Yield (Scheme 2). Scheme 2. Deprotection of TMS and Bn GroupsFigure 2. Preferred silyl
Yield (Scheme two). Scheme two. Deprotection of TMS and Bn GroupsFigure two. Preferred silyl etheracetate exchange of Neu5Ac: C4 (2 C9 (1 C8 (2 C2 (anomeric).Neu5Ac ReSET revealed completely diverse regioselectivity than previous work with pyranose sugars.16,17 In aldohexoses, the major C6 commonly exchanges first followed by the anomeric C1. Right after C1 exchange, C2 is usually subsequent to react then further exchange happens within a sequential manner around the pyranose ring. Witschi and co-workers also performed ReSET on N-acetyl glucosamine (GlcNAc), which can be an aldose sugar structurally comparable to Neu5Ac in terms of bearing an NHAc group. In that case, the first exchange also occurred in the PARP15 Formulation primary C6 instead of the anomeric position, which was proximal to the amide.16 The presence of NHAc in two presumably pulls electron density from the C4 O-Si bond, which makes it possible for for exchange to happen initially at C4 in favor with the principal C9 position. Additionally, the presence of methylene protons at C3 assures a less sterically hindered environment than what exactly is identified in prevalent pyranose sugars. Once C9 is acetylated, C8 is the subsequent to react. Once again, the electronic effect with the C9 ester group tends to make the C8 O-Si bond most susceptible to attack. The observation of C8 exchange in favor of the anomeric silyl ether group indicates that the quaternaryIn pursuit with the synthesis of Neu4,5,7,eight,9(Ac)five (15), compound four was selectively deprotected to expose the C7 and C8 diol (11, Scheme three). The anomeric silyl protecting group remained in tact presumably because of steric hindrance. Subjecting 11 to 1.5 equiv acetic anhydride gave selective acetylation of C7 (12), though excess acetic anhydride gave 13 (Scheme 3). Upon hydrogenolysis of 12, acyl migration from the 7-O-acetyl towards the C8 position occurred affording compound 9. Attempts to prevent migration employing different catalysts like palladium (98 ), palladium hydroxide, platinum(IV) oxide, and Raney nickel were unsuccessful. C7 to C8 acyl migration occurred under all situations, suggesting the C-8 acetate is actually a thermodynamic sink. Meanwhile, 13 was Nav1.5 drug subjected to hydrogenation to get rid of the anomeric silyl and benzyl groups to afford naturally occurring 15 in 92 yield. This route permitted for an alternative synthesis of 15, which had been previously synthesized.dx.doi.org10.1021ol502389g | Org. Lett. 2014, 16, 5044-Organic Letters Scheme three. Option Synthetic Route to Neu4,five,7,8,9(Ac)LetterAUTHOR INFORMATIONCorresponding Author(530) 754-6915. Tel: (530) 754-9557. E-mail: jgervayhagueucdavis.edu.NotesThe authors declare no competing economic interest.ACKNOWLEDGMENTS This work is supported by the National Institutes of Health, NIH Grant No. R01GM090262. NSF CRIF system (CHE 9808183), NSF Grant No. OSTI 97-24412, and NIH Grant No. RR11973 offered funding for the NMR spectrometers used on this project. We thank Dr. Jerry Dallas (University of California, Davis) for support with the long-range HMBC NMR experiments and 2D NMR experiments.
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