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the ligands are stable under the oxidation conditions. For
instance, system 5 was not oxidized under the reaction
conditions, suggesting that the deactivation of the metal
complex is not the result of ligand degradation. In contrast,
the bis(valine) complex 13, when submitted to the same
reaction conditions (3 equiv PhIO), led to complete degrada-
tion of the ligand segment yielding the cyclic urea derivative
14 as the major product (Scheme 4).[15]
À
[8] For pioneering work on selective intramolecular C H
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O
O
O
PhIO (3 equiv)
CH3CN (1 mM)
O
O
N
NH2
NH2
Mn
N
NH
O
O
N
50 % yield
H
13
14
[9] a) See reference [7]; b) W.-H. Leung, J.-X. Ma, V. W.-W.
Yam, C.-M. Che, C.-K. Poon, J. Chem. Soc. Dalton Trans.
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Scheme 4. Complete degradation of the bis(valine)manganese complex 13 in the
presence of iodosylbenzene.
[10] Experimental protocols for synthesis and oxidation of
complexes 1, 5, and 6 can be found in the Supporting
information.
The simplicity of covalently assembled models of this type
render them suitable probes for the rapid evaluation of novel
metal complexes with regard to their capability to function-
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À
alize C H bonds. We are currently studying possibilites for
predictable positioning of the substrate to the metal through
noncovalent recognition forces in order to attain a truly
catalytic oxidation species.
Received: October 27, 1999 [Z14192]
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Solid-Phase Synthesis of Unprotected
N-Glycopeptide Building Blocks for SPOT
Synthesis of N-linked Glycopeptides
Laurence Jobron and Gerd Hummel*
Several approaches to the chemical synthesis of N-linked
glycopeptides have been reported.[1] For the synthesis of
glycosylated amino acids, the carbohydrate moiety is usually
protected but unprotected glycosylamines have also been
used.[2, 3] Using unprotected glycosylamines generally results
in low yields[4, 5] and the compounds have to be purified by
column chromatography. We present here a new and efficient
method for the solid-phase synthesis of unprotected N-glyco-
peptide building blocks on a continous surface (SPOT syn-
thesis). SPOT synthesis on cellulose[6] is a highly effective
[*] Dr. G. Hummel, Dr. L. Jobron
Jerini Bio Tools GmbH
Rudower Chaussee 29, 12489 Berlin (Germany)
Fax : (49)30-6392-6395
Angew. Chem. Int. Ed. 2000, 39, No. 9
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0570-0833/00/3909-1621 $ 17.50+.50/0
1621