 2927, 2870, 2131, 1758, 1650, 1330, 1189, 1128, 940, 691, 633;
ESI-MS m/z (%): 428 ([M?H]?, 71.5), 450 ([M?Na]?, 90.3). Anal. Calcd for
C19H26BrNO5: C 53.28, H 6.12, N 3.27; Found: C 53.38, H 6.40, N 3.49.
123

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Y.-H. Tan et al.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] (S)-alanine propargyl ester (product
2b)
Yellow solid, yield 85%, m.p. 106.1–107.4 °C; [a]2D0 = ?151.80° (c 0.057,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 268 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.86 (3H, d, J = 6.8 Hz, CH3-12), 0.88–1.00 (7H, m, CH-13, CH3-14,
CH3-15), 1.01–1.18 (2H, m, CH2-9), 1.33–1.47 (2H, m, CH-8, CH-11), 1.57 (3H, d,
J = 7.2 Hz, CH3-22), 1.63–1.74 (2H, m, CH2-10), 2.08–2.30 (2H, m, CH2-7), 2.57
(1H, s, CH-21), 3.54–3.65 (1H, ddd, J1 = 3.6 Hz, J2 = 4.0 Hz, J3 = 4.0 Hz, CH-
6), 4.80 (2H, d, J = 2.0 Hz, CH2-19), 4.87 (1H, b, NH-16), 5.30–5.41 (1H, m, CH-
17), 5.75 (1H, s, CH-5); 13C NMR (100 MHz, CDCl3-TMS) d: 15.9, 20.5, 20.9,
22.1, 23.0, 26.0, 31.6, 33.9, 42.3, 48.0, 50.7, 53.4, 76.0, 76.5, 82.8, 91.3, 99.2, 156.9,
167.5, 171.3; IR (film) m: 3383, 3289, 2955, 2928, 2871, 2129, 1755, 1652, 1328,
1197, 1134, 960, 674, 633; ESI-MS m/z (%): 442 ([M?H]?, 62.2), 464 ([M?Na]?,
83.0). Anal. Calcd for C20H28BrNO5: C 54.30, H 6.38, N 3.17; Found: C 54.59, H
6.60, N 3.41.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] (S)-valine propargyl ester (product
2c)
Yellow solid, yield 84%, m.p. 76.2–77.8 °C; [a]2D0 = -160.03° (c 0.060,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 269 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.87 (3H, d, J = 6.8 Hz, CH3-12), 0.88–0.98 (7H, m, CH-13, CH3-14,
CH3-15), 0.99–1.28 (8H, m, CH2-9, CH3-23, CH3-24), 1.32–1.49 (2H, m, CH-8,
CH-11), 1.60–1.76 (2H, m, CH2-10), 2.09–2.38 (3H, m, CH2-7, CH-22), 2.56 (1H, s,
CH-21), 3.53–3.64 (1H, ddd, J1 = 3.6 Hz, J2 = 4.0 Hz, J3 = 4.0 Hz, CH-6),
4.60–4.97 (3H, m, NH-16, CH2-19), 5.25 (1H, d, J = 9.2 Hz, CH-17), 5.73 (1H, s,
CH-5); 13C NMR (100 MHz, CDCl3-TMS) d: 15.7, 17.3, 17.9, 20.9, 22.1, 22.8,
25.9, 31.6, 32.4, 33.9, 42.3, 47.9, 53.0, 59.7, 75.9, 76.6, 82.9, 90.6, 99.5, 157.3,
167.6, 170.0; IR (film) m: 3384, 3310, 2957, 2930, 2872, 2129, 1751, 1651, 1329,
1190, 1134, 957, 673, 634; ESI-MS m/z (%): 470 ([M?H]?, 74.1), 492 ([M?Na]?,
80.4). Anal. Calcd for C22H32BrNO5: C 56.17, H 6.86, N 2.98; Found: C 56.40, H
7.05, N 3.16.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] (S)-leucine propargyl ester (product
2d)
Yellow solid, yield 79%, m.p. 124.6–126.0 °C; [a]2D0 = -89.62° (c 0.051,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 267 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.85 (3H, d, J = 7.2 Hz, CH3-12), 0.86–0.97 (7H, m, CH-13, CH3-14,
CH3-15), 0.98–1.29 (8H, m, CH2-9, CH3-24, CH3-25), 1.31–1.49 (2H, m, CH-8,
CH-11), 1.58–1.86 (5H, m, CH2-10, CH2-22, CH-23), 2.06–2.28 (2H, m, CH2-7),
2.55 (1H, t, J = 2.4 Hz, CH-21), 3.53–3.66 (1H, ddd, J1 = 3.2 Hz, J2 = 3.6 Hz,
J3 = 3.6 Hz, CH-6), 4.62–4.93 (3H, m, NH-16, CH2-19), 4.97–5.12 (1H, m, CH-
17), 5.74 (1H, s, CH-5); 13C NMR (100 MHz, CDCl3-TMS) d: 15.9, 20.9, 22.0,
22.1, 22.6, 22.8, 24.7, 25.9, 31.6, 33.9, 42.3, 42.4, 47.9, 53.1, 54.1, 75.9, 76.6, 82.6,
123

Synthesis of N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters
931
91.3, 99.3, 157.5, 167.5, 171.2; IR (film) m: 3311, 2957, 2929, 2871, 2129, 1754,
1651, 1331, 1185, 1130, 962, 671, 508; ESI-MS m/z (%): 484 ([M?H]?, 89.3), 506
([M?Na]?, 90.2). Anal. Calcd for C23H34BrNO5: C 57.03, H 7.07, N 2.89; Found:
C 57.30, H 7.36, N 3.15.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] (S)-phenylalanine propargyl ester
(product 2e)
Yellow solid, yield 83%, m.p. 99.8–101.5 °C; [a]2D0 = ?75.04° (c 0.061,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 269 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.74 (3H, d, J = 4.0 Hz, CH3-12), 0.78–0.94 (7H, m, CH-13, CH3-14,
CH3-15), 0.95–1.19 (2H, m, CH2-9), 1.26–1.44 (2H, m, CH-8, CH-11), 1.56–1.71
(2H, m, CH2-10), 1.86–2.23 (2H, m, CH2-7), 2.58 (1H, s, CH-21), 3.03–3.31 (2H,
m, CH2-22), 3.37–3.49 (1H, m, CH-6), 4.79 (2H, s, CH2-19), 4.87–5.46 (3H, m, CH-
5, NH-16, CH-17), 7.00–7.20 (2H, m, Ar–H-24, 28), 7.21–7.44 (3H, m, Ar–H-25,
26, 27); 13C NMR (100 MHz, CDCl3-TMS) d: 15.5, 21.1, 22.1, 22.6, 25.5, 31.6,
33.9, 40.1, 42.3, 47.9, 53.3, 56.1, 76.2, 76.4, 83.0, 99.3, 105.0, 127.8, 128.9, 129.6,
134.1, 157.0, 167.4, 169.6; IR (film) m: 3386, 3294, 3062, 3024, 2955, 2925, 2876,
2127, 1758, 1654, 1524, 1454, 1327, 1182, 1116, 955, 744, 702, 683; ESI-MS
m/z (%): 518 ([M?H]?, 61.6), 540 ([M?Na]?, 100.0). Anal. Calcd for C26H32
BrNO5: C 60.23, H 6.22, N 2.70; Found: C 59.96, H 6.44, N 2.99.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] 6-aminohexanoic acid propargyl
ester (product 2f)
Yellow solid, yield 74%, m.p. 122.5–124.0 °C; [a]2D0 = ?141.20° (c 0.114,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 273 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.81 (3H, d, J = 6.8 Hz, CH3-12), 0.84–0.98 (7H, m, CH-13, CH3-14,
CH3-15), 0.99–1.19 (2H, m, CH2-9), 1.30–1.48 (4H, m, CH-8, CH-11, CH2-19),
1.60–1.78 (6H, m, CH2-10, CH2-18, CH2-20), 2.09–2.29 (2H, m, CH2-7), 2.40 (2H,
t, J = 7.2 Hz, CH2-21), 2.50 (1H, s, CH-25), 3.40–3.53 (2H, m, CH2-17), 3.54–3.63
(1H, ddd, J1 = 3.6 Hz, J2 = 3.6 Hz, J3 = 4.0 Hz, CH-6), 4.69 (2H, d, J = 2.0 Hz,
CH2-23), 4.84–4.99 (1H, m, NH-16), 5.75 (1H, s, CH-5); 13C NMR (100 MHz,
CDCl3-TMS) d: 15.9, 21.1, 22.1, 22.8, 24.2, 25.5, 25.8, 30.3, 31.6, 33.6, 33.9, 42.4,
43.6, 48.1, 51.9, 74.9, 77.6, 81.8, 89.4, 98.5, 159.3, 167.8, 172.5; IR (film) m: 3241,
2952, 2917, 2868, 2131, 1733, 1649, 1315, 1154, 1124, 937, 675, 630; ESI-MS
m/z (%): 484 ([M?H]?, 31.0), 506 ([M?Na]?, 100.0). Anal. Calcd for C23H34
BrNO5: C 57.03, H 7.07, N 2.89; Found: C 56.91, H 7.30, N 3.00.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] 4-aminobutyric acid propargyl ester
(product 2g)
Yellowish solid, yield 69%, m.p. 92.9–94.5 °C; [a]2D0 = ?68.21° (c 0.029,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 274 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.81 (3H, d, J = 6.8 Hz, CH3-12), 0.83–0.99 (7H, m, CH-13, CH3-14,
CH3-15), 1.00–1.20 (2H, m, CH2-9), 1.29–1.46 (2H, m, CH-8, CH-11), 1.59–1.75
123

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Y.-H. Tan et al.
(2H, m, CH2-10), 1.92–2.07 (2H, m, CH2-18), 2.09–2.30 (2H, m, CH2-7), 2.32–2.64
(3H, m, CH2-19, CH-23), 3.45–3.73 (3H, m, CH-6, CH2-17), 4.71 (2H, d,
J = 2.0 Hz, CH2-21), 5.14–5.29 (1H, m, NH-16), 5.77 (1H, s, CH-5); 13C NMR
(100 MHz, CDCl3-TMS) d: 15.8, 21.1, 22.1, 22.8, 25.3, 25.5, 30.8, 31.6, 33.9, 42.4,
43.1, 48.1, 52.2, 75.2, 77.3, 81.8, 88.1, 98.5, 159.4, 167.9, 172.2; IR (film) m: 3277,
3233, 2953, 2926, 2869, 2129, 1733, 1647, 1316, 1162, 1125, 955, 686, 639;
ESI-MS m/z (%): 456 ([M?H]?, 74.0), 478 ([M?Na]?, 75.6). Anal. Calcd for
C21H30BrNO5: C 55.27, H 6.63, N 3.07; Found: C 55.33, H 6.50, N 3.12.
N-[3-Bromo-5-(S)-menthoxy-2(5H)-furanonyl] (S)-phenylglycine propargyl ester
(product 2h)
Yellow liquid, yield 52%; [a]D20 = 111.5° (c 0.026, CH3CH2OH); UV–Vis (CH2Cl2)
1
k
max: 270 nm; H NMR (400 MHz, CDCl3-TMS) d: 0.83–0.88 (3H, m, CH3-12),
0.89–1.01 (7H, m, CH-13, CH3-14, CH3-15), 1.03–1.18 (2H, m, CH2-9), 1.35–1.47
(2H, m, CH-8, CH-11), 1.62–1.74 (2H, m, CH2-10), 2.12–2.31 (2H, m, CH2-7),
2.45–2.58 (1H, m, CH-21), 3.51–3.68 (1H, m, CH-6), 4.62–4.88 (2H, m, CH2-19),
5.58–5.92 (3H, m, CH-5, NH-16, CH-17), 7.30–7.40 (2H, m, Ar–H-23, 27),
7.39–7.51 (3H, m, Ar–H-24, 25, 26); 13C NMR (100 MHz, CDCl3-TMS) d: 15.9,
21.0, 22.1, 22.8, 25.8, 31.6, 33.9, 42.1, 48.0, 53.8, 58.5, 72.8, 76.1, 76.2, 83.1, 100.7,
126.9, 129.3, 129.4, 135.4, 155.1, 167.5, 169.4; IR (film) m: 3373, 3290, 3069, 2955,
2929, 2867, 2129, 1754, 1654, 1514, 1455, 1318, 1167, 1123, 960, 746, 696, 517;
ESI-MS m/z (%): 504 ([M?H]?, 56.0), 526 ([M?Na]?, 95.6). Anal. Calcd for
C25H30BrNO5: C 59.53, H 5.99, N 2.78; Found: C 59.46, H 6.05, N 2.71.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] glycine propargyl ester (product 2i)
Yellow solid, yield 63%, m.p. 152.0–152.5 °C; [a]2D0 = ?101.25° (c 0.053,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 268 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.86 (6H, s, CH3-14, CH3-15), 0.91 (3H, s, CH3-12), 1.18–1.36 (4H, m,
CH2-8, CH2-9), 1.65–1.75 (2H, m, CH2-11), 2.22–2.32 (1H, m, CH-10), 2.56 (1H, t,
J = 2.4 Hz, CH-21), 3.94–4.03 (1H, m, CH-6), 4.36 (2H, s, CH2-17), 4.82 (2H, t,
J = 2.0 Hz, CH2-19), 5.39–5.48 (1H, m, NH-16), 5.76 (1H, s, CH-5); 13C NMR
(100 MHz, CDCl3-TMS) d: 13.9, 18.8, 19.6, 26.5, 27.9, 37.0, 44.6, 44.8, 47.6, 49.4,
53.2, 76.0, 76.6, 77.4, 87.8, 99.4, 158.9, 167.6, 168.5; IR (film) m: 3365, 3294, 2953,
2878, 2133, 1758, 1649, 1322, 1185, 1132, 943, 682, 628; ESI-MS m/z (%): 426
([M?H]?, 32.5), 448 ([M?Na]?, 100.0). Anal. Calcd for C19H24BrNO5: C 53.53, H
5.67, N 3.29; Found: C 53.36, H 5.71, N 3.50.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] (S)-alanine propargyl ester
(product 2j)
Yellow solid, yield 74%, m.p. 120.9–122.3 °C; [a]2D0 = 54.50° (c 0.059,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 267 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.86 (6H, s, CH3-14, CH3-15), 0.92 (3H, s, CH3-12), 1.21–1.32 (4H, m,
CH2-8, CH2-9), 1.58 (3H, d, J = 7.2 Hz, CH3-22), 1.63–1.76 (2H, m, CH2-11),
123

Synthesis of N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters
933
2.20–2.31 (1H, m, CH-10), 2.56 (1H, t, J = 2.4 Hz, CH-21), 3.98 (1H, d,
J = 8.8 Hz, CH-6), 4.69–4.88 (3H, m, NH-16, CH2-19), 5.39–5.51 (1H, m, CH-17),
5.76 (1H, s, CH-5); 13C NMR (100 MHz, CDCl3-TMS) d: 13.9, 18.8, 19.6, 20.1,
26.5, 27.9, 37.1, 44.8, 47.6, 49.4, 51.1, 53.3, 68.8, 76.0, 76.5, 87.7, 99.3, 157.5,
167.3, 171.3; IR (film) m: 3289, 2954, 2878, 2131, 1755, 1652, 1330, 1197, 1137,
958, 687, 642; ESI-MS m/z (%): 440 ([M?H]?, 74.8), 462 ([M?Na]?, 65.0). Anal.
Calcd for C20H26BrNO5: C 54.55, H 5.95, N 3.18; Found: C 54.76, H 5.80, N 3.01.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] (S)-valine propargyl ester
(product 2k)
Yellow solid, yield 74%, m.p. 118.9–120.4 °C; [a]2D0 = -151.2° (c 0.095,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 268 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.87 (6H, s, CH3-14, CH3-15), 0.94 (3H, s, CH3-12), 1.03 (6H, d,
J = 6.8 Hz, CH3-23, CH3-24), 1.21–1.32 (4H, m, CH2-8, CH2-9), 1.63–1.76 (2H,
m, CH2-11), 1.77–1.89 (1H, m, CH-22), 2.20–2.34 (1H, m, CH-10), 2.55 (1H, s,
CH-21), 3.99 (1H, d, J = 9.6 Hz, CH-6), 4.65–4.92 (3H, m, NH-16, CH2-19), 5.30
(1H, d, J = 10.0 Hz, CH-17), 5.72 (1H, s, CH-5); 13C NMR (100 MHz, CDCl3-
TMS) d: 13.9, 17.4, 18.2, 18.8, 19.6, 26.5, 27.9, 32.3, 37.0, 44.8, 47.5, 49.4, 52.9,
60.3, 68.8, 75.9, 76.6, 88.0, 99.5, 157.9, 167.2, 170.0; IR (film) m: 3388, 3298, 2957,
2878, 2129, 1753, 1654, 1332, 1191, 1135, 957, 675, 581; ESI-MS m/z (%): 468
([M?H]?, 75.7), 490 ([M?Na]?, 82.6). Anal. Calcd for C22H30BrNO5: C 56.41, H
6.46, N 2.99; Found: C 56.20, H 6.61, N 3.28.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] (S)-leucine propargyl ester
(product 2l)
Yellow liquid, yield 82%; [a]2D0 = -102.3° (c 0.059, CH3CH2OH); UV–Vis
(CH2Cl2) kmax: 269 nm; 1H NMR (400 MHz, CDCl3-TMS) d: 0.86 (6H, s, CH3-14,
CH3-15), 0.92 (3H, s, CH3-12), 0.94–1.08 (6H, m, CH3-24, CH3-25), 1.12–1.37 (4H,
m, CH2-8, CH2-9), 1.64–1.81 (5H, m, CH2-11, CH2-22, CH-23), 2.21–2.33 (1H, m,
CH-10), 2.55 (1H, t, J = 2.4 Hz, CH-21), 3.98 (1H, d, J = 8.4 Hz, CH-6),
4.60–4.91 (3H, m, NH-16, CH2-19), 5.14–5.28 (1H, m, CH-17), 5.72 (1H, s, CH-5);
13C NMR (100 MHz, CDCl3-TMS) d: 13.9, 18.8, 19.6, 21.9, 22.8, 24.7, 26.4, 27.9,
37.1, 42.4, 44.8, 47.6, 49.4, 53.1, 54.4, 75.9, 76.6, 77.3, 88.1, 99.4, 158.0, 167.2,
171.2; IR (film), m: 3293, 2956, 2877, 2133, 1754, 1648, 1334, 1146, 958, 676, 580;
ESI-Ms, m/z (%): 482 ([M?H]?, 60.4), 504 ([M?Na]?, 82.1). Anal. Calcd for
C23H32BrNO5: C 57.26, H 6.69, N 2.90; Found: C 57.49, H 6.91, N 3.04.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] (S)-phenylalanine propargyl ester
(product 2m)
Yellow liquid, yield 80%; [a]D20 = 83.78° (c 0.025, CH3CH2OH); UV–Vis (CH2Cl2)
1
k
CH3-14, CH3-15), 1.17–1.29 (4H, m, CH2-8, CH2-9), 1.61–1.74 (2H, m, CH2-11),
max: 271 nm; H NMR (400 MHz, CDCl3-TMS) d: 0.77–0.94 (9H, m, CH3-12,
2.11–2.26 (1H, m, CH-10), 2.58 (1H, t, J = 2.4 Hz, CH-21), 3.06–3.35 (2H, m,
123

934
Y.-H. Tan et al.
CH2-22), 3.73–3.88 (1H, m, CH-6), 4.74–4.87 (2H, m, CH2-19), 4.88–5.54 (3H, m,
CH-5, NH-16, CH-17), 7.09–7.23 (2H, m, Ar–H-24, 28), 7.26–7.45 (3H, m, Ar–H-
25, 26, 27); 13C NMR (100 MHz, CDCl3-TMS) d: 14.1, 18.7, 19.6, 26.5, 27.9, 36.9,
40.0, 44.8, 47.6, 49.4, 53.4, 56.8, 72.8, 76.1, 76.4, 88.2, 99.4, 127.9, 129.0, 129.5,
134.5, 157.2, 167.2, 169.7; IR (film) m: 3372, 3294, 3064, 3029, 2953, 2881, 2130,
1755, 1651, 1523, 1497, 1455, 1336, 1176, 1131, 958, 745, 703, 640, 502; ESI-MS
m/z (%): 516 ([M?H]?, 68.1), 538 ([M?Na]?, 75.1). Anal. Calcd for
C26H30BrNO5: C 60.47, H 5.86, N 2.71; Found: C 60.35, H 5.71, N 2.90.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] 6-aminohexanoic acid propargyl
ester (product 2n)
Yellow solid, yield 81%, m.p. 93.1–94.5 °C; [a]2D0 = 15.27° (c 0.055, CH3CH2OH);
UV–Vis (CH2Cl2) kmax: 273 nm; 1H NMR (400 MHz, CDCl3-TMS) d: 0.86 (6H, s,
CH3-14, CH3-15), 0.90 (3H, s, CH3-12), 1.18–1.36 (4H, m, CH2-8, CH2-9),
1.38–1.48 (2H, m, CH2-19), 1.60–1.77 (6H, m, CH2-11, CH2-18, CH2-20),
2.21–2.32 (1H, m, CH-10), 2.40 (2H, t, J = 7.2 Hz, CH2-21), 2.50 (1H, t,
J = 2.4 Hz, CH-25), 3.38–3.58 (2H, m, CH2-17), 3.99 (1H, d, J = 9.2 Hz, CH-6),
4.69 (2H, d, J = 2.4 Hz, CH2-23), 5.11 (1H, s, NH-16), 5.75 (1H, s, CH-5); 13C
NMR (100 MHz, CDCl3-TMS) d: 14.0, 18.8, 19.6, 24.2, 25.8, 26.6, 28.0, 30.3, 33.6,
37.1, 43.9, 44.8, 47.6, 49.4, 51.9, 67.5, 74.9, 77.6, 87.5, 99.1, 160.0, 167.6, 172.5; IR
(film) m: 3298, 2951, 2878, 2132, 1747, 1644, 1321, 1151, 1133, 954, 679, 639;
ESI-MS m/z (%): 482 ([M?H]?, 49.2), 504 ([M?Na]?, 84.1). Anal. Calcd for
C23H32BrNO5: C 57.26, H 6.69, N 2.90; Found: C 56.97, H 6.76, N 3.00.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] 4-aminobutyric acid propargyl ester
(product 2o)
Yellow solid, yield 76%, m.p. 140.9–142.1 °C; [a]2D0 = 160.25° (c 0.059,
CH3CH2OH); UV–Vis (CH2Cl2) kmax: 272 nm; 1H NMR (400 MHz, CDCl3-
TMS) d: 0.86 (3H, s, CH3-14), 0.87 (3H, s, CH3-15), 0.90 (3H, s, CH3-12),
1.16–1.35 (4H, m, CH2-8, CH2-9), 1.63–1.76 (2H, m, CH2-11), 1.95–2.07 (2H, m,
CH2-18), 2.20–2.31 (1H, m, CH-10), 2.43–2.59 (3H, m, CH2-19, CH-23), 3.46–3.62
(2H, m, CH-17), 3.99 (1H, d, J = 8.8 Hz, CH-6), 4.71 (2H, d, J = 2.4 Hz, CH2-21),
5.31 (1H, s, NH-16), 5.75 (1H, s, CH-5); 13C NMR (100 MHz, CDCl3-TMS) d:
14.0, 18.8, 19.6, 25.3, 26.6, 28.0, 30.9, 37.0, 43.3, 44.8, 47.6, 49.4, 52.3, 67.9, 75.2,
77.3, 87.6, 99.2, 159.5, 167.7, 172.2; IR (film) m: 3254, 2957, 2876, 2130, 1734,
1633, 1321, 1163, 1131, 953, 635, 604; ESI-MS m/z (%): 454 ([M?H]?, 87.0), 476
([M?Na]?, 100.0). Anal. Calcd for C21H28BrNO5: C 55.51, H 6.21, N 3.08; Found:
C 55.80, H 6.42, N 3.30.
N-[3-Bromo-5-(S)-bornyloxy-2(5H)-furanonyl] (S)-phenylglycine propargyl ester
(product 2p)
Yellow liquid, yield 44%; [a]D20 = 157.6° (c 0.039, CH3CH2OH); UV–Vis (CH2Cl2)
1
k
max: 268 nm; H NMR (400 MHz, CDCl3-TMS) d: 0.82–1.02 (9H, m, CH3-12,
123

Synthesis of N-[5-alkoxy-2(5H)-furanonyl] amino acid propargyl esters
935
CH3-14, CH3-15), 1.20–1.38 (4H, m, CH2-8, CH2-9), 1.61–1.80 (2H, m, CH2-11),
2.12–2.30 (1H, m, CH-10), 2.43–2.57 (1H, m, CH-21), 3.70–4.02 (1H, m, CH-6),
4.62–4.87 (2H, m, CH2-19), 5.29–5.71 (1H, m, NH-16), 5.73–6.09 (1H, m, CH-17),
6.80 (1H, s, CH-5), 7.32–7.53 (5H, m, Ar–H); 13C NMR (100 MHz, CDCl3-TMS)
d: 14.1, 18.8, 19.6, 26.7, 28.0, 36.9, 44.8, 47.6, 49.5, 54.7, 58.5, 72.8, 76.2, 76.3,
88.1, 101.1, 126.6, 129.0, 129.3, 136.4, 155.4, 169.4, 170.4; IR (film) m: 3360, 3295,
3070, 3035, 2953, 2877, 2130, 1758, 1653, 1516, 1453, 1333, 1183, 1132, 962, 745,
696, 659, 559; ESI-MS m/z (%): 502 ([M?H]?, 22.5), 540 ([M?K]?, 74.3). Anal.
Calcd for C25H28BrNO5: C 59.77, H 5.62, N 2.79; Found: C 59.80, H 5.57, N 2.82.
Acknowledgments We are grateful to the National Natural Science Foundation of China (No.
20772035) and the Natural Science Foundation of Guangdong Province (No. 5300082) for financial
support.
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