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Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

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esin column (Bio-Rad AGa 10x4 10-20 mesh, chloride fonn converted to hydroxide<br />

fom by prewashing with 4N NaOH then rinsed with Millipore Milli-Q Hz0 until the<br />

rinsings appeared neutral. larger column lengths were required to accommodate the CQ"<br />

generated). ZN AcOH or 1N fonnic acid was used to elute the amino acid <strong>and</strong> the eluant<br />

reduced in volume then lyophilized to dryness to give 45 mg (52%) <strong>of</strong> a white, powdery<br />

solid. Recrystallization from H20/acetone gave 19 mg (218) <strong>of</strong> colourless crystals.<br />

HPLC analysis perfarmed as described in 2.4.15a (linear gradient 5050 30mM sodium<br />

acetate: MeOH over 60 min) eluted the diastereomer formed from the L-arnino acid at<br />

42.5 min <strong>and</strong> the D-amino acid at 43.9 min to indicate 99% ee.<br />

mp 195- 198°C (dec); TLC (1 : 1 : 1 : 1, EtOAc:nBuOH:MeOH:H20) Rr = 0.48; 'H NMR<br />

p20, 250 MHz) 8 3.61 (s, lH, a-CH), 1.35 (s, 3H, p-CH3), 1.1 1 (s, 3H. p-CH3); I3c<br />

NMR @20,63 MHz) 6 176.1 (ÇOZH), 73.6 (BQ, 63.3 (a--, 30.7 @-CH3), 26.3 (P-<br />

- CH3); ESI-MS (M + H+) 133.93.<br />

2.4.23 Deprotection <strong>of</strong> Boe-Thr(Et)OBO ester 2.58: (2S,3R)-2-amho-3lydroxy-l<br />

methylpentanoic acid, 2-60,<br />

Boc-Thr(Et)OBO ester 2.58 (0.151 g, 0.46 mrnol) was deprotected as described in<br />

procedure 2.4.21 <strong>and</strong> lyophilized to give 37 mg (56%) <strong>of</strong> a white powder which was<br />

recrystallized from H20/acetone to give 15 mg (22%) <strong>of</strong> colourless crystals. HPLC<br />

analysis perfonned as descnbed in 2.4.15a (iinear gradient to 80:20 30mM sodium

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