Synthesis of Dianhydrohexitole-based Benzamidines as Factor Xa Inhibitors Using Cross Couplings, Phenyl Ether and Amidine Formations as Key Steps

Abstract

Starting with isosorbide or isomannide several dianhydrohexitole-based benzamidines were synthesized as potential factor Xa inhibitors. The key steps for the synthesis of the bisbenzamidines were nucleophilic aromatic substitutions and Mitsunobu reactions to build up phenylethers. Another type of monobenzamidines had ortho-substituted biphenyl groups. Their synthesis necessitated an optimization of cross coupling procedures due to the great sterical hindrance of the ortho-substituent. The benz­amidines showed biological activity against factor Xa and selectivity against other serine proteases.

isosorbide - dianhydrohexitoles - amidines - Negishi reaction - factor Xa inhibitors

References

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<A NAME="RG14703ST-7A">7a</A>

General procedure for the preparation of bisamidines 3 and 4 from bisnitriles by the LiHMDS [6] method: A oven-dried Schlenck-flask equipped with a rubber septum is charged with HMDS (2.6 mmol) in THF (3 mL) under argon atmosphere and cooled by an ice bath. After addition of n-BuLi (3.0 mmol, 2.5 M in hexane) and stirring for 1 h a solution of the bisnitrile (0.52 mmol) in THF (3 mL) was added. The reaction mixture turned dark red or brown. It was stirred for 24 h at room temperature and then quenched with 6 M HCl in ethanol (2 mL). After 1 h the solvents were removed in vacuo. The residue was solved in few MeOH and purified by preparative HPLC (Rainin RP18, H₂O/CH₃CN mixtures with 0.1% TFA). The bisamidine was isolated as a TFA salt by lyophilization resulting in a colorless powder.

<A NAME="RG14703ST-7B">7b</A>

Analytical data of 3 and 4: 2-O-(4′-Amidinophenyl)-5-O-(3′′-amidinophenyl)-1,4:3,6-dianhydro-d-sorbitol trifluoroacetic acid salt (3):
[α]_D ²⁰ = +49, [α]₅₇₈ ²⁰ = +51, [α]₅₄₆ ²⁰ = +58, [α]₄₃₆ ²⁰ = +100, [α]₃₆₅ ²⁰ = +160 (c 0.099, H₂O); ¹H NMR (300 MHz, DMSO-d ₆) δ = 3.87-4.05 (m, 4 H, 1-H₂, 6-H₂), 4.61 (d, J = 4.1 Hz, 1 H, 3-H), 5.02-5.13 (m, 3 H, 2-H, 4-H, 5-H), 7.19-7.44 (m, 5 H, 2′-H, 6′-H, 2′′-H, 4′′-H, 6′′-H), 7.55 (t, J = 7.9 Hz, 1 H, 5′′-H), 7.79 (pd, J = 9.0 Hz, 2 H, 3′-H, 5′-H), 8.88-9.29 [m, 8 H, 2 × C(NH₂)₂]. ¹³C NMR (75 MHz, DMSO-d ₆) δ = 71.2, 72.7 (C-1, C-6), 77.4, 81.1, 81.5, 86.0 (C-2, C-3, C-4, C-5), 115.1 (C-2′′), 115.4 (C-2′, C-6′), 120.1 (C-4′), 120.8, 121.1 (C-4′′, C-6′′), 129.9 (C-3′′), 130.3 (C-3′, C-5′), 130.8 (C-5′′), 156.9 (C-1′′), 162.5 (C-1′), 164.9, 165.4 [2 × C(NH₂)₂]; HRMS (FAB): m/z calcd 383.1719, found 383.1717 (C₂₀H₂₃N₄O₄, M + H⁺). 2-O-(3′-Amidinophenyl)-5-O-(4′′-amidinophenyl)-1,4:3,6-dianhydro-d-sorbitol trifluoroacetic acid salt (4):
[α]_D ²¹ = +46, [α]₅₇₈ ²¹ = +49, [α]₅₄₆ ²¹ = +55, [α]₄₃₆ ²¹ = +94, [α]₃₆₅ ²¹ = +157 (c 0.267, H₂O); ¹H NMR (300 MHz, DMSO-d ₆) δ = 3.86-4.10 (m, 4 H, 1-H₂, 6-H₂), 4.60 (d, J = 4.7 Hz, 1 H, 3-H), 5.00-5.15 (m, 3 H, 2-H, 4-H, 5-H), 7.18 (pd, J = 9.0 Hz, 2H, 2′′-H, 6′′-H), 7.34-7.45 (m, 3 H, 2′-H, 4′-H, 6′-H), 7.53 (t, J = 7.9 Hz, 1 H, 5′-H), 7.83 (pd, J = 8.9 Hz, 2 H, 3′′-H, 5′′-H), 9.00-9.35 [m, 8 H, 2 × C(NH₂)₂]; ¹³C NMR (75 MHz, DMSO-d ₆) δ = 70.9, 72.8 (C-1, C-6), 77.3, 80.8, 81.6, 86.0 (C-2, C-3, C-4, C-5), 114.6 (C-2′), 115.7 (C-2′′, C-6′′), 120.5, 120.7 (C-4′, C-6′), 120.6 (C-4′′), 129.6 (C-3′), 130.6 (C-3′′, C-5′′), 158.0 (C-1′), 161.1 (C-1′′), 164.9, 165.5 [2 × C(NH₂)₂]; HRMS (FAB): m/z calcd. 383.1719, found 383.1715 (C₂₀H₂₃N₄O₄, M + H⁺).

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Coupling of boronic acid 19 using several Suzuki methods:

<A NAME="RG14703ST-14A">14a</A> Miyaura N. Suzuki A. Chem. Rev.  1995,  95:  2457 ; standard conditions: PdCl₂(PPh₃)₂, Bu₄NBr (cat.), aq. Na₂CO₃, PhMe reflux, 44%

<A NAME="RG14703ST-14B">14b</A> Wallow TI. Novak BM. J. Org. Chem.  1994,  59:  5034 ; Pd(OAc)₂, aq. Na₂CO₃, THF reflux, 0%

<A NAME="RG14703ST-14C">14c</A> Wolfe JP. Singer RA. Yang BH. Buchwald SL. J. Am. Chem. Soc.  1999,  121:  9550 ; Pd(OAc)₂, 2-(di-tert-butylphosphino)-biphenyl, KF, THF reflux, 0%

<A NAME="RG14703ST-14D">14d</A> Alo BI. Kandil A. Patil PA. Sharp MJ. Siddiqui MA. Snieckus V. J. Org. Chem.  1991,  56:  3763 ; Pd₂(dba)₃, PPh₃, aq. Na₂CO₃, DME reflux, 35%

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<A NAME="RG14703ST-15A">15a</A> Savage SA. Smith AP. Fraser CL. J. Org. Chem.  1998,  63:  10048 

<A NAME="RG14703ST-15B">15b</A>

Negishi coupling of aryl iodide 18: An oven-dried Schlenk-flask equipped with a rubber septum was charged with 1.29 g (6.0 mmol) PhSO₂NHt-Bu in 15 mL THF under an argon atmosphere and cooled in an ice bath. After addition of 8.2 mL n-BuLi (1.6 M in hexanes) the solution was stirred for 2 h. A thick, pale yellow precipitate formed. 1.82 g (13.4 mmol) ZnCl₂ beads were added (the precipitate dissolves) and 1 h later a solution of 2.19 g (5.0 mmol) 18, 185 mg (0.2 mmol) Pd₂(dba)₃ and 262 mg (1.0 mmol) PPh₃ in 10 mL THF was transferred into the reaction mixture. After addition of 424 mg (10.0 mmol) dried LiCl the reaction mixture was refluxed for 70 h. 100 mL sat. aq. NH₄Cl and 100 mL MTBE were added and the aqueous layer was extracted three times with MTBE. The combined organic fractions were washed with brine and dried over MgSO₄. Purification by flash chromatography (pentane/MTBE 2:1→1:1) yielded 2.18 g (4.2 mmol, 83%) pure 21.

<A NAME="RG14703ST-15C">15c</A>

Analytical data of 2-O-benzyl-5-O-[4′-(2′′-tert-butylamino-sulfonylphenyl)-phenyl]-1,4:3,6-dianhydro-d-mannitol (21): colorless solid; Mp 62 °C; [α]_D ²⁰ = +128, [α]₅₇₈ ²⁰ = +133, [α]₅₄₆ ²⁰ = +152 (c 1.008, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ = 0.98 [s, 9 H, C(CH₃)₃], 3.58 (s, 1 H, NH), 3.78 (t, J = 8.7 Hz, 1H, 1-H), 3.94 (dd, J = 8.6 Hz, 7.0 Hz, 1H, 1-H), 4.06-4.12 (m, 2 H, 2-H, 6-H), 4.20 (dd, J = 9.4 Hz, 6.0 Hz, 1 H, 6-H), 4.60 (d, J = 11.9 Hz, 1 H, CHHPh), 4.62 (t, J = 4.7 Hz, 1 H, 3-H), 4.78 (d, J = 11.9 Hz, 1 H, CHHPh), 4.79-4.85 (m, 2 H, 4-H, 5-H), 7.04 (pd, J = 8.7 Hz, 2H, 2′-H, 6′-H), 7.29 (dd, J = 7.7 Hz, 1.0 Hz, 1 H, 6′′′-H), 7.29-7.40 (m, 5 H, Ph-H), 7.43-7.47 (m, 3 H, 3′-H, 5′-H, 4′′′-H), 7.53 (td, J = 7.6 Hz, 1.2 Hz, 1H, 5′′′-H), 8.15 (dd, J = 7.9 Hz, 1.0 Hz, 1H, 3′′′-H); ¹³C NMR (75 MHz, CDCl₃) δ = 29.7 [C(CH₃)₃], 54.3 [C(CH₃)₃], 71.0, 71.6, 72.6 (C-1, C-6, CH ₂Ph), 77.9, 78.9, 80.6, 80.8 (C-2, C-3, C-4, C-5), 114.9 (C-2′, C-6′), 127.6, 128.1 (C-3′′, C-6′′), 127.9, 128.4 (Ph-C), 131.1 (C-3′, C-5′), 131.7, 132.4 (C-4′′, C-5′′), 132.2 (C-4′), 137.6 (Ph-C_q), 139.4 (C-1′′), 142.2 (C-2′′), 158.1 (C-1′); IR(film): 3371, 2973, 2876, 1607, 1514, 1467, 1324, 1245, 1152, 1128, 1076, 988, 834, 765 cm^-1; Anal. calcd. for C₂₉H₃₃NO₆S (523.65) C 66.52, H 6.35, N 2.68, found C 66.41, H 6.01, N 2.48.

<A NAME="RG14703ST-16A">16a</A> Judkins BD. Allen DG. Cook TA. Evans B. Sardharwala TE. Synth. Commun.  1996,  26:  4351 

<A NAME="RG14703ST-16B">16b</A>

Preparation of benzamidine 5 via amide oxime: Benzonitrile 23 (1 mmol) was dissolved in 10 mL THF/EtOH (1:1). After addition of NH₂OH·HCl (3 mmol), Na₂CO₃ (2 mmol) and 10 mL water the mixture was heated to 80 °C and stirred for 20 h (TLC monitoring). After cooling 20 mL water was added and the aqueous layer was extracted three times each with 20 mL CH₂Cl₂. The combined organic fractions were dried over MgSO₄ and the solvents were removed in vacuo. The crude amide oxime was then dissolved in 30 mL MeOH/HOAc (1:1) and Ac₂O (2 mmol) was added. After 30 min Pd/C was added and the reaction mixture was vigorously stirred under hydrogen atmosphere (HPLC monitoring, Rainin RP18, H₂O/CH₃CN mixtures + 0.1% TFA). Finally, the solution was filtrated over a pad of celite and the solvents were completely removed in vacuo. The crude bezamidine was then stirred under an argon atmosphere in dry TFA/anisole (10:1) for 24 h. Purification by flash chromatography (CH₂Cl₂/MeOH/TFA, 100:2:1 → 100:5:1), concentration of all product fractions and subsequent precipitation with MTBE/hexane gave 5 as TFA salt.

<A NAME="RG14703ST-16C">16c</A>

Analytical data of 2-O-(4′-amidinophenyl)-5-O-[4′′-(2′′′-aminosulfonylphenyl)-phenyl]-1,4:3,6-dianhydro-d-sorbitol trifluoroacetic acid salt (5): colorless solid; [α]_D ²⁰ = +51, [α]₅₇₈ ²⁰ = +54, [α]₅₄₆ ²⁰ = +61, [α]₄₃₆ ²⁰ = +108, [α]₃₆₅ ²⁰ = +174 (c 0.407, CH₂Cl₂/MeOH, 1:1); ¹H NMR (500 MHz, DMSO-d ₆) δ = 3.56 (d, J = 10.4 Hz, 1 H, 1-H), 3.89 (dd, J = 9.4 Hz, 5.4 Hz, 1 H, 6-H), 4.07 (dd, J = 9.4 Hz, 5.7 Hz, 1 H, 6-H), 4.11 (dd, J = 10.4 Hz, 3.8 Hz, 1 H, 1-H), 4.62 (d, J = 5.1 Hz, 1 H, 3-H), 4.97 (q, J = 5.5 Hz, 1 H, 5-H), 5.04 (t, J = 5.0 Hz, 1 H, 4-H), 5.11 (d, J = 3.3 Hz, 1 H, 2-H), 7.02 (pd, J = 8.7 Hz, 2 H, 2′′-H, 6′′-H), 7.13 (s, 2 H, SO₂NH₂), 7.20 (pd, J = 8.9 Hz, 2 H, 2′-H, 6′-H), 7.29 (d, J = 7.5 Hz, 1 H, 6′′′-H), 7.32 (pd, J = 8.7 Hz, 2 H, 3′′-H, 5′′-H), 7.53 (t, J = 7.5 Hz, 1 H), 7.59 (t, J = 7.4 Hz, 1 H, 4′′′-H, 5′′′-H), 7.83 (pd, J = 8.8 Hz, 2 H, 3′-H, 5′-H), 8.01 (d, J = 7.8 Hz, 1 H, 3′′′-H), 9.01/9.15 [s/s, 4 H, C(NH₂)₂]; ¹³C NMR (75 MHz, DMSO-d ₆) δ = 70.9, 71.7 (C-1, C-6), 77.1, 80.7, 81.8, 86.0 (C-2, C-3, C-4, C-5), 114.3 (C-2′′, C-6′′), 115.7 (C-2′, C-6′), 120.6 (C-4′), 127.4 (C-3′′′, C-6′′′), 130.5, 130.6 (C-3′, C-5′, C-3′′, C-5′′), 131.6, 132.7 (C-4′′, C-4′′′, C-5′′′), 139.8 (C-1′′′), 142.4 (C-2′′′), 157.3 (C-1′′), 161.2 (C-1′), 164.9 [C(NH₂)₂]; HRMS (ESI) m/z calcd. 496.1542, found 496.1544 (C₂₅H₂₆N₃O₆S, M + H⁺).

<A NAME="RG14703ST-17">17</A>

Pd/C is preferred, since the use of Raney-nickel in MeOH/AcOH leads to the formation of minor amounts of Ni(OAc)₂, which is difficult to remove by chromatography.

<A NAME="RG14703ST-18">18</A> Brougham P. Cooper MS. Cummerson DA. Heaney H. Thompson N. Synthesis  1987,  1015 

<A NAME="RG14703ST-19">19</A> Krone W. Chem. Ber.  1891,  24:  834