Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepidium meyenii): Structural elucidation and concise synthesis of macahydantoin A

Article abstract of DOI:10.1016/j.tetlet.2017.03.038

Macahydantoins A (1) and B (2), two new thiohydantoin derivatives with an unprecedented skeleton, were isolated from maca (Lepidium meyenii). Their structures and absolute configurations were fully established by extensive spectroscopic and computational methods. The totally chemical synthesis of macahydantoin A was achieved via benzylamine and methyl piperidine-3-carboxylate hydrochloride through nucleophilic addition and intramolecular dehydration condensation.

Full text of DOI:10.1016/j.tetlet.2017.03.038

Accepted Manuscript
Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepi-
dium meyenii): structural elucidation and concise synthesis of macahydantoin
A
Mu-Yuan Yu, Xu-Jie Qin, Li-Dong Shao, Xing-Rong Peng, Lei Li, Han Yang,
Ming-Hua Qiu
PII:
S0040-4039(17)30335-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.03.038
TETL 48739
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
9 February 2017
7 March 2017
10 March 2017
Please cite this article as: Yu, M-Y., Qin, X-J., Shao, L-D., Peng, X-R., Li, L., Yang, H., Qiu, M-H., Macahydantoins
A and B, two new thiohydantoin derivatives from Maca (Lepidium meyenii): structural elucidation and concise
synthesis of macahydantoin A, Tetrahedron Letters (2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.03.038
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Graphical Abstract
Macahydantoins A and B, two new
thiohydantoin derivatives from Maca
Leave this area blank for abstract info.
(
Lepidium meyenii): structural elucidation
and concise synthesis of macahydantoin A
Mu-Yuan Yu, Xu-Jie Qin, Li-Dong Shao, Xing-Rong Peng, Lei Li, Han Yang, and Ming-Hua Qiu*

1
Tetrahedron Letters
journal homepage: www.els evier.com
Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepidium
meyenii): structural elucidation and concise synthesis of macahydantoin A
a, b, c, 1
a, c, 1
a, c, 1 a, c
, Xing-Rong Peng , Lei Li
a, b, c
a, c
, Han Yang , and
Mu-Yuan Yu
Ming-Hua Qiu
, Xu-Jie Qin
, Li-Dong Shao
a, c,
∗
a
State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201,
People’s Republic of China
b
University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
c
Yunnan Key Laboratory of Natural Medicinal Chemistry, Kunming 650201, People’s Republic of China
ARTICLE INFO
ABSTRACT
Article history:
Received
Macahydantoins A (1) and B (2), two new thiohydantoin derivatives with an unprecedented
skeleton, were isolated from Maca (Lepidium meyenii). Their structures and absolute
configurations were fully established by extensive spectroscopic and computational methods.
The totally chemical synthesis of macahydantoin A was achieved via benzylamine and methyl
piperidine-3-carboxylate hydrochloride through nucleophilic addition and intramolecular
dehydration condensation.
Received in revised form
Accepted
Available online
Keywords:
Cruciferae
2
017 Elsevier Ltd. All rights reserved.
Lepidium meyenii
Thiohydantoin derivatives
Concise synthesis
Hydantoins are an important class of alkaloids, bearing a
uramido group core fused with a cyclic ring. The structures of
this compound family exhibited diverse bioactivities, such as
antiarrhythmic, antihypertensive, antimycobacterial, anticancer,
1
and antischistosomal effects. Since the first hydantoin was
2
reported in 1861, hydantoins and their derivatives have attracted
great interest from the synthetic and pharmacological
Fig. 1. Chemical structures of 1 and 2.
3
communications. However, hydantoin derivatives have not been
+
ion peak at m/z 261.1058 [M+H] (calcd for C14
H
17ON
2
S,
1
3
obtained from plant species. Maca (Lepidium meyenii), a species
native to Peru region, is usually used as a folk medicine to
enhance sexual behavior, fertility, reduce stress, and menopausal
261.1056) in HRESIMS and C NMR spectrum, implying eight
degrees of unsaturation. With the aid of the HSQC spectrum, the
1
3
C NMR data of 1 showed the signals for one monosubstituted
aromatic ring [δ 137.2 (s, C-2a), 128.4×2 (d, C-4a/6a), 128.0×2
(d, C-3a/7a), and 127.3 (d, C-5a)]. Besides, a carbonyl at δ
171.9 (s, C-3) and a sulfourea carbonyl at δ 192.9 (s, C-1), as
well as five methylenes and one methine were observed in its
4
symptoms. In recent years, maca has been popularly cultivated
C
4
in Lijiang and Dali regions of China for its neuroprotective and
,5
C
6
improve cognitive properties. A phytochemical investigation of
C
1
3
the roots of Lepidium meyenii led to the isolation of two new
thiohydantoin derivatives featuring two parallel nitrogen
heterocyclic six-numbers rings. More importantly, the chemical
synthesis of macahydantoin A was achieved. Herein, we report
the isolation and structural elucidation of macahydantoins A and
B as well as the concise synthesis of macahydantoin A.
C
NMR spectrum. These data accounted for six degrees of
unsaturation, and the remaining two ones indicated the two-
cyclic nature of the molecule. The HMBC correlations of δ
and 5.30 (H -1a) with C-3a, C-7a, C-1, and C-3 verified that the
benzyl unit was connected with N-2. Similarly, HMBC
correlations of δ 4.41 (H-7a) with δ 49.8 (t, C-9) and C-1, of δ
1.99 (H-5b) with C-3, and of δ 3.16 (H-9b) with C-1 and C-3,
H
5.67
2
7
Macahydantoin A (1) was isolated as a light yellow oil. Its
H
C
H
molecular formula was assigned as C14
———
H
16ON
2
S by its molecular
H
∗
Corresponding author at: State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese
Academy of Sciences, Kunming 650201, China
E-mail address: mhchiu@mail.kib.ac.cn (M.-H. Qiu).
These authors contributed equally to this work.
1

2
Tetrahedron Letters
1
0
combined with the substructural fragment of H
1
2
-9–H-4–H
2
-5–
-6 revealed by the H– H COSY spectrum proved the
isothiocyanate with amino acid, and sulfourea with α-
dicarbonyl compound. Considering the presence of a bridged-
1
11
H
2
-6–H
2
construction of two six-numbers rings. Thus, the planar structure
of 1 was established.
ring skeleton, the methods mentioned above could not be adopted
in our synthesis. As shown in Scheme 1, the total synthesis of
macahydantoin A (1) via a facile route was accomplished.
Namely, benzylamine was first treated with carbon disulfide and
sodium hydroxide (NaOH) in dimethylsulfoxide (DMSO) to give
sodium dithiocarbamate; dimethylsulfate was then added and
Unexpectedly, 1 was found to be a racemic mixture through
chiral analysis (Supplementary data, Fig. S23), although its
specific rotation value was +3.2 (c 0.04, MeOH) rather than that
zero. The subsequent chiral HPLC resolution of 1 gave the
anticipated enantiomers (–)-1 and (+)-1, whose ECD curves were
opposite to each other (Fig. 2). Finally, the well matched ECD
curves of (+)-1 and (–)-1 with the calculated ECD curves of 4S-1
and 4R-1 allowed the establishment of the absolute
configurations of 4S for (+)-1 and 4R for (–)-1, respectively.
Therefore, the structure of 1 was determined as shown.
facilely afforded intermidate
3
by using Alagarsamy’s
12
condition. Subsequently, 4 was obtained by refluxing of 3 with
methyl 3-piperidinecarboxylate hydrochloride in ethyl alcohol
(EtOH) in the presence of triethylamine (TEA). Originally, we
tried to acquired the desired skeleton from 4 via the direct
cyclization under the basic condition of n-Butyl lithium, LDA, or
sodium hydroxide aqueous solution. Unfortunately, all these
attempts were all failed. However, the results revealed the fact
that n-Butyl lithium could react with substrate or methyl ester
would be hydrolyzed in aqueous solution of sodium hydroxide.
Consequently, after multiple trials (Supplementary data, Table
S1), an optimal route was established by hydrolyzing 4 to afford
corresponding acid that was further via intermolecular
condensation reaction by using 1-hydroxybenzotriazole (HOBt),
S
N
N
O
1
1
H- H COSY
1
-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and
HMBC
Fig.2. Key 2D NMR correlations and ECD spectra of 1.
dimethylaminopyridine (DMAP) to give macahydantoin A (1)
with a high yield (80%). Finally, macahydantoin A (1) was
obtained by a concise synthesis route with an overall yield of
1
13
3
Table 1. H (600 MHz) and C (150 MHz) NMR data of 1 and 2 in CDCl .
2
3% from benzylamine.
Macahydantoin A (1)
δH (mult., J in Hz)
Macahydantoin B (2)
δH (mult., J in Hz)
No. δC
δC
1
3
4
5
192.9 s
171.9 s
39.6 d 2.82 (1H, br s)
188.1 s
175.6 s
74.8 s
27.8 t
25.6 t
22.0 t
58.3 t
49.9 t
47.9 t
137.2 s
a 2.15 (1H, m)
a 1.98 (1H, m)
b 1.89 (1H, m)
2.13 (2H, m)
b 1.99 (1H, overlapped)
a 1.99 (1H, overlapped)
b 1.63 (1H, m)
6
7
9
1
25.4 t
48.6 t
63.9 t
45.2 t
137.0 s
a 4.41 (1H, dd, 13.5, 3.5)
b 3.49 (1H, m)
a 4.21 (1H, dt, 12.0, 7.4)
b 3.53 (1H, dt, 12.0, 7.4)
a 3.91 (1H, d, 11.6)
b 3.70 (1H, d, 11.6)
a 5.00 (1H, d, 15.0)
b 4.95 (1H, d, 15.0)
a 3.58 (1H, br d, 13.0)
b 3.16 (1H, br d, 13.1)
a 5.67 (1H, d, 14.6)
b 5.30 (1H, d, 14.6)
a
2
3
4
5
6
7
a
a
a
a
a
a
128.0 d 7.22 (1H, m)
128.4 d 7.24 (1H, m)
127.3 d 7.17 (1H, m)
128.4 d 7.24 (1H, m)
128.0 d 7.22 (1H, m)
113.5 d 6.95 (1H, s)
159.6 s
113.4 d 6.79 (1H, dd, 8.3, 1.7)
129.5 d 7.21 (1H, t, 7.9)
120.3 d 7.00 (1H, d, 7.6)
55.2 q 3.77 (3H, s)
Scheme 1. Total synthesis of macahydantoin A (1).
OMe
In addition, the hypothetical biosynthetic pathways of 1 and 2
are illustrated in Scheme 2. Nicotinamide (vitamin B3) could be
recognized as the origin, which condensed with benzoic acid
derivative to give intermediate i. Then i might undergo an achiral
reduction to yield ii which condensed with formaldehyde and
subsequent oxidation may led to iii. This intermediate would be
8
B (2) had the molecular formula of
Macahydantoin
+
13
S by its HRESIMS (m/z 307.1111, [M+H] ) and C
C
15
H
18
O
3
N
2
1
13
NMR data. Comparison of the H and C NMR data of 2 and 1
Table 1) indicated that they were very closely related analogues,
differing in the presence of an additional methoxy group (δ 3.77,
55.2) and an oxyquaternary carbon (δ 74.8). In addition,
HMBC correlations of δ 3.77 with δ 159.6 (s, C-4a) and of δ
.98 (H-5a) and 3.70 (H-9b) with δ 74.8 (s, C-4a) suggested that
(
2
reacted with H S to furnish macahydantoin A (1); otherwise,
H
further oxidation reaction of it may form macahydantoin B (2).
δ
C
C
H
C
H
OH
1
C
R (H or OMe)
O
O
O
O
O
the methoxy group and one hydroxy group were located at C-4a
and C-4, respectively. Further chiral analysis of 2 suggested that
it was also a pair of enatiomer. In the same manner as that of 1, 2
was subsequently separated by a CHIRALPAK ADH column and
the absolute configurations of (+)-2 and (–)-2 (Fig. S1) were
unambiguously established as 4R and 4S by computational
evidence, respectively. Thus, the structure of 2 was elucidated as
shown.
R
R
N
NH2
N
R
N
H
[H]
achiral
HN
N
H
Nicotinamide
i
ii
S
R = H or OMe
N
H
N
N
H
H2S
O
O
O
O
H
R
[
O]
NH HN
1
N
N
S
O
O
MeO
N
iii
ii
Based on the characteristic of chemical skeleton, a three-step
total synthesis route was established after facilitating and
optimizing conditions (Scheme 1). Generally, 2-thiohydantoin
R = H or OMe
R = H or OMe
HO
2
9
Scheme 2. Hypothetical biogenetic pathways of 1 and 2.
derivatives were synthesized by the reactions of rhodanate or

3
Compounds 1 and 2 were tested for their cytotoxicities against
five human cancer cells (HL-60, SMMC-7721, A-549, MCF-7,
(c) Sundaram, G. S. M.; Venkatesh, C.; Ila, H. Synlett. 2006, 2,
51–254.
2. Ware E. Chem Rev. 1950;46:403–470.
(a) Wenzel AG, Jacobsen EN. J. Am. Chem. Soc. 2002;124:
2964–12965;
2
14
and SW480) using the MTT method. Unfortunately, none of
them were active. This also suggested that these minor secondary
metabolites in Maca will not affect its safety as an edible food or
a folk medicine. Moreover, compounds 1 and 2, as well as the
intermidate 4 and its hydrolysis derivative 5 (see Supplementary
data) were evaluated for their antimicrobial activities against
three bacterial strains (S. aureus, E. coli, and P.aeruginosa) and
three fungal strains (A. fumigatus, C. parapsilosis, and C.
3
.
1
(b) Lanman BA, Overman LE, Paulini R, White NS. J Am Chem
Soc. 2007;129:12896–12900;
(
2
c) Spicer JA, Lena G, Lyons DM, et al.
013;56:9542–9555;
d) Wu FR, Jiang H, Zheng BS, et al. J Med Chem. 2015;58:6899–
908.
J Med Chem.
(
6
4. Pino-Figueroa A, Nguyen D, Maher TJ. Ann NY Acad Sci.
2010;1199:77–85.
1
5
albicans). Among them, only 4 showed moderate antibacterial
activity against E. coli with the MIC value of 6.25 µg/mL.
5
.
Rubio J, Dang H, Gong M, Liu X, Chen SL. Food. Chem. Toxicol.
006;6:23–27.
Rubio J, Caidas M, Dávila S, Gasco M, Gonzales GF. BMC
2
In conclusion, macahydantoins A (1) and B (2), two natural
thiohydantoin derivatives with an unprecedant skeleton, were
isolated from Lepidium meyenii. Their structures and absolute
configurations were established using a combination of NMR
spectroscopy and ECD calculations. They were characteristic of a
bridged-ring skeleton linking to a benzyl moiety. To the best of
our knowledge, these compounds were obtained from Cruciferae
family for the first time. Although macamides and macaenes
6
.
Complement Altern Med. 2006;6:23.
2
3
7
.
Macahydantoin A (1): light yellow oil; [α] +3.2 (c 0.03, MeOH);
D
23
23
[
α] D +60.0 (c 0.03, MeOH) for (+)-1; [α] D −54.2 (c 0. 04, MeOH)
for (–)-1; UV (MeOH) λmax (log ε): 264 (3.91), 306 (3.91) nm; IR
KBr) νmax: 3435, 2932, 1660, 1627, 1561, 1532, 1471, 1382, 1242
(
−1
cm ; ECD (MeOH) 255 (∆ε ‒2.1), 271 (∆ε +8.9), 308 (∆ε +1.3)
nm for (+)-1; ECD (MeOH) 225 (∆ε +2.1), 271 (∆ε −8.9), 308 (∆ε
1
13
1
3
−
1.3) nm for (–)-1; H (CDCl
MHz) NMR data, see Table 1; HRESIMS m/z 261.1058 [M+H]
calcd for C14 S, 261.1056).
Macahydantoin B (2): light yellow oil; [α] +2.9 (c 0.08, MeOH);
3
, 600 MHz) and C (CDCl , 150
3
were considered as the characteristic components of maca, our
finding could enrich the diversity of chemical constituents of
maca and even natural resource. Moreover, an efficient total
+
(
H17ON
2
23
8
.
D
synthesis macahydantoins
A (1) was accomplished from
2
3
23
[
α] D (c 0.07, MeOH) +24.2 for (+)-2; [α] D (c 0. 08, MeOH) −23.3
for (–)-2; UV (MeOH) λmax (log ε): 218 (3.48), 245(3.44), 27−13
3.62) nm; IR (KBr) νmax: 3431, 2925, 1747, 1430, 1227 cm ;
commonly available original materials. Although preliminary
cytotoxicity screenings revealed they were inactive, the other
bioactivies of these sulphur-containing alkaloids should further
investigated.
(
ECD (MeOH) 228 (∆ε +6.8), 248 (∆ε −12.7), 274 (∆ε +11.4) nm
for (+)-2; ECD (MeOH) 228 (∆ε −6.8), 248 (∆ε +12.7), 274 (∆ε
1
13
−
11.4) nm for (–)-2; H (CDCl
MHz) NMR data, see Table 1; HRESIMS m/z 307.1127 [M+H]+
calcd for C15 S, 307.1111).
3 3
, 600 MHz) and C (CDCl , 150
Acknowledgements
(
19 3 2
H O N
9
1
.
(a) Marton J, Enisz J, Hosztafi S, Timar T. J Agric Food
Chem.1993;41:148‒152;
(b) Cromwellt, LD, Stark GR. Biochemistry, 1969, 8, 4735-4740.
This research work was financially supported by YiKe R&D
Project (KIB-20140708Q) and Programme of Major New
Productions of Yunnan Province, CHINA (No. 2015BB002). We
are also grateful to Mr. Wang Jin-Song (CEO of Shangri-La Bio-
tech Company) for financial support and the Spectrum Analysis
Centre of Kunming Institute of Botany, Chinese Academy of
Sciences for the measurements of spectroscopic data.
0. Iwata T, Mitoma H, Yamaguchi M. Anal Chim Acta. 2000;416:
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Supplementary Material
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J Nat Prod.
Supplementary data (detailed description of the experimental
procedures, a listing of HRESIMS, 1D and 2D NMR, ECD
spectrum, and chemical synthesis data for compounds 1 and 2)
associated with this article can be found in the online version, at
http://dx.doi.org/10.1016/j.tetlet.
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References
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1
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(a) Marton J, Enisz J, Hosztafi S, Timar T. J Agric Food Chem.
993;41:148–152;
b) Wang CK, Zhao QJ, Vargas M, et al.
016;59:10705–10718;
1
(
J Med Chem.
2

4
Tetrahedron Letters
and B, two novel
Highlights
ꢀ
Macahydantoins
A
thiohydantoin derivatives, were isolated from
Lepidium meyenii.
ꢀ
ꢀ
Stereochemistries were determined by ECD
calculation.
The chemical synthesis of macahydantoin A
was achieved.