EPC Syntheses of Trifluorocitronellol and of Hexafluoropyrenophorin – A Comparison of Their Physiological Properties with the Nonfluorinated Analogs

Götzö, Stephan P.; Seebàch, Dieter; Sanglier, Jean‐Jacques

doi:10.1002/(sici)1099-0690(199910)1999:10<2533::aid-ejoc2533>3.0.co;2-o

Cited by 24 publications

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“…In a second approach (cf. B in Scheme 8), the aldol addition of the oxazolidinone derivatives III with aldehydes IV (PG' Tr [107]; PG' Ts [106]), followed by deoxygenation under Barton ± McCombie conditions [67] [108] [ 109], resulted in the isolation of degradation products caused by retro-aldol reactions, occurring during the deoxygenation step. Thus, the amidomethylation reaction via Ti-enolates was attempted (cf.…”

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Preparation of Protected β²‐ and β³‐Homocysteine, β²‐ and β³‐Homohistidine, and β²‐Homoserine for Solid‐Phase Syntheses

Lelais

Micuch

Josien‐Lefebvre

et al. 2004

Helvetica Chimica Acta

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The Ser, Cys, and His side chains play decisive roles in the syntheses, structures, and functions of proteins and enzymes. For our structural and biomedical investigations of b-peptides consisting of amino acids with proteinogenic side chains, we needed to have reliable preparative access to the title compounds. The two b 3homoamino acid derivatives were obtained by Arndt ± Eistert methodology from Boc-His(Ts)-OH and Fmoc-Cys(PMB)-OH (Schemes 2 ± 4), with the side-chain functional groups reactivities requiring special precautions. The b 2 -homoamino acids were prepared with the help of the chiral oxazolidinone auxiliary DIOZ by diastereoselective aldol additions of suitable Ti-enolates to formaldehyde (generated in situ from trioxane) and subsequent functional-group manipulations. These include OH 3 O t Bu etherification (for b 2 hSer; Schemes 5 and 6), OH 3 STrt replacement (for b 2 hCys; Scheme 7), and CH 2 OH 3 CH 2 N 3 3 CH 2 NH 2 transformations (for b 2 hHis; Schemes 9 ± 11). Including protection/deprotection/re-protection reactions, it takes up to ten steps to obtain the enantiomerically pure target compounds from commercial precursors. Unsuccessful approaches, pitfalls, and optimization procedures are also discussed. The final products and the intermediate compounds are fully characterized by retention times (t R ), melting points, optical rotations, HPLC on chiral columns, IR, 1 Hand 13 C-NMR spectroscopy, mass spectrometry, elemental analyses, and (in some cases) by X-ray crystalstructure analysis.

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Preparation of Protected β²‐ and β³‐Homocysteine, β²‐ and β³‐Homohistidine, and β²‐Homoserine for Solid‐Phase Syntheses

Lelais

Micuch

Josien‐Lefebvre

et al. 2004

Helvetica Chimica Acta

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4-Benzyloxybutanal

Brummond¹

2003

Encyclopedia of Reagents for Organic Synthesis

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The Barton‐McCombie Reaction

2012

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Deoxygenations of alcohols, i.e., processes that replace a hydroxyl group with hydrogen at a saturated carbon, find applications in both total synthesis and the systematic modifications of natural products. They may also be employed to introduce deuterium or tritium in a site‐specific manner. Reductive methods that involve ionic or highly polarized reagents or intermediates can be limited in their applicability: for example, competing reaction pathways including cationic rearrangements and anionic eliminations may be encountered in sterically hindered systems with substrates bearing heteroatoms close to the center undergoing reduction. As evidenced by developments over the last few decades, methods that involve the generation and direct quenching via hydrogen atom abstraction of the derived, carbon‐centered radical typically show the greatest tolerance for the presence of other functional groups and for variations in both the steric acid and the electronic environment in the vicinity of the center undergoing deoxygenation. Derivatization of the hydroxyl is a prerequisite, the determinant factors for efficient formation of the deoxygenated product lies in the ability of the combination of the substrate and reagents to induce homolysis of the C‐O bond coupled with the induction of homolysis to rapidly reduce a free radical by hydrogen donation, thereby propagating an efficient chain process. A high‐yielding way to realize this sequence was first described by Barton McCombie using the free‐radical chain reaction of O ‐thioacyl derivatives of secondary alcohols with tri‐ n ‐butylstannane. This chapter provides a detailed description and comparison of the combinations of substrates and reagents that will bring about these processes and provides a summary and evaluation of alternative deoxygenation methods. Mechanistic and stereochemical issues set out the scope and limitations of these processes with respect to both the thioacylation and reduction steps and exemplify some applications to both total synthesis and the modification of natural products.

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EPC Syntheses of Trifluorocitronellol and of Hexafluoropyrenophorin – A Comparison of Their Physiological Properties with the Nonfluorinated Analogs

Cited by 24 publications

References 32 publications

Preparation of Protected β²‐ and β³‐Homocysteine, β²‐ and β³‐Homohistidine, and β²‐Homoserine for Solid‐Phase Syntheses

Preparation of Protected β²‐ and β³‐Homocysteine, β²‐ and β³‐Homohistidine, and β²‐Homoserine for Solid‐Phase Syntheses

4-Benzyloxybutanal

The Barton‐McCombie Reaction

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EPC Syntheses of Trifluorocitronellol and of Hexafluoropyrenophorin – A Comparison of Their Physiological Properties with the Nonfluorinated Analogs

Cited by 24 publications

References 32 publications

Preparation of Protected β2‐ and β3‐Homocysteine, β2‐ and β3‐Homohistidine, and β2‐Homoserine for Solid‐Phase Syntheses

Preparation of Protected β2‐ and β3‐Homocysteine, β2‐ and β3‐Homohistidine, and β2‐Homoserine for Solid‐Phase Syntheses

4-Benzyloxybutanal

The Barton‐McCombie Reaction

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Preparation of Protected β²‐ and β³‐Homocysteine, β²‐ and β³‐Homohistidine, and β²‐Homoserine for Solid‐Phase Syntheses

Preparation of Protected β²‐ and β³‐Homocysteine, β²‐ and β³‐Homohistidine, and β²‐Homoserine for Solid‐Phase Syntheses