Chang, YT

Chung, SK

Sohn, KH

Chemical Communications

포항공과대학교

Practical divergent synthesis of all possible regioisorners of myo-inositol trisphosphates Sung-Kee Chung," Young-Tae Chang and Kwang-Hoon Sohn Department of Chemistry, Pohang University of Science and Technology, Pohang, 790-784, Korea The synthesis of all possible 12 regioisomers of IP3, some of which are implicated as second messengers in cellular signalling, is accomplished from myo-inositol via its tribenzoate derivatives(IBz3) as the key intermediates. D-myo-Inositol- 1,4,5-trisphosphate [I( 1,4,5)P3] receptors are a homologous family of tetrameric ligand-gated Ca2+ channels which allow mobilization of intracellular Ca2+ stores in response to activation of cell-surface receptors linked to I( 1,4,5)P3 generation. Although the ligand recognition site of the IP3 receptors appears to be in the N-terminal region, the exact nature of the molecular interactions is not understood. Several other IP3s are also found in living systems, and studies to elucidate the receptor binding as well as the metabolism are in Systematic research on the relationship between the structure and biological function in these areas would be greatly facilitated by the ready availability of all IP3 regioisomers. Until now nine out of the possible 12 (enantiomerically 20) IP3 isomers have been synthesized by independent chemical routes: I( 1,4,6)P3,9 I( 1 ,5,6)P3,lo I(2,4,5)P31 1 and I(2,4,6)P3.7 Here we report a simple, divergent synthesis of all the possible 12 regioisomers of IP3s via inositol tribenzoates (IBz3). One of the key problems in the synthesis of inositol phosphates is to prepare suitable, selectively protected inositol intermediates. We have previously reported syntheses of all the possible nine regioisomers of IP4 through IBz212 which were obtained by benzoyl group migration among the vicinal hydroxy groups of the myo-inositol structure.13 Based on the same synthetic strategy, the benzoyl migration technique was applied to the facile generation of all 12 regioisomers of myo- inositol tribenzoate(IBz3) 1, the key synthetic intermediates, which were then readily phosphorylated to provide the target IP3 structures 2 (Scheme 1). Thus, the random, divergent benzoyl group migration in compound lg ,  prepared from myo- inositol,7 was successfully effected by treatment with 60%. aq. pyridine at elevated temperatures. HPLC analysis conditions (RP18 Alltech, 250 X 4.6 mm, Mobile phase: MeCN: MeOH : H20 (2 : 4 : 5) ,  Flow rate: 1.5 ml min-1) were found, which allowed separation of 10 out of the total 12 regioisomers (la-1) present in the reaction mixture. The structures of the isolated regioisomers of 1 could be readily elucidated by I(1,2,3)P3,3 I(1,2,6)P3,4 1(1,3,4)P3 ,5 I(1,3,5)P3,6,7 I(1,4,5)P3,* 0 ,BZ3 i, ii - 0,(po3Et2)3Bz3 iii, iv, v, v; 0" 0 O ~ L O  i o,-y..o * 1 2a-I 3 Scheme 1 Reagents and conditions: i, diethyl chlorophosphite (10 equiv.), diisopropylethylamine, DMF, -42 -+ 25 OC, 1 h; ii, hydrogen peroxide (35%), sodium phosphate buffer (1.0 mol dm-3, pH 7), 0°C (70-99% overall yield); iii, Me&Br, CH2C12, 25 "C, 1 d; iv, 1 mol dm-3 LiOH, 80 OC, 3 h; v, Dowex 50 X 8-100(H+). Benzoic acid produced was extracted with CH2C12; vi, pH adjusted to 10 (80-99% overall yield). 1H NMR spectroscopy. The increasing order of the HPLC retention time of these regioisomers was found to be lf, g, k, b, e, h, c,  j, i, (a + 1) and d. a 1(4,5,6)Bz3 b I(3,5,6)Bz3 = I( 1,4,5)Bz3 c 1(3,4,6)B~3 = I( 1 ,4,6)Bz3 d I(3,4,5)B~3 = I(1,5,6)B~3 e I(2,5,6)Bz3 = I(2,4,5)Bz3 f I(2,4,6)B~3 g 1(2,3,6)B~3 = I(1,2,4)Bz3 h I(2,3,5)Bz3 = I( 1,2,5)Bz3 i I(2,3,4)Bz3 = I( 1,2,6)Bz3 j I(1,3,6)Bz3 = I(1,3,4)Bz3 k I( 1,3,5)Bz3 1 I( 1,2,3)Bz3 a 1(1,2,3)P3 b I( 1 ,2,4)P3 = I(2,3,6)P c I( 1 ,2,5)P3 = 1(2,3,5)P d 1(1,2,6)P3 = 1(2,3,4)P e I( 1 ,3,4)P3 = I( 1,3,6)P f I( 1,3,5)P3 g I(1,4,5)P3 = I(3,5,6)P h I( 1,4,6)P3 = I(3,4,6)P i I(1,5,6)P3 = I(3,4,5)P3 j I(2,4,5)P3 = I(2,5,6)P3 k I(2,4,6)P3 1 I(4S96)p3 The separational difficulties associated with the mixture of 12 regioisomers could be substantially eased by carrying out the benzoyl group migrations in partially protected derivatives of IBz3. In the event, compounds 4 and 5, prepared from myo- inositol,14 were hydrolysed in acid and then selectively benzoylated on the axial 2-OH by way of the orthoester intermediates to give the two IBz3, l g  and li.7 Each IBz3 was monoacetalized under kinetic conditions to give the 4,5-acetal6 and the 1,6-aceta17. Compound 8, prepared from 4 by selective hydrolysis,12 was monobenzoylated to give a mixture of the 1,2-acetals 9 and 10 (Scheme 2). When compounds 6 ,7  and the mixture of compounds 9 and 10 were subjected to 60% aq. pyridine conditions and then 80% aq. acetic acid under reflux, three sets of four regioisomers providing a total of 10 different IBz3 were obtained from the limited benzoyl group migrations. The kinetic behaviours of the benzoyl migration in each case was conveniently monitored by HPLC at various temperatures. More importantly, in these cases, the individual regioisomer was easily separated by silica gel chromatography at two stages, i.e. with or without the acetonide group. However, the remaining two IBz3 intermediates If and l k  could not be obtained by this method and had to be separately prepared from myo-inositol orthoformate 11 (Scheme 3). Benzoylation of compound 11, derived from myo-inositol,15 followed by acid- catalysed hydrolysis gave If. Alternatively, benzylation of 11, followed by acid-catalysed hydrolysis, benzoylation and then hydrogenolysis provided lk .  Each of the 12 regioisomers thus obtained was fully characterised by 1H and 13C NMR including H-H COSY and FAB mass spectroscopy. Each pure IBz3 isomer 1 was separately phosphorylated by successive treatment with (i) diethyl chlorophosphite and N,N- diisopropylethylamine in DMF and (ii) 35% hydrogen per- oxide12 to yield all 12 regioisomers of compound 2, which were thoroughly characterized by 'H, 13C and 3lP NMR including H-H COSY and FAB mass spectroscopy.? In the final steps, the protecting groups of 2 were removed by successive treatment with trimethylsilyl bromide and then LiOH. The product 3 was obtained after chromatography on Dowex 50 X 8-100 (H+ form), pH adjustment to 10 (LiOH) and then 1yophilization.S It is now clear that all 39 regioisomers of the myo-inositol phosphates(IP,) can be conveniently synthesized by acyl group migration as demonstrated here and previously12716 Fur- Chem. Commun., 1996 163 Published on 01 January 1996. Downloaded by Pohang University of Science and Technology on 22/04/2015 12:44:53. View Article Online / Journal Homepage / Table of Contents for this issueOH HO" o$r:: OH , 1 iii, IV, v, 48% 4 BzO' 'OH BzO'. "OH OH OH l g  8 1 VI, 65% BzO" 5 1 iii, iv, v, 66% BzO' zofJ;~ OH li 1 vi, 45% "OQ.;y BzO'OH OH, OBz 6 9 5BZ, 46% 7 1 vii, iii 1 vii, iii 1 vii, iii 10 6Bz,24% l g ,  li, lj, 11 la ,  lb,  lc, Id Id, le, I f ,  l g  Scheme 2 Reagents and conditions: i, 2,2-dimethoxypropane, pTSA, DMF, 100°C, 3 h; ii, BzC1, pyridine, room temp. fractional crystallization; iii, 80% aq. AcOH, reflux, 30 min; iv, trimethyl orthobenzoate, pTSA, THF, room temp.; v, drops of water; vi, 2-methoxypropene, pTSA, THF, room temp.; vii, pyridine-water (6 : 4), 100 "C; viii, cat. pTSA, MeOH-CH2CI2 (1 : 3), room temp., 1.5 h; ix, BzCl (1.2 equiv.), pyridine thermore, the acyl group migration in conjuction with efficient separation techniques represents a method of generating molecular diversities in small molecules and in particular might prove to be a very useful and general synthetic strategy to generate a diverse molecular array of carbohydrate isomers which would be necessary for the determination of structural specificities in their reactions with biological macromolecules such as receptors, enzymes and antibodies. This work was supported by the Korea Science & Engineer- ing Foundation (Centre for Biofunctional Molecules) and the Ministry of Education (Basic Science Research Fund). Footnotes t 3lP NMR data (121.5 MHz, CDC13, 25 "C, 85% H3P04 as reference) for IBz3 (P03Et2)3 2. For 2a: aP - 0.53(2 P) -1.76. For 2b: Sp -0.59, -0.73 and - 1.42. For 2c: 6 p  -0.59, -0.78 and -1.54. For 2d: aP -0.53, -1.26 and - 1.59. For 2e: 8p -0.84(2 P) and - 1.40. For 2f aP -0.59 and -0.8 l(2 P). 2g: aP -0.89, -1.06 and -1.51. For 2h: aP -0.75, -0.92 and -1.54. For 2i: B p  -0.98, - 1.11 and - 1.73. For 2j: ap -0.64 and - 1.28(2 P). For 2k: hP -0.59 and -0.73(2 P). For 21: aP -0.98 and -1.45(2 P). $. 3IP NMR data (121.5 MHz, D20, 25 "C, 85% H3P04 as reference, pH 10) for IP3 3. For 3a: aP 5.81(2 P) and 4.27. For 3b: aP 5.67,5.53 and 5.44. For 3c: aP 5.69 and 5.50(2 P). For 3d: aP78, 5.39 and 4.88. For 3e: aP 5.75,5.11 and 4.30. For 3f: lip 5.78 and 5.1 l(2 P). For 3g: aP 5.58,5.39 and 4.94. For 3h: aP 6.08, 5.75 and 4.33. For 3i: bP 5.86, 5.22 and 4.74. For 3j: aP 5.92, 5.64 and 5.36. For 3k: 8 p  5.94(3 P). For 31: aP 6.03(2 P) and 4.77. References 1 B. V. L. Potter, Nut. Prod. Rep., 1990, 1; M. J. Berridge, Nature (London), 1993, 361, 315; D. C .  Billington, The inositol phosphates, 11 1 i i ,  81 % BzO' BzO' Ho$f:: OH I f  OBn B n O  O q - I B n  0 13 1 iii, ii, 95% OBn B n O  zofJ::: OBz 14 I v, 99% OH BzoQ:: HO'- OBz l k  Scheme 3 Reagents and conditions: i, triethyl orthoformate, pTSA, DMF, 100°C, 1 d; ii, BzCl, pyridine, room temp.; iii, pTSA, methanol, room temp., 1 h; iv, BnBr, NaH, DMF; v, H2-Pd(OH)2, EtOAc-MeOH 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Chemical synthesis and Biological significance, VCH, Weinheim, 1993. Inositol Phosphates and Derivatives, ed. A. B. Reitz, ACS Symposium Series 463, ACS, Washington DC, 1991. I. D. Spiers, S. Freeman, D. R. Poyner and C. H. Schwalbe, Tetrahedron Lett., 1995, 36, 2125. T. Desai, A. Fernandez-Mayoralas, J. Gigg, R. Gigg, C. Jaramillo, S. Payne, S. Penades and N. Schnetz, ref. 2, p. 86. S. Ozaki, M. Kohno and H. Nakahira, Chem. Lett., 1988, 77; C. E. Ballou and W. Tegge, ref. 2, p. 33; D. M. Gou and C. S. 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Res., 1991, 217, 107; Y. Watanabe, T. Ogawara, N. Shiotani and S. Ozaki, Tetrahedron Lett., 1987, 28, 2607. S.-K. Chung and Y.-T. Chang, J. Chem. SOC., Chem. Commun., 1995, 11. S.-K. Chung and Y.-T. Chang, J. Chem. Soc., Chem. Commun., 1995, 13. S.-K. Chung and Y. Ryu, Carbohydr. Res., 1994,258, 145. H. W. Lee and Y. Kishi, J. Org. Chem., 1985,50,4402. P. J. Cullen, S.-K. Chung, Y.-T. Chang, A. P. Dawson and R. F. Irvine, FEBS Lett., 1995, 358, 240. Received, 11th August 1995; Corn. 5105405B 164 Chem. Commun., 1996 Published on 01 January 1996. Downloaded by Pohang University of Science and Technology on 22/04/2015 12:44:53. View Article Online

Practical divergent synthesis of all possible regioisomers of myo-inositol trisphosphates

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Practical divergent synthesis of all possible regioisomers of myo-inositol trisphosphates

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