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Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepidium meyenii): Structural elucidation and concise synthesis of macahydantoin A
Accepted Manuscript Macahydantoins A and B, two new thiohydantoin derivatives from Maca (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, Ming-Hua Qiu PII: DOI: Reference:
S0040-4039(17)30335-0 http://dx.doi.org/10.1016/j.tetlet.2017.03.038 TETL 48739
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
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Graphical Abstract
Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepidium meyenii): structural elucidation and concise synthesis of macahydantoin A
Leave this area blank for abstract info.
Mu-Yuan Yu, Xu-Jie Qin, Li-Dong Shao, Xing-Rong Peng, Lei Li, Han Yang, and Ming-Hua Qiu*
1
Tetrahedron Letters j o ur n al h om e p a g e : w w w . e l s e v i er . c o m
Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepidium meyenii): structural elucidation and concise synthesis of macahydantoin A Mu-Yuan Yu a, b, c, 1, Xu-Jie Qin a, c, 1, Li-Dong Shao a, c, 1, Xing-Rong Peng a, c, Lei Li a, b, c, Han Yang a, c, and Ming-Hua Qiu 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
A R T IC LE IN F O
A B S TR A C T
Art icle history: Received Received in revised form Accepted Available online
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.
Keywords: Cruciferae 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, and antischistosomal effects.1 Since the first hydantoin was reported in 1861,2 hydantoins and their derivatives have attracted great interest from the synthetic and pharmacological communications.3 However, hydantoin derivatives have not been 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 symptoms.4 In recent years, maca has been popularly cultivated in Lijiang and Dali regions of China for its neuroprotective4,5 and improve cognitive properties.6 A phytochemical investigation of 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. Macahydantoin A (1)7 was isolated as a light yellow oil. Its molecular formula was assigned as C14H16ON2S by its molecular
———
2017 Elsevier Ltd. All rights reserved.
Fig. 1. Chemical structures of 1 and 2.
ion peak at m/z 261.1058 [M+H]+ (calcd for C14H17ON2S, 261.1056) in HRESIMS and 13C NMR spectrum, implying eight degrees of unsaturation. With the aid of the HSQC spectrum, the 13 C NMR data of 1 showed the signals for one monosubstituted aromatic ring [δC 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 δC 171.9 (s, C-3) and a sulfourea carbonyl at δC 192.9 (s, C-1), as well as five methylenes and one methine were observed in its 13C NMR spectrum. These data accounted for six degrees of unsaturation, and the remaining two ones indicated the twocyclic nature of the molecule. The HMBC correlations of δH 5.67 and 5.30 (H2-1a) with C-3a, C-7a, C-1, and C-3 verified that the benzyl unit was connected with N-2. Similarly, HMBC correlations of δH 4.41 (H-7a) with δC 49.8 (t, C-9) and C-1, of δH 1.99 (H-5b) with C-3, and of δH 3.16 (H-9b) with C-1 and C-3,
∗ 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: [email protected] (M.-H. Qiu). 1 These authors contributed equally to this work.
2
Tetrahedron Letters
combined with the substructural fragment of H2-9–H-4–H2-5– H2-6–H2-6 revealed by the 1H–1H COSY spectrum proved the construction of two six-numbers rings. Thus, the planar structure of 1 was established. 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.
S N
N
O 1
H-1H COSY HMBC
Fig.2. Key 2D NMR correlations and ECD spectra of 1. Table 1. 1H (600 MHz) and 13C (150 MHz) NMR data of 1 and 2 in CDCl3. No. 1 3 4 5 6 7 9 1a 2a 3a 4a 5a 6a 7a OMe
Macahydantoin A (1) δC δH (mult., J in Hz) 192.9 s 171.9 s 39.6 d 2.82 (1H, br s) 25.6 t a 2.15 (1H, m) b 1.99 (1H, overlapped) 22.0 t a 1.99 (1H, overlapped) b 1.63 (1H, m) 58.3 t a 4.41 (1H, dd, 13.5, 3.5) b 3.49 (1H, m) 49.9 t a 3.58 (1H, br d, 13.0) b 3.16 (1H, br d, 13.1) 47.9 t a 5.67 (1H, d, 14.6) b 5.30 (1H, d, 14.6) 137.2 s 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)
isothiocyanate10 with amino acid, and sulfourea with αdicarbonyl compound. 11 Considering the presence of a bridgedring 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 facilely afforded intermidate 3 by using Alagarsamy’s condition. 12 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), 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and 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 23% from benzylamine.
Macahydantoin B (2) δC δH (mult., J in Hz) 188.1 s 175.6 s 74.8 s 27.8 t a 1.98 (1H, m) b 1.89 (1H, m) 25.4 t 2.13 (2H, m) 48.6 t 63.9 t 45.2 t 137.0 s 113.5 d 159.6 s 113.4 d 129.5 d 120.3 d 55.2 q
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) 6.95 (1H, s) 6.79 (1H, dd, 8.3, 1.7) 7.21 (1H, t, 7.9) 7.00 (1H, d, 7.6) 3.77 (3H, s)
Macahydantoin B (2)8 had the molecular formula of C15H18O3 N2S by its HRESIMS (m/z 307.1111, [M+H]+) and 13C NMR data. Comparison of the 1H and 13C 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 (δH 3.77, δC 55.2) and an oxyquaternary carbon (δC 74.8). In addition, HMBC correlations of δH 3.77 with δC 159.6 (s, C-4a) and of δH 1.98 (H-5a) and 3.70 (H-9b) with δC 74.8 (s, C-4a) suggested that 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. 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 derivatives were synthesized by the reactions of rhodanate9 or
Scheme 1. Total synthesis of macahydantoin A (1).
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 reacted with H2S to furnish macahydantoin A (1); otherwise, further oxidation reaction of it may form macahydantoin B (2). OH
N
R (H or OMe)
O
O
NH2
N
S N
N
N O HO 2
O R [H]
HN
achiral
H2S -H O 2 R
H 1 S
MeO
O N H
i R = H or OMe
Nicotinamide
O
O
N
-H 2O [O ]
N
R
N H ii H
O N
O iii R = H or OMe
[O]
R
O
H
NH HN O ii R = H or OMe
Scheme 2. Hypothetical biogenetic pathways of 1 and 2.
3 Compounds 1 and 2 were tested for their cytotoxicities against five human cancer cells (HL-60, SMMC-7721, A-549, MCF-7, and SW480) using the MTT method.14 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. albicans).15 Among them, only 4 showed moderate antibacterial activity against E. coli with the MIC value of 6.25 µg/mL. 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 were considered as the characteristic components of maca,13 our finding could enrich the diversity of chemical constituents of maca and even natural resource. Moreover, an efficient total synthesis macahydantoins A (1) was accomplished from commonly available original materials. Although preliminary cytotoxicity screenings revealed they were inactive, the other bioactivies of these sulphur-containing alkaloids should further investigated.
7.
(c) Sundaram, G. S. M.; Venkatesh, C.; Ila, H. Synlett. 2006, 2, 251–254. Ware E. Chem Rev. 1950;46:403–470. (a) Wenzel AG, Jacobsen EN. J. Am. Chem. Soc. 2002;124: 12964–12965; (b) Lanman BA, Overman LE, Paulini R, White NS. J Am Chem Soc. 2007;129:12896–12900; (c) Spicer JA, Lena G, Lyons DM, et al. J Med Chem. 2013;56:9542–9555; (d) Wu FR, Jiang H, Zheng BS, et al. J Med Chem. 2015;58:6899– 6908. Pino-Figueroa A, Nguyen D, Maher TJ. Ann NY Acad Sci. 2010;1199:77–85. Rubio J, Dang H, Gong M, Liu X, Chen SL. Food. Chem. Toxicol. 2006;6:23–27. Rubio J, Caidas M, Dávila S, Gasco M, Gonzales GF. BMC Complement Altern Med. 2006;6:23. 23 Macahydantoin A (1): light yellow oil; [α] D +3.2 (c 0.03, MeOH);
8.
[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 cm−1 ; 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 −1.3) nm for (–)-1; 1 H (CDCl3 , 600 MHz) and 13C (CDCl 3, 150 MHz) NMR data, see Table 1; HRESIMS m/z 261.1058 [M+H]+ (calcd for C14 H17 ON2S, 261.1056). 23 Macahydantoin B (2): light yellow oil; [α] D +2.9 (c 0.08, MeOH);
2. 3.
4. 5. 6.
Acknowledgements 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 Biotech Company) for financial support and the Spectrum Analysis Centre of Kunming Institute of Botany, Chinese Academy of Sciences for the measurements of spectroscopic data.
9.
10. 11. 12. 13.
Supplementary Material 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.
14. 15.
23
23
23
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), 273 (3.62) nm; IR (KBr) νmax: 3431, 2925, 1747, 1430, 1227 cm−1; 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 −11.4) nm for (–)-2; 1H (CDCl 3, 600 MHz) and 13C (CDCl 3, 150 MHz) NMR data, see Table 1; HRESIMS m/z 307.1127 [M+H]+ (calcd for C15 H19 O3 N2 S, 307.1111). (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. Iwata T, Mitoma H, Yamaguchi M. Anal Chim Acta. 2000;416: 69‒75. Tompkins JE. J Med Chem. 1986;29:855–859. Alagarsamy V, Solomon VR, Murugan, M. Bioorg Med Chem. 2007;15:4009‒4015. (a) Zhao JP, Muhammad I, Dunbar DC, Mustafa J, Khah IA. J Agric Food Chem. 2005;53:690‒693; (b) Chain, F E, Grau A, Martins J C, Catalan CAN. Phytochemistry Lett. 2014;8:145‒148; (c) Hadju Z, Nicolussi, S, Rau, M, et al. J Nat Prod. 2014;77:1663‒1669. Qin XJ, Yan H, Ni W, et al. Sci Rep. 2016;6:32748. (a) Qin XJ, Lunga PK, Zhao YL, et al. Fitoterapia. 2014; 92:238‒243; (b) Zhang HX, Lunga PK, Li ZJ, Dai Q, Du ZZ. Fitoterapia. 2014;95:147‒153.
References 1.
(a) Marton J, Enisz J, Hosztafi S, Timar T. J Agric Food Chem. 1993;41:148–152; (b) Wang CK, Zhao QJ, Vargas M, et al. J Med Chem. 2016;59:10705–10718;
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4
Tetrahedron Letters
Highlights
Macahydantoins
A
and
B,
two
novel
thiohydantoin derivatives, were isolated from Lepidium meyenii.
Stereochemistries were determined by ECD calculation.
The chemical synthesis of macahydantoin A was achieved.
S0040-4039(17)30335-0 http://dx.doi.org/10.1016/j.tetlet.2017.03.038 TETL 48739
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
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Graphical Abstract
Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepidium meyenii): structural elucidation and concise synthesis of macahydantoin A
Leave this area blank for abstract info.
Mu-Yuan Yu, Xu-Jie Qin, Li-Dong Shao, Xing-Rong Peng, Lei Li, Han Yang, and Ming-Hua Qiu*
1
Tetrahedron Letters j o ur n al h om e p a g e : w w w . e l s e v i er . c o m
Macahydantoins A and B, two new thiohydantoin derivatives from Maca (Lepidium meyenii): structural elucidation and concise synthesis of macahydantoin A Mu-Yuan Yu a, b, c, 1, Xu-Jie Qin a, c, 1, Li-Dong Shao a, c, 1, Xing-Rong Peng a, c, Lei Li a, b, c, Han Yang a, c, and Ming-Hua Qiu 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
A R T IC LE IN F O
A B S TR A C T
Art icle history: Received Received in revised form Accepted Available online
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.
Keywords: Cruciferae 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, and antischistosomal effects.1 Since the first hydantoin was reported in 1861,2 hydantoins and their derivatives have attracted great interest from the synthetic and pharmacological communications.3 However, hydantoin derivatives have not been 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 symptoms.4 In recent years, maca has been popularly cultivated in Lijiang and Dali regions of China for its neuroprotective4,5 and improve cognitive properties.6 A phytochemical investigation of 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. Macahydantoin A (1)7 was isolated as a light yellow oil. Its molecular formula was assigned as C14H16ON2S by its molecular
———
2017 Elsevier Ltd. All rights reserved.
Fig. 1. Chemical structures of 1 and 2.
ion peak at m/z 261.1058 [M+H]+ (calcd for C14H17ON2S, 261.1056) in HRESIMS and 13C NMR spectrum, implying eight degrees of unsaturation. With the aid of the HSQC spectrum, the 13 C NMR data of 1 showed the signals for one monosubstituted aromatic ring [δC 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 δC 171.9 (s, C-3) and a sulfourea carbonyl at δC 192.9 (s, C-1), as well as five methylenes and one methine were observed in its 13C NMR spectrum. These data accounted for six degrees of unsaturation, and the remaining two ones indicated the twocyclic nature of the molecule. The HMBC correlations of δH 5.67 and 5.30 (H2-1a) with C-3a, C-7a, C-1, and C-3 verified that the benzyl unit was connected with N-2. Similarly, HMBC correlations of δH 4.41 (H-7a) with δC 49.8 (t, C-9) and C-1, of δH 1.99 (H-5b) with C-3, and of δH 3.16 (H-9b) with C-1 and C-3,
∗ 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: [email protected] (M.-H. Qiu). 1 These authors contributed equally to this work.
2
Tetrahedron Letters
combined with the substructural fragment of H2-9–H-4–H2-5– H2-6–H2-6 revealed by the 1H–1H COSY spectrum proved the construction of two six-numbers rings. Thus, the planar structure of 1 was established. 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.
S N
N
O 1
H-1H COSY HMBC
Fig.2. Key 2D NMR correlations and ECD spectra of 1. Table 1. 1H (600 MHz) and 13C (150 MHz) NMR data of 1 and 2 in CDCl3. No. 1 3 4 5 6 7 9 1a 2a 3a 4a 5a 6a 7a OMe
Macahydantoin A (1) δC δH (mult., J in Hz) 192.9 s 171.9 s 39.6 d 2.82 (1H, br s) 25.6 t a 2.15 (1H, m) b 1.99 (1H, overlapped) 22.0 t a 1.99 (1H, overlapped) b 1.63 (1H, m) 58.3 t a 4.41 (1H, dd, 13.5, 3.5) b 3.49 (1H, m) 49.9 t a 3.58 (1H, br d, 13.0) b 3.16 (1H, br d, 13.1) 47.9 t a 5.67 (1H, d, 14.6) b 5.30 (1H, d, 14.6) 137.2 s 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)
isothiocyanate10 with amino acid, and sulfourea with αdicarbonyl compound. 11 Considering the presence of a bridgedring 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 facilely afforded intermidate 3 by using Alagarsamy’s condition. 12 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), 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and 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 23% from benzylamine.
Macahydantoin B (2) δC δH (mult., J in Hz) 188.1 s 175.6 s 74.8 s 27.8 t a 1.98 (1H, m) b 1.89 (1H, m) 25.4 t 2.13 (2H, m) 48.6 t 63.9 t 45.2 t 137.0 s 113.5 d 159.6 s 113.4 d 129.5 d 120.3 d 55.2 q
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) 6.95 (1H, s) 6.79 (1H, dd, 8.3, 1.7) 7.21 (1H, t, 7.9) 7.00 (1H, d, 7.6) 3.77 (3H, s)
Macahydantoin B (2)8 had the molecular formula of C15H18O3 N2S by its HRESIMS (m/z 307.1111, [M+H]+) and 13C NMR data. Comparison of the 1H and 13C 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 (δH 3.77, δC 55.2) and an oxyquaternary carbon (δC 74.8). In addition, HMBC correlations of δH 3.77 with δC 159.6 (s, C-4a) and of δH 1.98 (H-5a) and 3.70 (H-9b) with δC 74.8 (s, C-4a) suggested that 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. 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 derivatives were synthesized by the reactions of rhodanate9 or
Scheme 1. Total synthesis of macahydantoin A (1).
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 reacted with H2S to furnish macahydantoin A (1); otherwise, further oxidation reaction of it may form macahydantoin B (2). OH
N
R (H or OMe)
O
O
NH2
N
S N
N
N O HO 2
O R [H]
HN
achiral
H2S -H O 2 R
H 1 S
MeO
O N H
i R = H or OMe
Nicotinamide
O
O
N
-H 2O [O ]
N
R
N H ii H
O N
O iii R = H or OMe
[O]
R
O
H
NH HN O ii R = H or OMe
Scheme 2. Hypothetical biogenetic pathways of 1 and 2.
3 Compounds 1 and 2 were tested for their cytotoxicities against five human cancer cells (HL-60, SMMC-7721, A-549, MCF-7, and SW480) using the MTT method.14 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. albicans).15 Among them, only 4 showed moderate antibacterial activity against E. coli with the MIC value of 6.25 µg/mL. 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 were considered as the characteristic components of maca,13 our finding could enrich the diversity of chemical constituents of maca and even natural resource. Moreover, an efficient total synthesis macahydantoins A (1) was accomplished from commonly available original materials. Although preliminary cytotoxicity screenings revealed they were inactive, the other bioactivies of these sulphur-containing alkaloids should further investigated.
7.
(c) Sundaram, G. S. M.; Venkatesh, C.; Ila, H. Synlett. 2006, 2, 251–254. Ware E. Chem Rev. 1950;46:403–470. (a) Wenzel AG, Jacobsen EN. J. Am. Chem. Soc. 2002;124: 12964–12965; (b) Lanman BA, Overman LE, Paulini R, White NS. J Am Chem Soc. 2007;129:12896–12900; (c) Spicer JA, Lena G, Lyons DM, et al. J Med Chem. 2013;56:9542–9555; (d) Wu FR, Jiang H, Zheng BS, et al. J Med Chem. 2015;58:6899– 6908. Pino-Figueroa A, Nguyen D, Maher TJ. Ann NY Acad Sci. 2010;1199:77–85. Rubio J, Dang H, Gong M, Liu X, Chen SL. Food. Chem. Toxicol. 2006;6:23–27. Rubio J, Caidas M, Dávila S, Gasco M, Gonzales GF. BMC Complement Altern Med. 2006;6:23. 23 Macahydantoin A (1): light yellow oil; [α] D +3.2 (c 0.03, MeOH);
8.
[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 cm−1 ; 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 −1.3) nm for (–)-1; 1 H (CDCl3 , 600 MHz) and 13C (CDCl 3, 150 MHz) NMR data, see Table 1; HRESIMS m/z 261.1058 [M+H]+ (calcd for C14 H17 ON2S, 261.1056). 23 Macahydantoin B (2): light yellow oil; [α] D +2.9 (c 0.08, MeOH);
2. 3.
4. 5. 6.
Acknowledgements 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 Biotech Company) for financial support and the Spectrum Analysis Centre of Kunming Institute of Botany, Chinese Academy of Sciences for the measurements of spectroscopic data.
9.
10. 11. 12. 13.
Supplementary Material 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.
14. 15.
23
23
23
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), 273 (3.62) nm; IR (KBr) νmax: 3431, 2925, 1747, 1430, 1227 cm−1; 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 −11.4) nm for (–)-2; 1H (CDCl 3, 600 MHz) and 13C (CDCl 3, 150 MHz) NMR data, see Table 1; HRESIMS m/z 307.1127 [M+H]+ (calcd for C15 H19 O3 N2 S, 307.1111). (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. Iwata T, Mitoma H, Yamaguchi M. Anal Chim Acta. 2000;416: 69‒75. Tompkins JE. J Med Chem. 1986;29:855–859. Alagarsamy V, Solomon VR, Murugan, M. Bioorg Med Chem. 2007;15:4009‒4015. (a) Zhao JP, Muhammad I, Dunbar DC, Mustafa J, Khah IA. J Agric Food Chem. 2005;53:690‒693; (b) Chain, F E, Grau A, Martins J C, Catalan CAN. Phytochemistry Lett. 2014;8:145‒148; (c) Hadju Z, Nicolussi, S, Rau, M, et al. J Nat Prod. 2014;77:1663‒1669. Qin XJ, Yan H, Ni W, et al. Sci Rep. 2016;6:32748. (a) Qin XJ, Lunga PK, Zhao YL, et al. Fitoterapia. 2014; 92:238‒243; (b) Zhang HX, Lunga PK, Li ZJ, Dai Q, Du ZZ. Fitoterapia. 2014;95:147‒153.
References 1.
(a) Marton J, Enisz J, Hosztafi S, Timar T. J Agric Food Chem. 1993;41:148–152; (b) Wang CK, Zhao QJ, Vargas M, et al. J Med Chem. 2016;59:10705–10718;
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4
Tetrahedron Letters
Highlights
Macahydantoins
A
and
B,
two
novel
thiohydantoin derivatives, were isolated from Lepidium meyenii.
Stereochemistries were determined by ECD calculation.
The chemical synthesis of macahydantoin A was achieved.