Solomon Derese, PhD. University of Nairobi. The 7 th International Conference of the Kenya Chemical Society October 15-18, 2012, Maseno

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1 Solomon Derese, PhD University of Nairobi The 7 th International Conference of the Kenya Chemical Society October 15-18, 2012, Maseno 1

2 Why should we look for drugs from natural products in Africa? Africa has rich and diverse biodiversity. Biodiversity is an outward representation of chemical diversity. Africa has rich and alive heritage in traditional medicine. 2

3 Erythrina abyssinica, a very important antimalarial plant, in the middle of the farm 3

4 Steps in Drug Discovery from Traditional Medicine Ethnobotany Phytochemistry Bioassay 4

5 Flavonoids as a toll to control malaria O From Polykeide pathway O From shikimic acid pathway 5

6 Control of malaria Antiplasmodial Larvicides 6

7 Larvicides activity of flavonoids against 2 nd instar Aedes aegypi 7

8 Rotenoids with cis B/C ring junction Derris (Asia) Lonchocarpus (South America) Tephrosia Millettia Rotenone LC 50 = 1.32 mm R 1 Deguelin H 4.06 Tephrosin OH 3.65 LC 50 (mm) 8

9 R 1 LC 50 (mm) Millettone H > 50 mm Millettossin OH > 50 mm Dehydrodeguelin Inactive, LC 50 > 50 mm Dehydrorotenone Inactive, LC 50 > 50 mm 9

10 Rotenoids with trans B/C ring junction Inactive, LC 50 > 50 mm Inactive, LC 50 > 50 mm Inactive, LC 50 > 50 mm 10 Inactive, LC 50 > 50 mm

11 Structural requirement for rotenoids to have larvicidal activities cis B/C ring junction methoxyl groups at C-2 and/or C-3 saturation at the B/C ring junction 11

12 Derris trifoliata Mangrove tree Phytochemistry 2005, ; 2006,

13 Are these compounds larvicidal? 13

14 Biogenesis of spiro-13-homo-13-oxaelliptone 14

15 LC 50 = mm LC 50 =1.32 mm R 1 LC 50 (mm) H 4.06 OH

16 Other classes of flavonoids were inactive 16

17 In vitro antiplasmodial activities of flavonoids against D6 (CQS) and W2 (CQR) of P. falciparum 17

18 Millettia usaramensis Phytochemistry 1998, ; 2003,

19 O O H O O O O H O O OH O O O OH O O W2 D6 IC 50 in mg/ml (mm) 6.9 (17.5) 14.5 (36.8) W2 D6 IC 50 in mg/ml (mm) 6.6 (18.6) 11.9 (33.4) O O O H O MeO O H O W2 D6 OH OH O O IC 50 in mg/ml (mm) 2.6 (7.4) >50 W2 D6 O OH IC 50 in mg/ml (mm) O 14.8 (36.0) 8.5 (20.7) O 19

20 IC 50 in mg/ml (mm) W (31.0) D6 7.4 (18.8) IC 50 in mg/ml (mm) D6 6.8 (17.2) 20

21 Tephrosia elata SEEDPODS Phytochemistry letters 2009,

22 REVISION OF LITRATURE STRUCTURES Characteristic 13 C NMR peaks of b- hydroxydihydrochalcone and flavanones Position b-hydroxydihydrochalcone Flavanones a (3) ~52 ppm ~42 ppm b (2) ~70 ppm ~ 80 ppm 22

23 All known b- hydroxydihydrochalcones in nature 23

24 Antiplasmodial test results Elatadihydrochalcone b-acetoxyelatadihydrochalcone IC 50 (mm) D6 7.9 ± 0.3 W ± 0.3 IC 50 (mm) D ± 2.1 W ±

25 IC 50 (mm) R D6 W2 Obovatin H 15.2 ± ± 1.1 Obovatin methyl ether Me 11.3 ± ±

26 Erythrina abyssinica Root and stem bark decoction is used to treat malaria and syphilis Phytochemistry 1998, p. 247; 1998, p. 1439; 2002, p. 337; , p. 658 and 2004, p

27 Chalcones IC 50 = mm (D6) = mm (W2) IC 50 = mm (D6) = mm (W2) IC 50 = mm (D6) = mm (W2) 27

28 Flavanones with one prenyl groups IC 50 = 13.6 mm (D6) = 13.3 mm (W2) IC 50 = 17.8 mm (D6) = 15.8 mm (W2) IC 50 = 8.1 mm (D6) = 9.3 mm (W2) IC 50 = 13.0 mm (D6) = 12.7 mm (W2) 28

29 Flavanones with two prenyl groups IC 50 = 5.8 mm (D6) = 5.2 mm (W2) IC 50 = 5.8 mm (D6) = 5.9 mm (W2) IC 50 = 4.9 mm (D6) = 6.1 mm (W2) IC 50 = 11.3 mm (D6) = 11.1 mm (W2) 29

30 Flavanones with two prenyl groups (contd) 30

31 Pterocarpans 31

32 Isoflav-3-enes IC 50 = 8.2 mm (D6) = 27.6 mm (W2) 32

Comparison of the anti-plasmodial activities of the flavonoids of Erythrina abyssinica IC 50 in mm 25 20 15 10 5 D6 W2 0 Chalcones

33 Comparison of the anti-plasmodial activities of the flavonoids of Erythrina abyssinica IC 50 in mm D6 W2 0 Chalcones Monoprenylated flavanones Diprenylated flavanones Pterocarpans Isoflav-3-ene IC 50 = mm Lichochalcone A (from Chinese liquorice root) 33

34 Where from here. 34

35 Optimizing the larvicidal/antiplasmodial activity of the flavonoids to control malaria I. Synthesis of analogues Electron Donating Electron Withdrawing Lipophilic Hydrophilic 35

36 II. Computer-Aided Drug Design Develop an in silico database of natural products isolated from Kenyan plants to be used in: Structure and/or Ligand based drug design. 36

37 There are hundreds of natural products with diverse skeletons isolated from Kenyan plants which have been used through the ages traditionally to treat various ailments. Compounds from these library or their derivatives could yield the next generation of drugs. Mitishamba in silico database of NPs 37

2D Structure of Natural Products (NP) Rough 3D structures of NP Coarse-grained method Similarity search against Cambridge Structured database (CSD ) Is there a compound with a solved crystal in the

38 2D Structure of Natural Products (NP) Rough 3D structures of NP Coarse-grained method Similarity search against Cambridge Structured database (CSD ) Is there a compound with a solved crystal in the CCD database structure similar to NP? Yes Flexible ligand alignment of NP to a similar crystal structure No Molecular Mechanics Geometries of many distinct Conformations of NP Quantum Mechanics Energies of many distinct 3D Conformations of NP Take only lowest energy structure ab initio method Refined guess of the three dimensional structure of NP mitishamba database 38

39 Acknowledgements 39

40 Co-Supervisors/Mentors Prof. J. O. Midiwo Prof. Abiy Yenesew 40

41 High Resolution NMR, MS etc Prof. Dr. M. G. Peter Dr. M. Heidenreich University of Potsdam, Germany 41

42 Antiplasmodial assay United States Army Medical Research Unit-Kenya (USAMRU-K) Hosea M Akala, Julia Wangui, Fredrick Eyase Pamela Liyala, Christine Wasuna and Norman C. Waters 42

48 Graduates

49 Graduation party

50 Graduates

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution