R. G. Bhat et al. / Tetrahedron Letters 44 (2003) 5251–5253
5253
the scope of these new reagents in the synthesis of cyclic
peptides.
Acknowledgements
We thank the DRDO, New Delhi, for financial support
of this investigation and the Foreign Ministry of France
for a Lavoisier grant to E.P.
Spectral data of selected compounds:
Dimethyl bis (N-benzyloxycarbonyl)-
L
-homocystine
1
(10c): H NMR (300 MHz, CDCl3, 25°C): l 7.35 (s,
10H, 2×Ph), 5.49 (d, 2H, 2×NH, J=7.5 Hz), 5.1 (s, 4H,
2×CH2Ph), 4.52–4.46 (m, 2H, 2×CH), 3.76 (s, 6H,
2×CH3), 2.70 (t, 4H, 2×CH2S, J=6.9 Hz), 2.30–2.17
(m, 2H, 2×[HCHa]CH), 2.11–2.0 (m, 2H, 2×
[HCHb]CH); 13C NMR (75.45 MHz, CDCl3, 25°C): l
172.3 (CO2CH3), 156.0 (NCO2), 136.0 (Ph), 128.5 (Ph),
128.2 (Ph), 128.1 (Ph), 67.1 (CH2Ph), 52.9 (OCH3),
52.6 (CH), 34.3 (CH2S), 32.3 (CH2CH); C26H32N2O8S2,
calcd mass: 564, FABMS m/z: 565 (MH)+.
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cystine (12c): H NMR (300 MHz, CDCl3, 25°C): l
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C26H32N2O8Se2, calcd mass: 660, FABMS m/z: 698
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Dimethyl bis (N-benzyloxycarbonyl)-
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1
(11c): H NMR (300 MHz, CDCl3, 25°C): l 7.35 (s,
10H, 2×Ph), 5.40 (d, 2H, 2×NH, J=7.8 Hz), 5.11 (s,
4H, 2×CH2Ph), 4.41–4.39 (m, 2H, 2×CH), 3.75(s, 6H,
2×CH3), 2.66–2.64 (m, 4H, 2×CH2S), 1.96–1.91 (m, 2H,
2×{HCHa}CH), 1.75 (m, 6H, 2×[CH2CH2CH and CH2
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128.2 (Ph), 128.1 (Ph), 67.0 (CH2Ph), 53.4 (OCH3),
52.5 (CH), 37.8 (CH2S), 31.3 (CH2), 24.7 (CH2CH);
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(MH)+.
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1
cystine (13c): H NMR (300 MHz, CDCl3, 25°C): l
7.35 (s, 10H, 2×Ph), 5.44 (d, 2H, 2×NH, J=8.1 Hz),
5.11 (s, 4H, 2×CH2Ph), 4.44–4.39 (m, 2H, 2×CH), 3.75
(s, 6H, 2×CH3), 2.86–2.82 (m, 4H, 2×CH2Se), 2.05–1.94
(m, 2H, 2×{HCHa}CH), 1.77 (m, 6H, 2×[CH2CH2CH
and CH2{HCHb}CH]); 13C NMR (75.45 MHz, CDCl3,
25°C): l 172.7 (CO2CH3), 155.9 (NCO2), 136.1 (Ph),
128.5 (Ph), 128.1 (Ph), 128.0 (Ph), 67.0 (CH2Ph), 53.3
(OCH3), 52.4 (CH), 32.2 (CH2Se), 28.5 (CH2), 26.5
(CH2CH); C28H36N2O8Se2, calcd mass: 688, FABMS
m/z: 689 (MH)+.