Fluorinated conformationally restricted gamma-aminobutyric acid aminotransferase inhibitors

Abstract

On the basis of the structures of several potent inhibitor molecules for gamma-aminobutryric acid aminotransferase (GABA-AT) that were previously reported, six modified fluorine-containing conformationally restricted analogues were designed, synthesized, and tested as GABA-AT inhibitors. The syntheses of all six molecules followed from a readily synthesized ketone intermediate. Three of the molecules were found to be irreversible inhibitors of GABA-AT with comparable or larger k(inact)/K(I) values than that of vigabatrin, a clinically used antiepilepsy drug, and the other three were reversible inhibitors. A possible mechanism for inactivation by one of the inactivators is proposed.

Figure 1

Vigabatrin (1) and conformationally-restricted analogues

Figure 2

New fluorinated conformationally-restricted potential inhibitors and inactivators of GABA-AT

Scheme 1

Reagents and conditions: a, PMBCl, NaH, Bu₄NI, DMF, 0 °C - r.t., 2h, 83%; b, DBDMH, HOAc, r.t., 20h, 97%; c, Bu₃SnH, AIBN, PhH, reflux, 12h, 95%; d, K₂CO₃, MeOH, H₂O, r.t., 2h, 87%; e, NMO, TPAP, DCM, r.t., 24h, 70%.

Scheme 2

Reagents and conditions: a, NH₂NH₂.H₂O, Et₃N, EtOH, reflux, 1 h; b, I₂, Et₃N, benzene, r.t., 2h; c, t-BuOK, ether, r.t., 20 h, 60% in three steps; d, Me₃SnSnMe₃, Pd(PPh₃)₄, PhMe, reflux, 30 min, 49%; e, XeF₂, AgOTf, 2,6-bis(tert-butyl)-4-methylpyridine, DCM, r.t., 8 min, 30%; f, CAN, CH₃CN, H₂O, r.t., 2 h, 55%; g, 4N HCl (aq.), 70 °C, 0.5-1 h, 64%

Scheme 3

Reagents and conditions: a, TMSRf, TBAF (cat.), THF, r.t., 1 h, 95%; b, TsCl, NaH, ether, 0 °C, 16 h, 79%.

Scheme 4

Reagents and conditions: a, MFSDA, CuI, DMF, HMPA, 20 h, 75%; b, CAN, MeCN/H₂O, r.t., 3 h, 61%; c, 4N HCl (aq.), 70 °C, 0.5-1 h, 85%.

Scheme 5

Reagents and conditions: a, CF₃CF₂SiMe₃/KF/CuI, NMO/DMF(1/1), 75 °C, 24 h, 57%; b, CAN, CH₃CN, H₂O, r.t., 2 h, 76%; c, 4N HCl (aq.), 70 °C, 0.5-1 h, 82%.

Scheme 6

Reagents and conditions: a, BrCH₂PPh₃.Br, tert-BuOK, THF, -78 C, 20 h, 72% E/Z; b, MFSDA, CuI, DMF, HMPA, 75 °C, 20 h, 95%; c, CAN, CH₃CN, H₂O, r.t., 2 h, 76%; d, 4N HCl (aq.), 70 °C, 10-12 h, 79%.

Scheme 7

Reagents and conditions: a, CBr₄, PPh₃, toluene, reflux, 22 h, 86%; b, MFSDA, CuI DMF, HMPA, 75 °C, 50 h, 82%; c, CAN, CH₃CN, H₂O, r.t., 1 h, 56%; d, 4N HCl (aq.), 70 °C, 10-12 h, 77%.

Scheme 8

Figure 3

Enzyme activity and fluoride ion release during inactivation of GABA-AT with 6 (2 mM) as a function of time. Fluoride ion concentration when GABA-AT was incubated with 6 (diamonds); fluoride ion concentration when human albumin was incubated with 6 (squares); remaining relative enzyme activity as compared to control when GABA-AT was incubated with 6 (triangles).

Figure 4

Enzyme activity and fluoride ion release during inactivation of GABA-AT with 7 (2 mM) as a function of time. Fluoride ion concentration when GABA-AT was incubated with 7 (diamonds); remaining relative enzyme activity as compared to control when GABA-AT was incubated with 7 (squares).