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741.
Wehlan H Dauber M Fernaud MT Schuppan J Keiper S Mahrwald R Garcia ME Koert U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(28):7378-7397
The total synthesis of apoptolidin A is described employing an early glycosylation strategy. Strategic disconnections were chosen between C11-C12 (cross-coupling) and C19O-C1 (macrocyclization). The cis-selective glycosylation at C9-OH was achieved with the new SIBA protective group at O2/O3 of the L-glucose residue. Auxiliary substitutents at the 2-position of the 2-deoxy sugars were applied to form selectively the glycosidic linkages of the C27 disaccharide. The cross-coupling of the glycosylated northern half with the glycosylated southern half was achieved with CuI-thiophene carboxylate. The macrocyclization of a trihydroxy carboxylic acid produced the 20-membered macrolide selectively. H2SiF6 was suitable for the final deprotection of the silyl ethers and the conversion of the C21 methylketal into the hemiketal. The synthetic flexibility of the approach was proven by the synthesis of some glycovariants. 相似文献
742.
Schuppan J Wehlan H Keiper S Koert U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(28):7364-7377
An efficient stereocontrolled synthesis of apoptolidinone A, the aglycone of apoptolidin A is described. The synthetic strategy relies on a cross coupling between C11/C12 of a northern half (C1-C11) and a southern part (C12-C28) followed by a ring-size selective macrolactonization. Key steps for the introduction of the southern half stereocenters are a stereoselective aldol reaction, a substrate controlled dihydroxylation and a chelation-controlled Grignard/aldehyde addition. The conjugated triene of the northern half was built up successively by E-selective Wittig reactions. L-Malic acid was chosen as the chiral pool source for the C8/C9 stereocenters. The final cleavage of the silyl ethers and the conversion of the C21 methyl ketal into the hemiketal was achieved by HF.pyridine. 相似文献
743.
Sonja Peters Ewoud van Velzen Hans-Gerd Janssen 《Analytical and bioanalytical chemistry》2009,394(5):1273-1281
In chromatographic profiling applications, peak alignment is often essential as most chromatographic systems exhibit small
peak shifts over time. When using currently available alignment algorithms, there are several parameters that determine the
outcome of the alignment process. Selecting the optimum set of parameters, however, is not straightforward, and the quality
of an alignment result is at least partly determined by subjective decisions. Here, we demonstrate a new strategy to objectively
determine the quality of an alignment result. This strategy makes use of a set of control samples that are analysed both spiked
and non-spiked. With this set, not only the system and the method can be checked but also the quality of the peak alignment
can be evaluated. The developed strategy was tested on a representative metabolomics data set using three software packages,
namely Markerlynx™, MZmine and MetAlign. The results indicate that the method was able to assess and define the quality of
an alignment process without any subjective interference of the analyst, making the method a valuable contribution to the
data handling process of chromatography-based metabolomics data. 相似文献
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