CC BY-ND-NC 4.0 · Synlett 2018; 29(09): 1229-1231
DOI: 10.1055/s-0036-1591556
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Copyright with the author

Synthesis of Nepetoidin B

Vitaliy Timokhin
a  Department of Energy Great Lakes Bioenergy Research Center and Department of Biochemistry, the Wisconsin Energy Institute, University of Wisconsin, Madison, WI, 53726, USA   Email: [email protected]
,
a  Department of Energy Great Lakes Bioenergy Research Center and Department of Biochemistry, the Wisconsin Energy Institute, University of Wisconsin, Madison, WI, 53726, USA   Email: [email protected]
,
Yukiko Tsuji
a  Department of Energy Great Lakes Bioenergy Research Center and Department of Biochemistry, the Wisconsin Energy Institute, University of Wisconsin, Madison, WI, 53726, USA   Email: [email protected]
,
John Grabber
b  U.S. Dairy Forage Research Center, USDA-ARS, 1925 Linden Drive West, Madison, WI, 53706, USA
,
John Ralph*
a  Department of Energy Great Lakes Bioenergy Research Center and Department of Biochemistry, the Wisconsin Energy Institute, University of Wisconsin, Madison, WI, 53726, USA   Email: [email protected]
› Author Affiliations
The project was funded by Stanford University’s Global Climate and Energy Program (GCEP), with analytical facilities (primarily NMR) funded in part by the DOE Great Lakes Bioenergy Research Center (DOE Office of Science BER DE-FC02-07ER64494).
Further Information

Publication History

Received: 16 February 2018

Accepted after revision: 26 February 2018

Publication Date:
28 March 2018 (online)

 


Abstract

The first synthesis of nepetoidin B in an overall yield of 17% was achieved in two steps through Baeyer–Villiger oxidation of commercially available 1,5-bis(3,4-dimethoxyphenyl)-1,4-pentadien-3-one with oxone to produce the tetramethylated nepetoidin B, followed by demethylation using boron tribromide.


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Nepetoidin B (1) was initially isolated from Plectranthus caninus in 1975 as the (Z,E)-1 isomer (Figure [1]).[1] Since then, (Z,E)- 1 and its corresponding stereoisomer, (E,E)-1, have been isolated from a variety of plant species using solvent extraction and chromatographic purification.[2–31]. The amounts of (Z,E)-1 and (E,E)-1 vary from 9:1 to 1:1 in different plants,[1] [10] where the stereochemistry of the two isomers has historically been elucidated based on the analyses of J-coupling constants from NMR spectroscopic data.[1] [2] [3] [4] [5] [6] [7] [8] [9] [12] [15] [16] [17] [18] [19] [20]

Nepetoidin’s level in plants is rather low; in a recent isolation from 100 kg of Salvia miltiorrhiza Bunge (Danshen), extraction and purification yielded just 37 mg.[27] Based on the genes, enzymes, and metabolites that have been associated with nepetoidin B, several mechanisms have been proposed for its biosynthesis: (1) condensation of the enol form of dopaldehyde with caffeic acid;[1] [5] [15] [19] (2) oxidative decarboxylation of rosmarinic acid, from which stereo­specific loss of the pro-R or pro-S methylene proton during this process would result in the formation of (Z,E)-1 or (E,E)-1;[21] [25] and (3) decarboxylation of p-hydroxyphenyl­pyruvic acid and subsequent esterification with the enol form of 3,4-dihydroxyphenylacetaldehyde.[25]

Several studies have demonstrated potential biological applications for 1: it has shown antibacterial, antifungal, and free-radical scavenging properties, and it could be used as a chemotaxonomic marker.[8] [9] [10] [12] [15] [30] [31] Furthermore, 1 is an inhibitor of xanthine oxidase and thus could help to regulate hyperuricemia in human gout,[12] as well as inhibit the production of nitric oxide, which is stimulated by bacterial lipopolysaccharide.[27] Surprisingly, in spite of its medicinal characteristics, there has been no reported synthesis of 1 to date. The commercial price of nepetoidin B varies from about $150/mg to about $5,000/g, a price prohibitive to its use in research studies. In continuation of our work on the production of bioproducts from biomass, especially with regard to nepetoidin B and its potential incorporation into lignin in plant cell walls, we sought to design a synthetic route for its production.[32]

Zoom Image
Figure 1 The two naturally occurring isomers of nepetoidin B, (Z,E)-1 and (E,E)-1, isolated from plants

Herein, we report the first synthesis of nepetoidin B. Our synthetic route (Scheme [1]) began with Baeyer–Villiger oxidation of commercially available 1,5-bis(3,4-dimethoxyphenyl)-1,4-pentadien-3-one (2) with oxone, based on a reported procedure for the transformation of α,β-unsaturated ketones into their corresponding vinyl acetates.[33] We optimized the reaction conditions for the stereospecific transformation of only one of the two symmetrical α,β-unsaturated ketones into its corresponding vinyl acetate; our final conditions afforded tetramethylated nepetoidin B [(E,E)-3 isomer] in an isolated yield of 40% from 2, with the starting material being recovered in an isolated yield of 37% (i.e., the overall conversion of starting material to product was about 63%). It is interesting to note that we did not observe iso­merization of (E,E)-3 to (Z,E)-3 during the Baeyer–Villiger oxidation of 2. After optimizing the demethylation of 3 ­using boron tribromide, we obtained 1 in an isolated yield of 43%, thus completing our two-step synthesis of nepetoidin B in an overall yield of 17% (33% when the recovery of starting compound 2 is taken into account).

Zoom Image
Scheme 1 Synthesis of nepetoidin B

Synthetic nepetoidin B was obtained as a mixture of the two isomers in a ratio of 94:6 (E,E)-1/(Z,E)-1 (as estimated by 1H NMR analysis; Figures S1 and S2 in the Supporting ­Information). Considering that the (E,E)-1 isomer was the predominant product in our synthesis, it appears to be the thermodynamically favored isomer. The mixture of the isomers of nepetoidin B [(E,E)-1 94% and (Z,E)-1 6%] was separated by HPLC.[34]

In conclusion, we have described the first synthesis of nepetoidin B. Currently, commercial sources charge about $5,000/g for the product, and so we expect that this convenient synthesis could allow for nepetoidin B to be manufactured at a significantly reduced cost of about $500/g. Its ­potential value as a medicinal compound would seem to make this a worthwhile venture.


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Acknowledgment

The authors are grateful to Justin Mobley for discussion regarding the Baeyer–Villiger oxidation conditions and Steven D. Karlen for help in separating the isomers of nepetoidin B.

Supporting Information

  • References and Notes

  • 1 Arihara S. Ruedi P. Eugster CH. Helv. Chim. Acta 1975; 58: 447
  • 2 Zhang P. Gao ZP. Gao YJ. Xiao L. Chen RY. Kang J. Zhong Yao Cai 2016; 39: 78
  • 3 Zhong JD. Feng F. Li HZ. Li RT. Journal of Kunming University of Science and Technology (Natural Science Edition) 2013; 38: 75
  • 4 Fraga BM. Gonzalez-Coloma A. Alegre-Gomez S. Lopez-Rodriguez M. Amador LJ. Diaz CE. Phytochemistry 2017; 133: 59
  • 5 Nakanishi T. Nishi M. Inada A. Obata H. Tanabe N. Abe S. Wakashiro M. Chem. Pharm. Bull. 1990; 38: 1772
  • 6 Zhong JD. Feng Y. Li HM. Xia XS. Li RT. Nat. Prod. Res. 2016; 30: 2278
  • 7 Huang ZY. Huang B. Xiao CJ. Dong X. Jiang B. Nat. Prod. Res. 2015; 29: 628
  • 8 Zhou W. Xie H. Xu X. Liang Y. Wei X. J. Funct. Foods 2014; 6: 492
  • 9 Tsai SF. Lee SS. Phytochemistry 2014; 101: 121
  • 10 Banthorpe DV. Bilyard HJ. Watson DG. Phytochemistry 1985; 24: 2677
  • 11 Kubínová R. Svajdlenka E. Schneiderová K. Hanáková Z. Dall’Acqua S. Farsa O. Biochem. Syst. Ecol. 2013; 49: 39
  • 12 Grayer RJ. Eckert MR. Veitch NC. Kite GC. Marin PD. Kokubun T. Simmonds MS. J. Paton AJ. Phytochemistry 2003; 64: 519
  • 13 Wang GC. Li T. Deng FY. Li YL. Ye WC. Bioorg. Med. Chem. Lett. 2013; 23: 1379
  • 14 Li M. Xu L. Li Z. Qian S. Qin M. Biochem. Syst. Ecol. 2013; 49: 144
  • 15 Banthorpe DV. Bilyard HJ. Brown GD. Phytochemistry 1989; 28: 2109
  • 16 Falcao RA. do Nascimento PL. A. de Souza SA. da Silva TM. G. de Queiroz AC. da Matta CB. B. Moreira MS. A. Camara CA. Silva TM. S. Evid. Based Complementary Altern. Med. 2013; ID 460613
  • 17 Murata T. Miyase T. Yoshizaki F. J. Nat. Med. 2011; 65: 385
  • 18 Shirota O. Nagamatsu K. Sekita S. J. Nat. Prod. 2006; 69: 1782
  • 19 Brown GD. Banthorpe DV. Characteristic Secondary Meta­bolism in Tissue Cultures of the Labiatae: Two New Chemotaxonomic Markers . In Advances in Labiate Science . Harley RM. Reynolds T. Atkins S. Royal Botanic Gardens; Kew: 1992: 367
  • 20 Wakashiro M. Abe S. Tanabe N. Obata H. Eur. Pat 0 429 038 A2, 1990
  • 21 Dai J. Sorribas A. Yoshida WY. Williams PG. Phytochemistry 2010; 71: 2168
  • 22 Prisinzano TE. Rothman RB. Chem. Rev. 2008; 108: 1732
  • 23 Sevindik HG. Ozgen U. Atila A. Er HO. Kazaz C. Duman H. Chem. Pharm. Bull. 2015; 63: 720
  • 24 Hanson JR. Sci. Progr. 2010; 93: 171
  • 25 Sumaryono W. Proksch P. Hartmann T. Nimtz M. Wray V. Phytochemistry 1991; 30: 3267
  • 26 Formisano C. Rigano D. Senatore F. Chem. Biodivers. 2011; 8: 1783
  • 27 Wu X. Gao H. Sun W. Yu J. Hu H. Xu Q. Chen X. Phytother. Res. 2017; 31: 1072
  • 28 Odonbayar B. Murata T. Matsumoto N. Batkhuu J. Sasaki K. Mongolian Journal of Chemistry 2016; 17: 14
  • 29 Venuprasad MP. Kandikattu HK. Razack S. Amruta N. Khanum F. Biomed. Pharmacother. 2017; 91: 1
  • 30 Beladjila KA. Cotugno R. Berrehal D. Kabouche Z. De Tommasi N. Braca A. De Leo M. Nat. Prod. Res. 2017; 20: 1
  • 31 Süntar I. Nabavi SM. Barreca D. Fischer N. Efferth T. Phytother. Res. 2018; 32: 185
  • 32 Rinaldi R. Jastrzebshi R. Clough MT. Ralph J. Kennema M. Bruijnincx PC. A. Weckhuysen BM. Angew. Chem. Int. Ed. 2016; 55: 8164
  • 33 Poladura B. Martinez-Castaneda A. Rodriguez-Solla H. Llavona R. Concellon C. del Amo V. Org. Lett. 2013; 15: 2810
  • 34 Synthesis of 2-(3,4-Dihydroxyphenyl)ethenyl-3-(3,4-dihydroxyphenyl)-2-propenoate (1) To a stirred solution of (E,E)-3 (1.341 g, 3.620 mmol, 1.0 equiv) in dry CH2Cl2 (20 mL) under argon was added neat BBr3 (2.09 mL, 21.722 mmol, 6.0 equiv) dropwise at −78 °C. The solution was stirred at the same temperature for another 30 min, at which point the mixture was allowed to warm to 0 °C over the course of 1 h, and then to warm to r.t. over the course of 1 h. After once again cooling the mixture to −78 °C, it was quenched by addition of saturated aqueous NaHCO3 (18 mL) and then allowed to warm to r.t. over 20 min. The mixture was partitioned between EtOAc (120 mL) and H2O (150 mL), and the aqueous layer was extracted with EtOAc (2 x 50 mL). The combined organic layers were washed with brine (50 mL), then dried over anhydrous Na2SO4, and the solution was concentrated in vacuo. The residue was purified by flash column chromatography on silica gel (MeOH/CH2Cl2 10:90) to furnish nepetoidin B, compound 1, as a yellow solid (490 mg, 43%). Rf = 0.58 (MeOH/CH2Cl2 15:85). The ratio of isomers (E,E)-1/(Z,E)-1 is 94:6, as determined by 1H NMR spectroscopic analysis (signals at 5.67 (d, J = 7.4 Hz, H-7) and 6.36 (d, J = 15.8 Hz, H-8) for the (Z,E)-1 and (E,E)-1 isomers, respectively). HPLC Separation of the Isomers of Nepetoidin B [(E,E)-1 and (Z,E)-1] The mixture of the isomers of nepetoidin B [(E,E)-1 94% and (Z,E)-1 6%] obtained from the demethylation of (E,E)-3 was separated by HPLC. To collect a sufficient quantity for 1H and 13C NMR analysis, 1 (12 mg) was dissolved in MeOH (350 μL), and the method described above was run five times using 50 μL injections of the solution. The appropriate fractions were combined and concentrated in vacuo to afford each purified isomer for further analysis. (E,E)-1 (7 mg): 1H NMR (500 MHz, acetone-d 6): δH = 6.36 (d, J = 15.8 Hz, H-8), 6.38 (d, J = 12.8 Hz, H-7'), 6.77−6.78 (m, H-6' and H-5), 6.89 (d, J = 8.2 Hz, H-5'), 6.93 (d, J = 1.8 Hz, H-2), 7.11 (dd, J = 8.2, 2.1 Hz, H-6), 7.22 (d, J = 2.1 Hz, H-2'), 7.68 (d, J = 15.9 Hz, H-7), 7.81 (d, J = 12.8 Hz, H-8'), 8.21 (br. s, 4 x OH). The obtained NMR spectroscopic data for (E,E)-1 matched literature values.10,15,19 (Z,E)-1 (0.3 mg): 1H NMR (500 MHz, acetone-d 6): δH = 5.67 (d, J = 7.4 Hz, H-7'), 6.51 (d, J = 15.9 Hz, H-8), 6.81 (d, J = 8.2 Hz, H-5'), 6.90 (d, J = 8.2 Hz, H-5), 7.00 (dd, J = 8.2, 2.1 Hz, H-6'), 7.13 (dd, J = 8.2, 2.1 Hz, H-6), 7.26 (d, J = 2.0 Hz, H-2), 7.26 (d, J = 7.3 Hz, H-8'), 7.37 (d, J = 2.1 Hz, H-2'), 7.73 (d, J = 15.9 Hz, H-7), 8.05 (br. s, 4 x OH).1,10,15,19,30

  • References and Notes

  • 1 Arihara S. Ruedi P. Eugster CH. Helv. Chim. Acta 1975; 58: 447
  • 2 Zhang P. Gao ZP. Gao YJ. Xiao L. Chen RY. Kang J. Zhong Yao Cai 2016; 39: 78
  • 3 Zhong JD. Feng F. Li HZ. Li RT. Journal of Kunming University of Science and Technology (Natural Science Edition) 2013; 38: 75
  • 4 Fraga BM. Gonzalez-Coloma A. Alegre-Gomez S. Lopez-Rodriguez M. Amador LJ. Diaz CE. Phytochemistry 2017; 133: 59
  • 5 Nakanishi T. Nishi M. Inada A. Obata H. Tanabe N. Abe S. Wakashiro M. Chem. Pharm. Bull. 1990; 38: 1772
  • 6 Zhong JD. Feng Y. Li HM. Xia XS. Li RT. Nat. Prod. Res. 2016; 30: 2278
  • 7 Huang ZY. Huang B. Xiao CJ. Dong X. Jiang B. Nat. Prod. Res. 2015; 29: 628
  • 8 Zhou W. Xie H. Xu X. Liang Y. Wei X. J. Funct. Foods 2014; 6: 492
  • 9 Tsai SF. Lee SS. Phytochemistry 2014; 101: 121
  • 10 Banthorpe DV. Bilyard HJ. Watson DG. Phytochemistry 1985; 24: 2677
  • 11 Kubínová R. Svajdlenka E. Schneiderová K. Hanáková Z. Dall’Acqua S. Farsa O. Biochem. Syst. Ecol. 2013; 49: 39
  • 12 Grayer RJ. Eckert MR. Veitch NC. Kite GC. Marin PD. Kokubun T. Simmonds MS. J. Paton AJ. Phytochemistry 2003; 64: 519
  • 13 Wang GC. Li T. Deng FY. Li YL. Ye WC. Bioorg. Med. Chem. Lett. 2013; 23: 1379
  • 14 Li M. Xu L. Li Z. Qian S. Qin M. Biochem. Syst. Ecol. 2013; 49: 144
  • 15 Banthorpe DV. Bilyard HJ. Brown GD. Phytochemistry 1989; 28: 2109
  • 16 Falcao RA. do Nascimento PL. A. de Souza SA. da Silva TM. G. de Queiroz AC. da Matta CB. B. Moreira MS. A. Camara CA. Silva TM. S. Evid. Based Complementary Altern. Med. 2013; ID 460613
  • 17 Murata T. Miyase T. Yoshizaki F. J. Nat. Med. 2011; 65: 385
  • 18 Shirota O. Nagamatsu K. Sekita S. J. Nat. Prod. 2006; 69: 1782
  • 19 Brown GD. Banthorpe DV. Characteristic Secondary Meta­bolism in Tissue Cultures of the Labiatae: Two New Chemotaxonomic Markers . In Advances in Labiate Science . Harley RM. Reynolds T. Atkins S. Royal Botanic Gardens; Kew: 1992: 367
  • 20 Wakashiro M. Abe S. Tanabe N. Obata H. Eur. Pat 0 429 038 A2, 1990
  • 21 Dai J. Sorribas A. Yoshida WY. Williams PG. Phytochemistry 2010; 71: 2168
  • 22 Prisinzano TE. Rothman RB. Chem. Rev. 2008; 108: 1732
  • 23 Sevindik HG. Ozgen U. Atila A. Er HO. Kazaz C. Duman H. Chem. Pharm. Bull. 2015; 63: 720
  • 24 Hanson JR. Sci. Progr. 2010; 93: 171
  • 25 Sumaryono W. Proksch P. Hartmann T. Nimtz M. Wray V. Phytochemistry 1991; 30: 3267
  • 26 Formisano C. Rigano D. Senatore F. Chem. Biodivers. 2011; 8: 1783
  • 27 Wu X. Gao H. Sun W. Yu J. Hu H. Xu Q. Chen X. Phytother. Res. 2017; 31: 1072
  • 28 Odonbayar B. Murata T. Matsumoto N. Batkhuu J. Sasaki K. Mongolian Journal of Chemistry 2016; 17: 14
  • 29 Venuprasad MP. Kandikattu HK. Razack S. Amruta N. Khanum F. Biomed. Pharmacother. 2017; 91: 1
  • 30 Beladjila KA. Cotugno R. Berrehal D. Kabouche Z. De Tommasi N. Braca A. De Leo M. Nat. Prod. Res. 2017; 20: 1
  • 31 Süntar I. Nabavi SM. Barreca D. Fischer N. Efferth T. Phytother. Res. 2018; 32: 185
  • 32 Rinaldi R. Jastrzebshi R. Clough MT. Ralph J. Kennema M. Bruijnincx PC. A. Weckhuysen BM. Angew. Chem. Int. Ed. 2016; 55: 8164
  • 33 Poladura B. Martinez-Castaneda A. Rodriguez-Solla H. Llavona R. Concellon C. del Amo V. Org. Lett. 2013; 15: 2810
  • 34 Synthesis of 2-(3,4-Dihydroxyphenyl)ethenyl-3-(3,4-dihydroxyphenyl)-2-propenoate (1) To a stirred solution of (E,E)-3 (1.341 g, 3.620 mmol, 1.0 equiv) in dry CH2Cl2 (20 mL) under argon was added neat BBr3 (2.09 mL, 21.722 mmol, 6.0 equiv) dropwise at −78 °C. The solution was stirred at the same temperature for another 30 min, at which point the mixture was allowed to warm to 0 °C over the course of 1 h, and then to warm to r.t. over the course of 1 h. After once again cooling the mixture to −78 °C, it was quenched by addition of saturated aqueous NaHCO3 (18 mL) and then allowed to warm to r.t. over 20 min. The mixture was partitioned between EtOAc (120 mL) and H2O (150 mL), and the aqueous layer was extracted with EtOAc (2 x 50 mL). The combined organic layers were washed with brine (50 mL), then dried over anhydrous Na2SO4, and the solution was concentrated in vacuo. The residue was purified by flash column chromatography on silica gel (MeOH/CH2Cl2 10:90) to furnish nepetoidin B, compound 1, as a yellow solid (490 mg, 43%). Rf = 0.58 (MeOH/CH2Cl2 15:85). The ratio of isomers (E,E)-1/(Z,E)-1 is 94:6, as determined by 1H NMR spectroscopic analysis (signals at 5.67 (d, J = 7.4 Hz, H-7) and 6.36 (d, J = 15.8 Hz, H-8) for the (Z,E)-1 and (E,E)-1 isomers, respectively). HPLC Separation of the Isomers of Nepetoidin B [(E,E)-1 and (Z,E)-1] The mixture of the isomers of nepetoidin B [(E,E)-1 94% and (Z,E)-1 6%] obtained from the demethylation of (E,E)-3 was separated by HPLC. To collect a sufficient quantity for 1H and 13C NMR analysis, 1 (12 mg) was dissolved in MeOH (350 μL), and the method described above was run five times using 50 μL injections of the solution. The appropriate fractions were combined and concentrated in vacuo to afford each purified isomer for further analysis. (E,E)-1 (7 mg): 1H NMR (500 MHz, acetone-d 6): δH = 6.36 (d, J = 15.8 Hz, H-8), 6.38 (d, J = 12.8 Hz, H-7'), 6.77−6.78 (m, H-6' and H-5), 6.89 (d, J = 8.2 Hz, H-5'), 6.93 (d, J = 1.8 Hz, H-2), 7.11 (dd, J = 8.2, 2.1 Hz, H-6), 7.22 (d, J = 2.1 Hz, H-2'), 7.68 (d, J = 15.9 Hz, H-7), 7.81 (d, J = 12.8 Hz, H-8'), 8.21 (br. s, 4 x OH). The obtained NMR spectroscopic data for (E,E)-1 matched literature values.10,15,19 (Z,E)-1 (0.3 mg): 1H NMR (500 MHz, acetone-d 6): δH = 5.67 (d, J = 7.4 Hz, H-7'), 6.51 (d, J = 15.9 Hz, H-8), 6.81 (d, J = 8.2 Hz, H-5'), 6.90 (d, J = 8.2 Hz, H-5), 7.00 (dd, J = 8.2, 2.1 Hz, H-6'), 7.13 (dd, J = 8.2, 2.1 Hz, H-6), 7.26 (d, J = 2.0 Hz, H-2), 7.26 (d, J = 7.3 Hz, H-8'), 7.37 (d, J = 2.1 Hz, H-2'), 7.73 (d, J = 15.9 Hz, H-7), 8.05 (br. s, 4 x OH).1,10,15,19,30

Zoom Image
Figure 1 The two naturally occurring isomers of nepetoidin B, (Z,E)-1 and (E,E)-1, isolated from plants
Zoom Image
Scheme 1 Synthesis of nepetoidin B