Synthesis and Characterization of Cyclotriphosphazenes Bearing Six Bile Acid Arms Giancarlo Fantina , Marco Fogagnoloa, and Pier Paolo Giovanninib a b Dipartimento di Chimica, Università di Ferrara, Via Borsari 46, 44100 Ferrara, Italy Dipartimento di Biologia ed Evoluzione, Università di Ferrara, C.so Ercole I d’Este, 32, 44100 Ferrara, Italy Reprint requests to Prof. Marco Fogagnolo. Fax: +39(0)53-2240709. E-mail: fgr@unife.it Z. Naturforsch. 2009, 64b, 551 – 554; received March 16, 2009 Four novel cyclotriphosphazene bile acid derivatives (1 – 4) were prepared starting from hexakis[4(chloromethyl)phenoxy]cyclotriphosphazene (8) as the scaffold. The structures of the compounds were defined by elemental analysis, IR and 1 H, 13 C and 31 P NMR spectroscopy. Key words: Cyclotriphosphazene, Bile Acid, Synthesis, Podant Introduction Bile acids are a most valuable group of compounds due to their large, rigid and curved steroidal skeletons, chemically different hydroxyl groups, enantiomeric purity, unique amphiphilicity, availability, and low cost [1]. For these reasons bile acids are versatile building blocks for the design and synthesis of macrocyclic and open chain supramolecular hosts [2]. There are many kinds of acyclic structures based on bile acids, among which the most interesting are: cleft-type structures [3], molecular tweezers [4], ionophores [5], molecular umbrellas [6], dendrons [7], gelling agents [8], and inclusion compounds (clathrates) [9]. On the other hand, the core ring of cyclotriphosphazenes has proven to be a versatile and valuable building block for new applications in molecular recognition, and a component of functional materials [10]. Despite the versatility of phosphazene chemisty, there is no report, to our knowledge, on the preparation of hexakis-bile acid-substituted cyclotriphosphazene derivatives. In this paper we report the synthesis of four new cyclotriphosphazene derivatives 1 – 4 containing six bile acid arms using the phenoxymethylene fragment as linker (Fig. 1). Results and Discussion Our idea was to build a cyclotriphosphazene bearing six bile acid units, having in principle supramolecular properties. However, the attempts to link directly six steroidal subunits via carboxyl or hydroxyl groups to the cyclotriphosphazene core using the hexachloro derivative 5 failed, probably for steric hindrance, as previously reported [11]. In the hope to overcome the steric crowding, we used chloromethylphenoxy groups as connecting units between the phosphazene ring and the bile acid moieties. Preparation of phosphazenes containing bile acids was achieved from the scaffold of hexakis[4-(chloromethyl)phenoxy]cyclotriphosphazene 8 according to Scheme 1. The structures of the compounds obtained were confirmed by 1 H, 13 C, 31 P NMR and IR spectroscopy and elemental analysis. Our synthesis involved quantitative conversion of the hexaaldehyde 6, readily prepared from hexachlorocyclotriphosphazene 5, and of 4-hydroxybenzaldehyde [10a] into the hexakis-[4-(hydroxymethyl)phenoxy]cyclotriphosphazene 7 via complete reduction of the six formyl groups with an excess of NaBH4 in methanol at 0 ◦C. The hexaalcohol 7 was subsequently treated with thionyl chloride for two days to produce the hexachloromethyl derivative 8 in quantitative yield. The last step consisted of the grafting of 6 equiv. of the appropriate bile acid cesium salt onto hexakis-[4(chloromethyl)phenoxy]cyclotriphosphazene. The reaction was carried out with an excess of bile acid salt (10 equiv.) in DMF at 40 ◦C and needed 3 days to complete, as shown by 31 P NMR monitoring. After simple workup (see Experimental Section) the hexa(bile acid) cyclotriphosphazene derivatives 1 – 4 were obtained in almost quantitative yield without tedious purification. c 2009 Verlag der Zeitschrift für Naturforschung, Tübingen · http://znaturforsch.com 0932–0776 / 09 / 0500–0551 $ 06.00
552 Compound 1 2 3 4 G. Fantin et al. · Cyclotriphosphazenes Bearing Six Bile Acid Arms X Y Z α -OH, H H, H α -OH, H α -OH, H α -OH, H α -OH, H O H, H O O O O Fig. 1. The newly synthetized cyclotriphosphazene-bile acid derivatives 1 – 4. Scheme 1. Synthetic pathway for the preparation of compounds 1 – 4. Reagents and conditions: a: 4-HOC6 H4 CHO, NEt3 , THF; see ref. [10a]; b: NaBH4 , MeOH, 0 ◦C; c: SOCl2 ; d: DMF, 40 ◦C. Conclusion Four new bis-tripodant claw-shaped molecules 1 – 4 based on bile acid and cyclotriphosphazene were easily obtained in good yields in typical procedures shown in Scheme 1. All these compounds are potential supramolecular systems capable to complex guest molecules or ions. This kind of physicochemical studies is under way. Experimental Section General methods. Melting points are uncorrected and were determined on a 510 Büchi melting point instrument. TLC was performed on precoated silica gel plates (thickness 0.25 mm, Merck), and silica gel (Fluka, Kieselgel 60, 70 – 230 mesh) was used for preparative column chromatography. The 1 H, 13 C and 31 P NMR spectra were recorded in CDCl3 and/or CD3 OD solution in 5 mm tubes at r. t., with a Varian Gemini 300 spectrometer with TMS as internal standard for 1 H and 13 C spectra and with phosphoric acid as external standard for 31 P spectra. IR spectra were recorded on a Perkin-Elmer 1310 infrared spectrometer using the Nujol suspension technique. Elemental analyses were performed on a 1106 Microanalyzer (Carlo Erba). Hexachlorocyclotriphosphazene 5 was purchased from Aldrich and purified by vacuum sublimation until a constant melting point (113 ◦C) was obtained. G. Fantin et al. · Cyclotriphosphazenes Bearing Six Bile Acid Arms Hexakis(4-formylphenoxy)cyclotriphosphazene (6) Compound 6 was prepared according to a described procedure [10a]. To a solution of hexachlorocyclotriphosphazene 5 (0.521 g, 1.5 mmol) in 10 mL of THF was added a solution of triethylamine (2.5 mL, 18 mmol) and 4-hydroxybenzaldehyde (2.20 g, 18 mmol) in 30 mL of anhydrous THF. The resulting mixture was refluxed for 16 h and then filtered, and the solvent evaporated. The resulting oil was washed with methanol (2 × 50 mL) to give 6 as a white powder; m. p. 140 – 142 ◦C; (141 – 142 ◦C [10a]); 90 % yield. – IR: ν = 1704 (C=O), 1200 – 1150, 950 cm−1 . – 31 P{1 H} NMR (121.5 MHz, CDCl ): δ = 7.08 (s). – 3 1 H NMR (300.1 MHz, CDCl ): δ = 7.12 (d, J = 8 Hz, 3 12H, Ar-H), 7.72 (d, J = 8 Hz, 12H, Ar-H), 9.91 (s, 6H, CHO). – 13 C{1 H} NMR (78.5 MHz, CDCl3 ): δ = 120.8, 130.7, 133.4, 154.0 (Carom ) 189.6 (C=O). – C42 H30 N3 O12 P3 (861.62): calcd. C 58.54, H 3.51, N 4.87; found C 58.90, H 3.78, N 4.80. Hexakis[4-(hydroxymethyl)phenoxy]cyclotriphosphazene (7) To a stirred suspension of hexakis(4-formylphenoxy)cyclotriphosphazene (6) (1 g, 1.16 mmol) in methanol (50 mL) NaBH4 (0.14 g, 3.7 mmol) was added portionwise at 0 ◦C. After 30 min acetone (1 mL) was added, and the reaction mixture was treated with 5 % aqueous HCl up to pH = 5 and then diluted with water (25 mL). The precipitated alcohol 7 was filtered off and used without further purification. Yield 100 %. – M. p. 210 – 212 ◦C. – IR: ν = 3345 (OH), 1200 – 1150, 950 cm−1 . – 31 P{1 H} NMR (121.5 MHz, CD3 OD): δ = 10.03 (s). – 1 H NMR (300.1 MHz, CD3 OD): δ = 4.59 (s, 12H, CH2 O), 6.88 (d, J = 9 Hz, 12H, Ar-H), 7.20 (d, J = 9 Hz, 12H, Ar-H). – 13 C{1 H} NMR (78.5 MHz, CD3 OD/CDCl3 ): δ = 64.3 (CH2 O), 121.5, 128.8, 139.2, 150.5 (Carom ). – C42 H42 N3 O12 P3 (873.72): calcd. C 57.74, H 4.85, N 4.81; found C 57.90, H 4.78, N 4.90. Hexakis[4-(chloromethyl)phenoxy]cyclotriphosphazene (8) 1 g (1 mmol) of the hydroxymethylene derivative 7 was dissolved, at 0 ◦C, in SOCl2 (2 mL, 0.027 mol). The reaction mixture was left at r. t. for 24 h and, after removing excess thionyl chloride, the residue was treated with H2 O (20 mL). The precipitate was filtered and washed up to pH = 7 with distilled water. Yield almost quantitative. – M. p. 140 – 142 ◦C. – IR: ν = 1200 – 1150, 950 cm−1 . – 31 P{1 H} NMR (121.5 MHz, CDCl3 ): δ = 9.73 (s). – 1 H NMR (300.1 MHz, CDCl3 ): δ = 4.58 (s, 12H, CH2 Cl), 6.93 (d, J = 9 Hz, 12H, Ar-H), 7.24 (d, J = 9 Hz, 12H, Ar-H). – 13 C{1 H} NMR (78.5 MHz, CDCl3 ): δ = 45.5 (CH2 Cl), 121.1, 129.9, 134.2, 150.5 (Carom ). – C42 H36 Cl6 N3 O6 P3 (984.39): calcd. C 51.24, H 3.68, N 4.27; found C 51.00, H 3.78, N 4.40. 553 General procedure for the preparation of bile acid cesium salts The bile acid cesium salts were obtained following [12]. Solid Cs2 CO3 (1.23 mmol) was added to a solution of the appropriate bile acid (2.45 mmol) in MeOH/H2 O (24 mL, 5 : 1 v/v). The reaction mixture was stirred at r. t. for 15 min, then concentrated under vacuum and azeotropically dried with toluene. The obtained cesium salt was used without further purification. General procedure for the synthesis of the hexapodant N3 P3 (O-C6 H4 CH2 -bile acid)6 (1 – 4) 0.108 g (0.11 mmol) of hexakis[4-(chloromethyl)phenoxy]cyclotriphosphazene (8) and 1.1 mmol of the appropriate bile acid cesium salt are added to 3 mL of dimethylformamide. The suspension, kept at 40 ◦C, was shaken for 72 h. An aqueous solution of NaHCO3 (15 mL) was added and the resulting solid collected by filtration and washed with distilled water. Hexakis[4-(3α ,12α -dihydroxy-5β -colanoyloxymethyl)phenoxy]cyclotriphosphazene (1) Yield 95 %; obtained as white crystals. M. p. 240 – 242 ◦C. – IR: ν = 3400 (O-H), 1735 (C=O), 1595, 1200 – 1150, 950 cm−1 . – 31 P{1 H} NMR (121.5 MHz, CDCl3 ): δ = 9.78 (s). – 1 H NMR (300.1 MHz, CDCl3 ): significant sorting δ = 0.68 (s, 18H, 18-CH3 ), 0.92 (s, 18H, 19-CH3 ), 0.98 (d, J = 6.8 Hz, 18H, 21-CH3 ), 3.62 (m, 6H, 3β -CH), 3.98 (br s, 6H, 12β -CH), 5.05 (A part of AB system, J = 12.6 Hz, 6H, Ar-CH-O), 5.10 (B part of AB system d, J = 12.6 Hz, 6H, Ar-CH-O), 6.90 (d, J = 9 Hz, 12H, Ar-H), 7.20 (d, J = 9 Hz, 12H, Ar-H). – 13 C{1 H} NMR (78.5 MHz, CD3 OD/CDCl3 ): significant sorting δ = 65.2 (Ar-CH2 -O), 71.2 (3-CH), 72.7 (12-CH), 120.8 (ArCH), 129.3 (ArCH), 132.8 (ArC), 150.8 (ArC), 174.2 (COO). – C186 H270 N3 O30 P3 (3121.06): calcd. C 71.58, H 8.72, N 1.35; found C 71.90, H 8.78, N 1.50. Hexakis[4-(3α ,7α ,12α -trihydroxy-5β -colanoyloxymethyl)phenoxy]cyclotriphosphazene (2) Yield 96 %; obtained as white crystals. M. p. 252 – 255 ◦C. – IR: ν = 3400 (O-H), 1720 (C=O), 1495, 1150, 945 cm−1 . – 31 P{1 H} NMR (121.5 MHz, CD3 OD): δ = 10.12 (s). – 1 H NMR (300.1 MHz, CD3 OD/CDCl3 ): significant sorting δ = 0.68 (s, 18H, 18-CH3 ), 0.90 (s, 18H, 19-CH3 ), 1.00 (d, J = 6.8Hz, 18H, 21-CH3 ), 3.38 (m, 6H, 3β -CH), 3.80 (br s, 6H, 7β -CH ), 3.94 (br s, 6H, 12β -CH), 5.13 (br s, 12H, Ar-CH2 -O), 6.86 (d, J = 9 Hz, 12H, Ar-H), 7.24 (d, J = 9 Hz, 12H, Ar-H). – 13 C{1 H} NMR (78.5 MHz, CD OD/CDCl ): significant 3 3 554 G. Fantin et al. · Cyclotriphosphazenes Bearing Six Bile Acid Arms sorting δ = 66.2 (Ar-CH2 -O), 68.9 (7-CH), 72.6 (3-CH), 73.8 (12-CH), 121.9 (ArCH), 130.5 (ArCH), 134.5 (ArC), 151.2 (ArC), 175.3 (COO). – C186 H270 N3 O36 P3 (3217.05): calcd. C 69.44, H 8.46, N 1.31; found C 69.51, H 8.70, N 1.42. Hexakis[4-(3,12-dioxo-5β -colanoyloxymethyl)phenoxy] cyclotriphosphazene (3) Yield 95 %; obtained as white crystals. M. p. 170 – 175 ◦C. – IR: ν = 1695 (C=O), 1150, 945 cm−1 . – 31 P{1 H} NMR (121.5 MHz, CDCl3 ): δ = 9.49 (s). – 1 H NMR (CDCl3 ): significant sorting δ = 0.86 (d, J = 6.8Hz, 18H, 21CH3 ), 1.05 (s, 18H, 18-CH3 ), 1.13 (s, 18H, 19-CH3 ), 5.08 (br s, 12H, Ar-CH2 -O), 6.92 (d, J = 9 Hz, 12H, Ar-H), 7.20 (d, J = 9 Hz, 12H, Ar-H). – 13 C{1 H} NMR (78.5 MHz, CDCl3 ): significant sorting δ = 65.3 (Ar-CH2 -O), 120.9 (ArCH), 129.4 (ArCH), 133.0 (ArC), 150.3 (ArC), 173.8 (COO), 212.2 (3C=O), 214.1 (12C=O). – C186 H246 N3 O30 P3 (3096.87): calcd. C 72.14, H 8.01, N 1.35; found C 71.27, H 8.08, N 1.30. [1] a) D. Kritchevsky, P. P. Nair in The Bile Acids: chemistry, physiology and metabolism, Vol. 1 (Eds.: P. P. Nair, D. Kritchevsky), Plenum, New York, 1971, pp. 3 – 9; b) E. Virtanen, E. Kolehmainen, Eur. J. Org. Chem. 2004, 3385 – 3399; c) S. Mukhopadhyay, U. Maitra, Curr. Science 2004, 87, 1666 – 1683; d) O. Bortolini, G. Fantin, M. Fogagnolo, Chirality 2005, 17, 121 – 130; e) Nonappa, U. Maitra, Org. Biomol. Chem. 2008, 6, 657 – 669. [2] a) A. P. Davis, Chem. Soc. Rev. 1993, 243 – 253; b) Y. Li, J. R. Dias, Chem. Rev. 1997, 97, 283 – 304; c) P. Wallimann, T. Marti, A. Fürer, F. Diederich, Chem. Rev. 1997, 97, 1567 – 1608; d) E. Kolehmainen, J. Tamminen, Molecules 2001, 6, 21 – 46; e) A. P. Davis, Molecules 2007, 12, 2106 – 2122. [3] a) J. McKenna, J. M. McKenna, D. W. Thornthwaite, J. Chem. Soc., Chem. Commun. 1977, 809; b) J. T. Tamminen, E. T. Kolehmainen, M. H. Haapala, H. T. Salo, J. M. Linnanto, Arkivoc 2000, i, 80 – 86; c) Z. Lotowski, D. Guzmanski, Monats. Chem. 2006, 137, 117 – 124. [4] a) L. J. D’Souza, U. Maitra, J. Org. Chem. 1996, 61, 9494 – 9502; b) V. K. Potluri, U. Maitra, J. Org. Chem. 2000, 65, 7764 – 7769. Hexakis[4-(3,7,12-trioxo-5β -colanoyloxymethyl)phenoxy] cyclotriphosphazene (4) Yield 95 %; obtained as white crystals. M. p. 180 – 185 ◦C (dec.). – IR: ν = 1695 (C=O), 1145, 945 cm−1 . – 31 P{1 H} NMR (121.5 MHz, CDCl3 ): δ = 9.52 (s). – 1 H NMR (300.1 MHz, CDCl3 ): significant sorting δ = 0.84 (d, J = 6.8Hz, 18H, 21-CH3 ), 1.06 (s, 18H, 18-CH3 ), 1.20 (s, 18H, 19-CH3 ), 5.05 (A part of AB system, J = 12 Hz, 6H, Ar-CHO), 5.12 (B part of AB system d, J = 12 Hz, 6H, Ar-CH-O), 6.92 (d, J = 9 Hz, 12H, Ar-H), 7.21 (d, J = 9 Hz, 12H, ArH). – 13 C{1 H} NMR (78.5 MHz, CDCl3 ): significant sorting δ = 65.3 (Ar-CH2 -O), 121.0 (ArCH), 129.5 (ArCH), 133.0 (ArC), 150.2 (ArC), 173.7 (COO), 208.7 (7C=O), 209.2 (3C=O), 211.9 (12C=O). – C186 H234 N3 O36 P3 (3180.77): calcd. C 70.23, H 7.42, N 1.32; found C 70.67, H 7.88, N 1.30. Acknowledgements We are grateful to FAR (2008) of the University of Ferrara for grants supporting this work. In addition, we thank Mr. Paolo Formaglio for NMR measurements. [5] P. Bandyopadhyay, V. Janout, L. Zhang, J. A. Sawko, S. L. Regen, J. Am. Chem. Soc. 2000, 122, 12888 – 12889. [6] V. 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