An Approach to New Water-soluble Oligo(ethylene glycol) Camptothecin Analogues by 1,3-Dipolar Cycloa

Chinese Chemical Letters Vol. 17, No.7, pp 883-886, 2006883http://www.imm.ac.cn/jouma/ccl.htmlAn Approach to New Water-soluble Oligo(ethylene glycol)Camptothecin Analogues by 1,3-Dipolar CycloadditionChun Yan XU*, Ming Zhi HUANGCollege of Materials Science and Technology, Beijing Uniersity of Chemical Technology,Beijing 100029Abstract: Combined with an effective copper-catalyzed triazole-forming reaction, a series of novelcamptothecin derivatives were synthesized. Incorporaing oligo(ethylene glycol) chains into thederivatives enhanced their water-solubility when compared to the parent compound (up to 55-fold).Keywords: Click chemistry, 20(S)-camptothecin, water-soluble derivatives.20(S)-Camptothecin (CPT) 1 (Figure 1) is an antitumor alkaloid which was first isolatedfrom the Chinese tree Camptotheca acuminata by Wall and coworkers in 1966' andlately also from the Indian tree Nothapodytes foetida by Govindachari and Viswanathan*.This alkaloid has showed significant inhibitory activity toward a variety of tumor typesboth in pre clinical and early phase I clinical studies'. However, poor solubility of CPT1 precluded its development as a clinical agent and the water-soluble sodiumcamptothecin 2 (Figure 1) demonstrated antitumor activity in animal models comparableto that of CPT 1, it was about 10-fold less potent with respect to therapeutic dosagerange* and severe toxicity of the salt to the bone marrow and bladder led to suspension ofthe clinical trials.In the late 1980s, the discovery that the primary cellular target for CPT 1 is DNAtopoisomerase r has created renewed interest in the compound. Therefore, manycamptothecin analogues through a number of approaches have been prepared to improvethe antitumor efficiency of the CPT family48. For example, topotecan 3' and irinotecan40 (Figure 1) have been successfully used in some countries for the treatment of ovarianand small-cell lung cancers and for colorectal cancer, respectively.At least 10additional CPT analogues are in various phases of clinical trials and the synthesis andidentification of new water soluble CPT analogues are still to be of great interest.1,3-Dipolar cycloaddition reactions are powerful methods for the preparation of avariety of cyclic compounds. It is well-known that the 1,3-dipolar cycloaddition of anazide with an alkyne leads to the formation of 1,2,3-tri中国煤化工/orkersdeveloped a copper (1)-catalyzed version, termnedCNMHGoceedsreadily at physiological temperatures and in richly functuonalizea blological environs.'E- mail: xucy0643@ 126.com884Chun Yan XU et al.Figure 1 Chemical structures of 20(S)-camptothecin 1, sodium camptothecin 2,topotecan 3 and irinotecan 4//1/HNaHO 0HO012N.HO、0、9/"Ho o1, 2, 3-Triazoles may display a wide range of biological activity, such as anti-HIV'5 andantimicrobial agents'4, as well as selective β3 adrenergic receptor agonists'We are conducting a study on chemical modification of CPT 1 as a starting materialto obtain more water-soluble and less toxic derivatives. In this report we described thesynthesis of derivatives of 10-hydroxycamptothecin bearing 1, 2, 3-triazoles with intactlactone ring which is believed to be essential for the antitumor activity.The synthetic route is outlined in Scheme 1. 5 and 6 were prepared according tothe literaturel6. The hydroxyl group of 6 was converted into a propargyl ether usingK2CO3 and propargyl bromide to afford the required alkyne 7 for click reaction. Weassumed that employing linkers with an oligo(ethylene glyco) backbone would enhancethe water solubility of the camptothecins. With azides 8a-d in hand'", we next tried toincorporated them with 7 to form oligo(ethylene glycol) camptothecins 9a-d for furtherbioassay studies. Our first attempt of click chemistry was carried out by treatment of 7with 8a using Cul/TEA as catalyst in CHzCN at r.t. for 48 h (entry 1, Table 1). Nreaction took place. However, when the reaction was stirred for 12 h under theconditions of CuSO,/Sodium ascorbate in t-BuOHx8, 9a was obtained in 30% yield (entry2, Table 1). To optimize the reaction conditions, the effect ratio of alkyne/azide/catalyst and solvents were studied. As showed in Table 1, the reaction gives asatisfactory yield in the ratio of 1:1.25:0.1 in 1:1 H2O: DMF. Under very similarconditions, the other azides 8b d underwent click chermistry to yield corresponding 1,2,3-triazoles 9b-d in 70%-77%. All compounds were characterized and identified by IR, H,'3C and ESI-MS as well as elemental analysis,中国煤化工ement withthe proposed structures. The representativeollows: 'HMHCNMHG2H,J=42NMR (400MHz, CDCl3, δ ppm): 0.95 (t, 3H, J= 7.J.1),1.0 (4ll, ,Hz), 3.66(t, 2H, J= 4.2 Hz), 3.85(, 2H, J= 4.8 Hz), 4.54(1, 2H, J= 4.8 Hz), 5.13(, 2H),5.18(s, 2H), 5.24(s, 2H), 7.20(s, 1H), 7.34(d, 1H, J= 2.4 Hz), 7.52(dd, 1H, J= 9.2, 2.4Hz), .An Approach to New Water-soluble Oligo(ethylene glycol) Camptothecin 885AnaloguesScheme 1 Synthesis of compounds 9a-dHO、0HCHO oHO6= 0./"OH 0n=0,1,23to~OH9a-d8a-d N3n=0,1,2,3(a) H2O2, HAc, 61%; (b) H2SO4 H2O, Hv, 54%; (c) Propargyl bromide, K2CO3, DMAc, 62%; (d)8a-d, CuSO/Sodium ascorbate, H2O/DMF7.86(s, 1H), 7.98(d, 1H, J= 9.2), 8.13(s, 1H); BC NMR (400MHz, CDCI], δ, ppm): 6.81,28.68, 30.60, 49.06, 49.41, 60.63, 61.29, 65.31, 68.21, 71.77, 96.47, 105.83, 117.10,122.67, 123.18, 128.08, 128.33, 128.61, 130.22, 142.28, 144.09, 145.56, 149.20, 149.27,156.41, 156.61, 172.90; ESI-MS found m/z 534.25[M+1]*, 534.53 (calcd).Table 1 Reaction conditions and resultsEntryAlkyne(eq,)Azide(eq.)Catalyst system(eq.)solventYield(%)7(1)8a(2)CuI (0.05)/TEA(1.0)CHzCNNo reaction8a (2)CuSO4 (0.05)/pyidineSodium ascorbate (0.1)CuSOs (0.05)/H20/1-BuOH2:CuSO4 (0.05)11:1 H2O:DMF545CuSO4 (0.1)11:1 H20:DMF84Sodium ascorbate (0.2)8a (1)78a(1.25)CuSO, (0.1)1/838b (1.25)8c (1.25)中国煤化工0Sodium ascorbate (88d (1.25)YHCNMHG7Sodium ascorbate (0.2886Chun Yan XU et al.Water solubility of compounds 9a-d and CPT 1 was determined by measuring theUV absorbance of a saturated solution of the respective compounds in isotonic NaCl-solution. The results are shown in Table 2. We observed that water solubility of 9a-dimproved with increasing numbers of intermnalized ether bonds. Compound 9d whichincorporated the longest oligo(ethylene glycol) spacer, turned out to be 55-fold morewater soluble than CPT 1.In summary, we have prepared a series of camptothecin derivatives containingoligo(ethylene glycol) which enhanced their water-solubility when compared to theparent compound. In vitro pharmacological evaluation is in the progress.Table 2 Water- solubilities of the derivatives 9a-d and camptothecin 1 determined by UVmeasurement (n = 370 nm) of saturated solutions (0.9% NaCl solution)CompoundMW[g/mollSolubilitylumolL]Solubiltyug/mL]1348.352..9a489.489691533.539577.59126621.64384239ReferencesM. E. Wall, M. C. Wani, C. E. Cook, K. H. Palmer, J. Am. Chem. Chem, 1966, 88, 3888.2. T. R. Govindachari, N. Viswanathan, Indian J. Chem, 1972, 10, 453.3. J. O'Leary, F. M. Muggia, Eur. J. Cancer, 1998, 34(10), 1500.4. M. C. Wani, P. E. 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Nokata, et al, Chem. Pharm. Bull, 1991, 39(12), 3183.17. C. R. Berozzi, M. D. Bednarski, J. Org. Chem., 1991, 56, 4326.18. V. V. Rostovtsev, L. G. Green, V. V. Folkin, et al, Angew. Chem, Int. Ed, 2002, 4I, 2596.Received 28 February, 2006中国煤化工MYHCNMHG