Linear Trifluoroethylamine RGD Peptidomimetics: Stereoselective Synthesis and Integrin α_vβ₃ Affinity

Abstract

The Arg-Gly-Asp (RGD) tripeptide is the smallest recognition sequence for the α_vβ₃ integrin receptor. A number of nonpeptide analogues of the RGD linear sequence, some of them having improved pharmacological properties, have been proposed in the last two decades. In this study, the stereogenic trifluoroethylamine function was employed as peptide bond surrogate for the development of a new class of RGD peptide mimics. In fact, the trifluoroethylamine group was shown to behave as a peptide-bond surrogate maintaining the H-bond donor capacity of the NH peptide group and a CH(CF₃)NH backbone angle close to the native peptide bond 120°. The trifluoroethylamine function is also known to display high metabolic stability and in some cases it positively affects ligand–receptor interactions. Two linear Ψ[CH(CF₃)NH]Gly-RGD diastereoisomers were synthesized with good stereocontrol and submitted to biological assays. A remarkable loss in α_vβ₃ integrin affinity was observed for both compounds, suggesting that the bulky CF₃ moiety is not well tolerated within the α_vβ₃ binding pocket.

Key words

trifluoroethylamine - peptidomimetics - RGD - integrins

• References and Notes

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• 12 Aza-Michael Reaction of 1 with 2 To a stirred solution of 2 (1 mmol, 141 mg) and 1 (0.67 mmol, 189 mg) in dry toluene (10 ml) at r.t., DIPEA (0.74 mmol, 126 μL) was added. After 30 min at r.t. the mixture was concentrated, dissolved in EtOAc, and washed with 1 M HCl. The organic layers were dried over anhyd Na₂SO₄ and concentrated at reduced pressure. The crude was purified by flash chromatography (hexane–Et₂O = 9:1) affording 166 mg (64% yield) of the two pure diastereoisomers 3b and 3a in a 5:1 ratio. Compound 3b (major diastereoisomer): ¹H NMR (400 MHz, CDCl₃): δ = 4.72–4.62 (m, 2 H), 4.10–4.01 (m, 1 H), 3.70–3.62 (m, 1 H), 2.70–2.63 (dd, J = 16.2, 4.3 Hz, 1 H), 2.59–2.53 (dd, J = 16.2, 7.5 Hz, 1 H), 2.44–2.37 (m, 1 H), 1.45 (s, 18 H). ¹³C NMR (100 MHz, CDCl₃): δ = 172.26, 170.00, 124.70 (q, J = 284.3 Hz), 82.70, 81.72, 74.55, 58.09 (q, J = 30.1 Hz), 58.04, 40.15, 28.14, 28.04. ¹⁹F NMR (376 MHz, CDCl₃): δ = –75.31 (d, J = 7.2 Hz). ESI-MS: m/z calcd for C₁₅H₂₅F₃N₂O₆ [M + H]⁺: 387.2; found: 387.2. Compound 3a (minor diastereoisomer): ¹H NMR (400 MHz, CDCl₃): δ = 4.58 (dd, J = 13.2, 4.2 Hz, 1 H), 4.40 (dd, J = 13.2, 9.1 Hz, 1 H), 4.20–4.10 (m, 1 H), 3.68–3.76 (m, 1 H), 2.59 (dd, J = 16.5, 4.1 Hz, 1 H), 2.45 (dd, J = 16.5, 7.9 Hz, 1 H), 2.53–2.59 (m, 1 H), 1.46 (s, 9 H), 1.45 (s, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 171.72, 169.97, 124.99 (q, J = 285.2 Hz), 82.66, 81.57, 74.63, 58.08 (q, J = 29.1 Hz), 58.09 (q, J = 30.1 Hz), 57.01, 40.40, 28.17, 28.01. ¹⁹F NMR (376 MHz, CDCl₃): δ = –74.33 (d, J = 6.9 Hz). ESI-MS: m/z calcd for C₁₅H₂₅F₃N₂O₆ [M + H]⁺: 386.2; found: 386.2.
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• 16 RGD Mimic 8 ¹H NMR (400 MHz, D₂O): δ = 4.80–4.78 (m, 1 H), 4.31–4.28 (m, 1 H), 3.94 (t, J = 5.7 Hz, 1 H), 3.72–3.60 (m, 2 H), 3.51 (dd, J = 13.9, 6.4 Hz, 1 H), 3.22 (t, J = 6.7 Hz, 2 H), 2.50 (s, 3 H), 1.92–1.83 (m, 1 H), 1.78–1.57 (m, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 175.69, 174.65, 174.4, 162.94 (q, J = 35.4 Hz), 156.73, 125.29 (q, J = 282.4 Hz), 116.32 (q, J = 291.6 Hz), 57.49 (q, J = 27.5 Hz), 56.56, 53.56, 40.44, 37.64, 36.97, 28.04, 24.38, 21.67. ¹⁹F NMR (376 MHz, D₂O): δ = –74.15 (d, J = 7.2 Hz), –75.58 (s). ESI-MS: m/z calcd for C₁₅H₂₅F₃N₆O₆ [M + H]⁺: 443.2; found: 443.2. RGD Mimic 9 ¹H NMR (400 MHz, D₂O): δ = 4.80–4.78 (m, 1 H), 4.28–4.25 (m, 1 H), 4.04 (t, J = 6.1 Hz, 1 H), 3.71–3.60 (m, 2 H), 3.55–3.50 (m, 1 H), 3.21 (t, J = 6.7 Hz, 2 H), 2.93 (dd, J = 17.1, 5.3 Hz, 1 H), 2.83 (dd, J = 17.1, 6.9 Hz, 1 H), 2.04 (s, 3 H), 1.89–1.80 (m, 1 H), 1.77–1.55 (m, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 175.13, 174.4, 162.92 (q, J = 35.5 Hz), 156.72, 125.08 (q, J = 283.0 Hz), 116.30 (q, J = 291.7 Hz), 57.26 (q, J = 27.9 Hz), 55.97, 53.59, 40.41, 37.17, 36.72, 28, 24.36, 21.62. ¹⁹F NMR (376 MHz, D₂O): δ = –73.92 (d, J = 7.1 Hz), –75.59 (s). ESI-MS: m/z calcd for C₁₅H₂₅F₃N₆O₆ [M + H]⁺: 443.2; found: 443.2.
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