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References and notes
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12. (S)-MPBrG was obtained from the corresponding hydan-
toin, see: Courvoisier, L.; Ndzie, E.; Petit, M.-N.; Hedt-
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13. Typical procedure for asymmetric electrophilic fluorination
of a dipeptide. To a solution of Phth–Aib–(N-Me–Phg)–
OBn (0.15 mmol, 70.6 mg) at À78 °C in THF (1 mL),
LiHMDS (1 M in THF, 0.3 mmol) was added dropwise.
After 30 min the fluorinating reagent (F–pClBzQN–BF4,
0.165 mmol, 96.8 mg) was added in portions. The mixture
was stirred at À78 °C for 3 h and then hydrolyzed with a
saturated solution of NH4Cl. THF was evaporated and
the product extracted in CH2Cl2, then washed with a
saturated solution of NaHCO3, dried over MgSO4 and
concentrated. The residue was purified by chromatogra-
phy over silica gel to afford the fluorinated dipeptide in
88% yield; HPLC: Chiralcel OD-H, hexane–iPrOH 80:20,
1 mL/min, t1 = 14.3 min, t2 = 16.5 min. 19F NMR
(282 MHz, CDCl3): d = À138.4; 1H NMR (300 MHz,
CDCl3): d = 1.86 (s, 3H), 1.88 (s, 3H), 2.67 (d, 3H,
J = 1.2 Hz), 5.19 (d, 1H, J = 12.3 Hz), 5.30 (d, 1H,
J = 12.3 Hz), 7.25–7.38 (m, 8H), 7.58–7.61 (m, 2H),
7.74–7.77 (m, 2H), 7.85–7.89 (m, 2H); 13C NMR
(75 MHz, CDCl3): d = 24.9, 25.2, 32.9, 61.4, 67.7, 100.7
(d, J = 220.7 Hz), 123.5, 126.6, 127.0, 128.5, 128.6, 128.7,
129.6, 131.5, 134.2 (d, J = 27.3 Hz), 134.5, 135.5, 166.3 (d,
J = 26 Hz), 167.8, 174.4 (d, J = 1.3 Hz); HRMS Calcd for
C28H25FN2O5 [M] 488.1748. Found 488.1750.
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