Naturally Occurring Diterpenoid Dimers: Source, Biosynthesis, Chemistry and Bioactivities

Abstract

Diterpenoid dimers are rare in nature and mainly found in higher plants including the families Acanthaceae, Annonaceae, Asteraceae, Calceolariaceae, Chrysobalanaceae, Cupressaceae, Euphorbiaceae, Fabaceae, Lamiaceae, Liliaceae, Meliaceae, Rhizophoraceae, Taxaceae, Velloziaceae, and Zingiberaceae. In addition, a few diterpenoid dimers have been also reported from fungi (Psathyrellaceae), liverworts (Scapaniaceae), and a gorgonian (Gorgoniidae). They feature a wide variety of structures due to different core skeletons, linkage patterns, substituents, and configurations. Accordingly, diterpenoid dimers exhibit a broad range of bioactivities, including cytotoxic, anti-inflammatory, antimicrobial, antimalarial, and antifouling properties, which have attracted more and more research interests in the past decades. This review with 176 metabolites from 109 references provides a comprehensive and up-to-date overview of the source, biosynthesis, structure, synthesis, and bioactivities of diterpenoid dimers.

Key words

diterpenoid dimers - structure - source - biosynthesis - synthesis - bioactivities

• References

• 1 Hanson JR. Diterpenoids of terrestrial origin. Nat Prod Rep 2015; 32: 1654-1663
• 2 Vasas A, Hohmann J. Euphorbia diterpenes: isolation, structure, biological activity, and synthesis (2008–2012). Chem Rev 2014; 114: 8579-8612
• 3 Gonzalez MA. Aromatic abietane diterpenoids: their biological activity and synthesis. Nat Prod Rep 2015; 32: 684-704
• 4 Cragg GM. Paclitaxel (Taxol): a success story with valuable lessons for natural product drug discovery and development. Med Res Rev 1998; 18: 315-331
• 5 Siebert DJ. Salvia divinorum and salvinorin A: new pharmacologic findings. J Ethnopharmacol 1994; 43: 53-56
• 6 Roth BL, Baner K, Westkaemper R, Siebert D, Rice KC, Steinberg S, Ernsberger P, Rothman RB. Salvinorin A: a potent naturally occurring nonnitrogenous kappa opioid selective agonist. Proc Natl Acad Sci U S A 2002; 99: 11934-11939
• 7 Liu J, He XF, Wang GH, Merino EF, Yang SP, Zhu RX, Gan LS, Zhang H, Cassera MB, Wang HY, Kingston DG, Yue JM. Aphadilactones A–D, four diterpenoid dimers with DGAT inhibitory and antimalarial activities from a Meliaceae plant. J Org Chem 2014; 79: 599-607
• 8 Zhang HJ, Zhang YM, Luo JG, Luo J, Kong LY. Anti-inflammatory diterpene dimers from the root barks of Aphanamixis grandifolia . Org Biomol Chem 2015; 13: 7452-7458
• 9 Zhang H, Liu J, Gan LS, Dalal S, Cassera MB, Yue JM. Antimalarial diterpenoid dimers of a new carbon skeleton from Aphanamixis grandifolia . Org Biomol Chem 2016; 14: 957-962
• 10 Wang WX, Zhu JJ, Zou YK, Hong ZL, Liu ST, Li M, Huang Y, Xiong J, Zhao Y, Yang GX, Xia G, Hu JF. Trichotomone, a new cytotoxic dimeric abietane-derived diterpene from Clerodendrum trichotomum . Tetrahedron Lett 2013; 54: 2549-2552
• 11 Zhang JY, Abdel-Mageed WM, Liu MM, Huang P, He WN, Li L, Song FH, Dai HQ, Liu XT, Liang JY, Zhang LX. Caesanines A–D, new cassane diterpenes with unprecedented N bridge from Caesalpinia sappan . Org Lett 2013; 15: 4726-4729
• 12 Zi J, Mafu S, Peters RJ. To gibberellins and beyond! Surveying the evolution of (di)terpenoid metabolism. Annu Rev Plant Biol 2014; 65: 259-286
• 13 Yin JP, Gu M, Li Y, Nan FJ. Total synthesis of aphadilactones A–D. J Org Chem 2014; 79: 6294-6301
• 14 Oikawa H, Tokiwano T. Enzymatic catalysis of the Diels-Alder reaction in the biosynthesis of natural products. Nat Prod Rep 2004; 21: 321-352
• 15 Oikawa H, Katayama K, Suzuki Y, Ichihara A. Enzymatic-activity catalyzing exo-selective Diels-Alder reaction in solanapyrone biosynthesis. Chem Commun 1995; 1321-1322
• 16 Katayama K, Kobayashi T, Oikawa H, Honma M, Ichihara A. Enzymatic activity and partial purification of solanapyrone synthase: first enzyme catalyzing Diels-Alder reaction. Biochim Biophys Acta 1998; 1384: 387-395
• 17 Auclair K, Sutherland A, Kennedy J, Witter DJ, Van den Heever JP, Hutchinson CR, Vederas JC. Lovastatin nonaketide synthase catalyzes an intramolecular Diels-Alder reaction of a substrate analogue. J Am Chem Soc 2000; 122: 11519-11520
• 18 Ose T, Watanabe K, Mie T, Honma M, Watanabe H, Yao M, Oikawa H, Tanaka I. Insight into a natural Diels-Alder reaction from the structure of macrophomate synthase. Nature 2003; 422: 185-189
• 19 Xu JA, Deng QL, Chen JG, Houk KN, Bartek J, Hilvert D, Wilson IA. Evolution of shape complementarity and catalytic efficiency from a primordial antibody template. Science 1999; 286: 2345-2348
• 20 Kim SP, Leach AG, Houk KN. The origins of noncovalent catalysis of intermolecular Diels-Alder reactions by cyclodextrins, self-assembling capsules, antibodies, and RNAses. J Org Chem 2002; 67: 4250-4260
• 21 Siegel JB, Zanghellini A, Lovick HM, Kiss G, Lambert AR, Clair JLS, Gallaher JL, Hilvert D, Gelb MH, Stoddard BL, Houk KN, Michael FE, Baker D. Computational design of an enzyme catalyst for a stereoselective bimolecular Diels-Alder reaction. Science 2010; 329: 309-313
• 22 Wu JZ, Ruan HL, Yao NH, Sun HD, Zhao QS, Morizane C, Iida A, Fujita T. Structural elucidation and synthesis of fritillebinide A from bulbs of Fritillaria ebeiensis . Acta Pharm Sin 1999; 34: 600-604
• 23 Zhao Y, Huang SX, Xiao WL, Ding LS, Pu JX, Li X, Yang LB, Sun HD. Diterpenoids from Isodon pharicus . Tetrahedron Lett 2009; 50: 2019-2023
• 24 Matsuda T, Kuroyanagi M, Sugiyama S, Umehara K, Ueno A, Nishi K. Cell differentiation-inducing diterpenes from Andrographis paniculata Nees. Chem Pharm Bull (Tokyo) 1994; 42: 1216-1225
• 25 Hasan CM, Healey TM, Waterman PG. Chemical studies in the Annonaceae .13. acutifloric acid-a diterpene dimer from the stem bark of Xylopia acutiflora . Phytochemistry 1985; 24: 192-194
• 26 Vilegas W, Felicio JD, Roque NF, Gottlieb HE. Diterpenic adducts from Xylopia Species. Phytochemistry 1991; 30: 1869-1872
• 27 Takahashi JA, Boaventura MAD, Bayma JD, Oliveira AB. Frutoic acid, a dimeric kaurane diterpene from Xylopia frutescens . Phytochemistry 1995; 40: 607-609
• 28 Moreira IC, Roque NF, Lago JHG. Diterpene adducts from branches of Xylopia emarginata . Biochem Syst Ecol 2006; 34: 833-837
• 29 Martins D, Hamerski L, Alvarenga SAV, Roque NF. Labdane dimers from Xylopia aromatica . Phytochemistry 1999; 51: 813-817
• 30 Yang NY, Tian LJ, Meng ZM, Han Y. A new diterpenoid dimer from Annona glabra . Chin Chem Lett 2003; 14: 58-61
• 31 Chen CH, Hsieh TJ, Liu TZ, Chern CL, Hsieh PY, Chen CY. Annoglabayin, a novel dimeric kaurane diterpenoid, and apoptosis in Hep G2 cells of annomontacin from the fruits of Annona glabra . J Nat Prod 2004; 67: 1942-1946
• 32 Labbe C, Castillo M, Hernandez M. Diterpenoids from Baccharis lejia . Phytochemistry 1991; 30: 1607-1611
• 33 Chamy MC, Piovano M, Garbarino JA, Gambaro V, Miranda C. Diterpenoids from Calceolaria species 3. foliosate, a bis-diterpene and 9-epi-ent-7,15-isopimaradiene derivatives from Calceolaria foliosa . Phytochemistry 1989; 28: 571-574
• 34 Piovano M, Chamy MC, Garbarino JA, Gambaro V. Diterpenoids from Calceolaria species 4.9-epi-ent-7,15-isopimaradiene derivatives from Calceolaria glandulosa . Phytochemistry 1989; 28: 2844-2845
• 35 Chamy MC, Piovano M, Garbarino JA, Miranda C, Gambaro V. Diterpenoids from Calceolaria species 5. diterpenes from Calceolaria lepida . Phytochemistry 1990; 29: 2943-2946
• 36 Chamy MC, Piovano M, Garbarino JA, Gambaro V. Diterpenoids from Calceolaria species 10. diterpenes from Calceolaria polifolia . Phytochemistry 1991; 30: 3365-3368
• 37 Silva P, Chamy MC, Piovano M, Garbarino JA. Diterpenoids from Calceolaria petioalaris 14. diterpenoids from Calceolaria species. Phytochemistry 1993; 34: 449-451
• 38 Garbarino JA, Molinari A. Diterpenoids from Calceolaria species 9. labdane diterpenes from Calceolaria densifolia . J Nat Prod 1992; 55: 744-747
• 39 Braca A, Abdel-Razik AF, Mendez J, Morelli I. A new kaurane diterpene dimer from Parinari campestris . Fitoterapia 2005; 76: 614-619
• 40 Hanari N, Yamamoto H, Ooi T, Kusumi T, Kuroda K. A new diterpene dimer from the bark of Chamaecyparis obtusa . J Wood Sci 2001; 47: 36-40
• 41 Arihara S, Umeyama A, Bando S, Imoto S, Ono M, Tani M, Yoshikawa K. A new abietane and two dimeric abietane diterpenes from the black heartwood of Cryptomeria japonica . Chem Pharm Bull (Tokyo) 2004; 52: 354-358
• 42 Hsieh CL, Tseng MH, Kuo YH. Formosadimers A, B, and C from the bark of Calocedrus macrolepis var. formosana . Chem Pharm Bull (Tokyo) 2005; 53: 1463-1465
• 43 Hsieh CL, Shiu LL, Tseng MH, Shao YY, Kuo YH. Calocedimers A, B, C, and D from the bark of Calocedrus macrolepis var. formosana . J Nat Prod 2006; 69: 665-667
• 44 Kuo YH, Yu MT. Diterpenes from the heartwood of Juniperus formosana Hay var concolor Hay. Chem Pharm Bull (Tokyo) 1996; 44: 1431-1435
• 45 Kuo YH, Chen CH, Wein YS. New dimeric monoterpenes and dimeric diterpenes from the heartwood of Chamaecyparis obtusa var. formosana . Helv Chim Acta 2002; 85: 2657-2663
• 46 Hou XF, Yao S, Mandi A, Kurtan T, Tang CP, Ke CQ, Li XQ, Ye Y. Bicunningines A and B, two new dimeric diterpenes from Cunninghamia lanceolata . Org Lett 2012; 14: 460-463
• 47 Lin WH, Fang JM, Cheng YS. Diterpenes and related cycloadducts from Taiwania cryptomerioides . Phytochemistry 1996; 42: 1657-1663
• 48 Lin WH, Fang JM, Cheng YS. Cycloadducts of terpene quinones from Taiwania cryptomerioides . Phytochemistry 1997; 46: 169-173
• 49 Pan ZH, Ning DS, Wu XD, Huang SS, Li DP, Lv SH. New clerodane diterpenoids from the twigs and leaves of Croton euryphyllus . Bioorg Med Chem Lett 2015; 25: 1329-1332
• 50 Thuong PT, Thi HMP, Thi VTL, Dao TT, Dang TT, Nguyen QT, Oh WK. Symmetric dimers of ent-kaurane diterpenoids with cytotoxic activity from Croton tonkinensis . Bioorg Med Chem Lett 2012; 22: 1122-1124
• 51 Fu GM, Qin HL, Yu SS, Yu BY. Yuexiandajisu D, a novel 18-nor-rosane-type dimeric diterpenoid from Euphorbia ebracteolata Hayata. J Asian Nat Prod Res 2006; 8: 29-34
• 52 Zhou TX, Bao GH, Ma QG, Qin GW, Che CT, Lv Y, Wang C, Zheng QT. Langduin C, a novel dimeric diterpenoid from the roots of Euphorbia fischeriana . Tetrahedron Lett 2003; 44: 135-137
• 53 Zhang BY, Wang H, Luo XD, Du ZZ, Shen JW, Wu HF, Zhang XF. Bisyinshanic acids A and B, two novel diterpene dimers from the toots of Euphorbia yinshanica . Helv Chim Acta 2012; 95: 1672-1679
• 54 Tene M, Tane P, Tamokou JD, Kuiate JR, Connolly JD. Degraded diterpenoids from the stem bark of Neoboutonia mannii . Phytochemistry Lett 2008; 1: 120-124
• 55 Tane P, Bergquist KE, Tene M, Ngadjui BT, Ayafor JF, Sterner O. Cyclodione, an unsymmetrical dimeric diterpene from Cylicodiscus gabunensis . Tetrahedron 1995; 51: 11595-11600
• 56 Miyagawa T, Ohtsuki T, Koyano T, Kowithayakorn T, Ishibashi M. Cassaine diterpenoid dimers isolated from Erythrophleum succirubrum with TRAIL-resistance overcoming activity. Tetrahedron Lett 2009; 50: 4658-4662
• 57 Du D, Qu J, Wang JM, Yu SS, Chen XG, Xu S, Ma SG, Li Y, Ding GZ, Fang L. Cytotoxic cassaine diterpenoid-diterpenoid amide dimers and diterpenoid amides from the leaves of Erythrophleum fordii . Phytochemistry 2010; 71: 1749-1755
• 58 Hung TM, Cuong TD, Kim JA, Lee JH, Woo MH, Min BS. In vitro apoptotic effect of cassaine-type diterpene amides from Erythrophleum fordii on PC-3 prostate cancer cells. Bioorg Med Chem Lett 2014; 24: 4989-4994
• 59 Rustaiyan A, Mossleminkupaii MH, Papastergiou F, Jakupovic J. Persianone, a dimeric diterpene from Ballota aucheri . Phytochemistry 1995; 40: 875-879
• 60 Pandey R, Verma RK, Gupta MM. Neo-clerodane diterpenoids from Clerodendrum inerme . Phytochemistry 2005; 66: 643-648
• 61 Shen XY, Isogai A, Furihata K, Sun HD, Suzuki A. Maoecrystal M-a naturally-occurring symmetrical ent-kaurane dimer from Rabdosia eriocalyx . Phytochemistry 1994; 35: 725-729
• 62 Yang JH, Wang WG, Du X, He F, Zhang HB, Li XN, Li Y, Pu JX, Sun HD. Heterodimeric ent-kauranoids from Isodon tenuifolius . J Nat Prod 2014; 77: 2444-2453
• 63 Yang LB, Yang J, Li LM, Lei C, Zhao Y, Huang SX, Xiao WL, Han QB, Pu JX, Sun HD. Symmetric and asymmetric ent-kaurane dimers isolated from Isodon japonicus . Tetrahedron Lett 2008; 49: 3574-3577
• 64 Han QB, Lu Y, Wu L, He ZD, Qiao CF, Xu HX, Zheng QT, Sun HD. An asymmetric ent-kauranoid dimer from Isodon rubescens var. lushanensis . Tetrahedron Lett 2005; 46: 5373-5375
• 65 Huang SX, Xiao WL, Li LM, Li SH, Zhou Y, Ding LS, Lou LG, Sun HD. Bisrubescensins A–C: three new dimeric ent-kauranoids isolated from Isodon rubescens . Org Lett 2006; 8: 1157-1160
• 66 Hong SS, Lee SA, Lee C, Han XH, Choe S, Kim N, Lee D, Lee CK, Kim Y, Hong JT, Lee MK, Hwang BY. Dimeric ent-kaurane diterpenoids from Isodon excisus . J Nat Prod 2011; 74: 2382-2387
• 67 Han QB, Lu Y, Zhang LL, Zheng QT, Sun HD. Novel ent-kaurane dimers from Isodon rubescens var. rubescens . Tetrahedron Lett 2004; 45: 2833-2837
• 68 Han QB, Li RT, Zhang JX, Sun HD. New ent-abietanoids from Isodon rubescens . Helv Chim Acta 2004; 87: 1007-1015
• 69 Huang SX, Pu JX, Xiao WL, Li LM, Weng ZY, Zhou Y, Han QB, Peng SL, Ding LS, Lou LG, Sun HD. ent-Abietane diterpenoids from Isodon rubescens var. rubescens . Phytochemistry 2007; 68: 616-622
• 70 Huang B, Xiao CJ, Huang ZY, Tian XY, Cheng X, Dong X, Jiang B. Hispidanins A–D: four new asymmetric dimeric diterpenoids from the rhizomes of Isodon hispida . Org Lett 2014; 16: 3552-3555
• 71 Marques CG, Pedro M, Simoes MF, Nascimento MS, Pinto MM, Rodriguez B. Effect of abietane diterpenes from Plectranthus grandidentatus on the growth of human cancer cell lines. Planta Med 2002; 68: 839-840
• 72 Suresh G, Babu KS, Rao MSA, Rao VRS, Yadav PA, Nayak VL, Ramakrishna S. Premnalatifolin A, a novel dimeric diterpene from Premna latifolia Roxb. Tetrahedron Lett 2011; 52: 5016-5019
• 73 Salae AW, Boonnak N. Obtusinones D and E, linear and angular fused dimeric icetexane diterpenoids from Premna obtusifolia roots. Tetrahedron Lett 2013; 54: 1356-1359
• 74 Li M, Zhang JS, Chen MQ. A novel dimeric diterpene from Salvia prionitis . J Nat Prod 2001; 64: 971-972
• 75 Xu J, Chang J, Zhao M, Zhang JS. Abietane diterpenoid dimers from the roots of Salvia prionitis . Phytochemistry 2006; 67: 795-799
• 76 Gonzalez AG, Rodriguez CM, Luis JG. Diterpenes from the flowers of Salvia canariensis . Phytochemistry 1987; 26: 1471-1474
• 77 Xiao QL, Xia F, Yang XW, Liao Y, Yang LX, Wei YK, Li X, Xu G. New dimeric and seco-abietane diterpenoids from Salvia wardii . Nat Prod Bioprospect advance online publication 8 April 2015
• 78 Choudhary MI, Hussain A, Ali Z, Adhikari A, Sattar SA, Ayatollahi SA, Al-Majid AM. Diterpenoids including a novel dimeric conjugate from Salvia leriaefolia . Planta Med 2012; 78: 269-275
• 79 Hussain A, Adhikari A, Choudhary MI, Ayatollahi SA. Atta-ur-Rahman. New adduct of abietane-type diterpene from Salvia leriifolia Benth. Nat Prod Res advance online publication 6 January 2016
• 80 Fraga BM, Diaz CE, Lopez-Rodriguez M. Two novel abietane dimers from transformed root cultures of Salvia broussonetii . Tetrahedron Lett 2014; 55: 877-879
• 81 Christensen KB, Jorgensen M, Kotowska D, Petersen RK, Kristiansen K, Christensen LP. Activation of the nuclear receptor PPAR gamma by metabolites isolated from sage (Salvia officinalis L.). J Ethnopharmacol 2010; 132: 127-133
• 82 Bisio A, De Tommasi N, Romussi G. Diterpenoids from Salvia wagneriana . Planta Med 2004; 70: 452-457
• 83 Gao C, Han L, Zheng D, Jin HW, Gai CY, Wang JB, Zhang H, Zhang LR, Fu HZ. Dimeric abietane diterpenoids and sesquiterpenoid lactones from Teucrium viscidum . J Nat Prod 2015; 78: 630-638
• 84 Wu JZ, Morizane C, Iida A, Ueda SI, Zhou ZL, Xu M, Zhang M, Li RM, Fujita T. Structures of three new diterpenoids, fritillebic acid and fritillebins A and B, from bulbs of Fritillaria ebeiensis G. D. Yu et G. Q. Ji. Chem Pharm Bull (Tokyo) 1995; 43: 1448-1453
• 85 Wu JZ, Ruan HL, Zeng CL, Cheng HA, Zhang F, Zhao QS, Sun HD, Fujita T. Structures of two new diterpenoid dimers from bulbs of Fritillaria ebeiensis . J Asian Nat Prod Res 1999; 1: 251-257
• 86 Wu JZ, Wen YP, Ruan HL, Yao NH, Zhao QS, Sun HD, Morizane C, Iida A, Fujita T. Structural elucidations of two ent-kaurane dimers from bulbs of Fritillaria ebeiensis var. purpurea . J Asian Nat Prod Res 2000; 2: 213-218
• 87 Wu JZ, Ruan HL, Yao NH, Zhao QS, Sun HD, Morizane C, Iida A, Fujita T. Structures of two diterpenoid dimers from bulbs of Fritillaria ebeiensis . J Asian Nat Prod Res 2000; 2: 161-167
• 88 Ruan HL, Zhang YH, Wu JZ, Sun HD, Fujita T. Two new diterpenoid dimers, fritillebinide D and E, from bulbs of Fritillaria ebeiensis . J Asian Nat Prod Res 2002; 4: 309-314
• 89 Zhang HJ, Luo J, Shan SM, Wang XB, Luo JG, Yang MH, Kong LY. Aphanamenes A and B, two new acyclic diterpene [4 + 2]-cycloaddition adducts from Aphanamixis grandifolia . Org Lett 2013; 15: 5512-5515
• 90 Zhang Y, Lu Y, Mao L, Proksch P, Lin WH. Tagalsins I and J, two novel tetraterpenoids from the mangrove plant, Ceriops tagal . Org Lett 2005; 7: 3037-3040
• 91 Chen JD, Qiu Y, Yang ZW, Lin P, Lin YM. Dimeric diterpenes from the roots of the mangrove plant Ceriops tagal . Helv Chim Acta 2008; 91: 2292-2298
• 92 Chen JD, Yi RZ, Lin YM, Feng DQ, Zhou HC, Wang ZC. Characterization of terpenoids from the root of Ceriops tagal with antifouling activity. Int J Mol Sci 2011; 12: 6517-6528
• 93 Galli B, Gasparrini F, Lanzotti V, Misiti D, Riccio R, Villani C, He GF, Ma ZW, Yin WF. Grandione, a new heptacyclic dimeric diterpene from Torreya grandis Fort. Tetrahedron 1999; 55: 11385-11394
• 94 Ni ZY, Wu YB, Dong M, Zhang ML, Wang YF, Sauriol F, Huo CH, Shi QW, Gu YC, Kiyota H, Cong B. Diabietane ether, a new dimeric abietane with an ether linkage from Taxus cuspidata Needles. Z Naturforsch B 2011; 66: 1083-1086
• 95 Pinto AC, Pizzolatti MG, Epifanio RDA, Frankmolle W, Fenical W. The isolation of novel diterpenoids, including a C-40 bis-diterpenoid, from the Brazilian plant Vellozia magdalenae (Velloziaceae). Tetrahedron 1997; 53: 2005-2012
• 96 Sivasothy Y, Ibrahim H, Paliany AS, Alias SA, Md Nor NR, Awang K. A new bis-labdanic diterpene from the rhizomes of Alpinia pahangensis . Planta Med 2013; 79: 1775-1780
• 97 Ou YX, Li YY, Qian XM, Shen YM. Guanacastane-type diterpenoids from Coprinus radians . Phytochemistry 2012; 78: 190-196
• 98 Yoshida T, Toyota M, Asakawa Y. Scapaundulins A and B, two novel dimeric labdane diterpenoids, and related compounds from the Japanese liverwort Scapania undulata (L) Dum. Tetrahedron Lett 1997; 38: 1975-1978
• 99 Rodriguez AD, Shi JG. Isolation, structure elucidation, and synthesis of bisgersolanolide, a novel heptacyclic bis-diterpenoid from the gorgonian octocoral Pseudopterogorgia bipinnata . Org Lett 1999; 1: 337-340
• 100 Johnstone RW, Frew AJ, Smyth MJ. The TRAIL apoptotic pathway in cancer onset, progression and therapy. Nat Rev Cancer 2008; 8: 782-798
• 101 Obenhuber AH, Gianetti TL, Bergman RG, Arnold J. Regioselective [2 + 2] and [4 + 2] cycloaddition reactivity in an asymmetric niobium(bisimido) moiety towards unsaturated organic molecules. Chem Commun 2015; 51: 1278-1281
• 102 Gao WY, Zhang R, Jia W, Zhang J, Takaishi Y, Duan HQ. Immunosuppressive diterpenes from Veronicastrum sibiricum . Chem Pharm Bull (Tokyo) 2004; 52: 136-137
• 103 Uchida M, Miyase T, Yoshizaki F, Bieri JH, Ruedi P, Eugster CH. Isolation of 14-hydroxytaxodione from Plectranthus grandidentatus Gurke and of 7 new dimeric diterpenoids from Plectranthus grandidentatus, Plectranthus myrianthus and Coleus carnosus – structures of grandidone a, 7-epi-A, B, 7-epi-B, C, D and 7-epi-D. Helv Chim Acta 1981; 64: 2227-2250
• 104 Chen SK, Chen BY, Li H. Flora Reipublicae Popularis Sinicae (Zhongguo Zhiwu Zhi). Beijing: Science Press; 1997
• 105 Hu XM, Zhang WK, Song LR, Hu L, Zhang GZ, Xie ZW, Wang XT, Xu GJ, Xiao PG, Ling YK, Ding XL, Cao CL, Li YK, Yu WX, Hong X, Wang JH. Chinese Materia Medica (Zhonghua Bencao). Shanghai: Shanghai Science and Technology Press; 1999
• 106 Aoyagi Y, Takahashi Y, Satake Y, Fukaya H, Takeya K, Aiyama R, Matsuzaki T, Hashimoto S, Shiina T, Kurihara T. Biomimetic synthesis of grandione from demethylsalvicanol via hetero-Diels-Alder type dimerization and structure revision of grandione. Tetrahedron Lett 2005; 46: 7885-7887
• 107 Majetich G, Zou G. Total synthesis of (−)-barbatusol, (+)-demethylsalvicanol, (−)-brussonol, and (+)-grandione. Org Lett 2008; 10: 81-83
• 108 Kelecom A. Isolation, structure determination, and absolute configuration of barbatusol, a new bioactive diterpene with a rearranged abietane skeleton from the Labiate Coleus barbatus . Tetrahedron 1983; 39: 3603-3608
• 109 Deng J, Zhou SP, Zhang WH, Li J, Li RF, Li A. Total synthesis of taiwaniadducts B, C, and D. J Am Chem Soc 2014; 136: 8185-8188