Partial thioamide scan on the lipopeptaibiotic trichogin GA IV. Effects on folding and bioactivity

• Marta De Zotti,
• Barbara Biondi,
• Cristina Peggion,
• Matteo De Poli,
• Haleh Fathi,
• Simona Oancea,
• Claudio Toniolo and
• Fernando Formaggio

Beilstein J. Org. Chem. 2012, 8, 1161–1171, doi:10.3762/bjoc.8.129

• Gly) residues spread across its sequence, which allows one to design suitable segments each with an achiral residue at its C-terminus, thus reducing dramatically the usually considerable risk of epimerization during the coupling reactions. For the best choice of the step involving treatment with the

Synthesis of highly functionalized β-aminocyclopentanecarboxylate stereoisomers by reductive ring opening reaction of isoxazolines

• Melinda Nonn,
• Loránd Kiss,
• Reijo Sillanpää and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2012, 8, 100–106, doi:10.3762/bjoc.8.10

• formed, then separated and isolated. The cycloaddition of nitrile oxide to trans-ethyl 2-aminocyclopent-3-enecarboxylate under similar conditions proceeded selectively with the formation of 6. Epimerization of 2 and 4 afforded trans derivatives 3 and 5 [48][49]. Since isoxazoline-functionalized molecules

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

• Kristina Butković,
• Željko Marinić,
• Krešimir Molčanov,
• Biserka Kojić-Prodić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

• photoproduct 12 from the trans configuration, although the formation of 12 via epimerization of 11 could not be eliminated. It is also evident that there are several competitive processes, which are summarized in Scheme 5. On irradiation of 3a (trans) or 3b (cis) parallel competitive processes are in operation

Asymmetric synthesis of quaternary aryl amino acid derivatives via a three-component aryne coupling reaction

• Elizabeth P. Jones,
• Peter Jones,
• Andrew J. P. White and
• Anthony G. M. Barrett

Beilstein J. Org. Chem. 2011, 7, 1570–1576, doi:10.3762/bjoc.7.185

• exposure to 0.5 M HCl, epimerization of the isopropyl group at C-3 occurs in near quantitative yield, giving adduct 13 (Scheme 10). The electron-withdrawing effect of the carbonyl moiety must increase the acidity of the C-3 proton to such an extent that the acidic media simply epimerizes at this center to

• . Hydrolysis to amino acids. Hydrolysis of analogue 6j. Epimerization at C-3 of 6g. Formation of quaternary Schöllkopf adducts employing a range of electrophiles. Supporting Information Supporting Information File 285: Detailed experimental procedures and analytical data for compounds 6a–j, 7b–c, 8a, 8d, 8e

Coupled chemo(enzymatic) reactions in continuous flow

• Ruslan Yuryev,
• Simon Strompen and
• Andreas Liese

Beilstein J. Org. Chem. 2011, 7, 1449–1467, doi:10.3762/bjoc.7.169

• catalyzed the epimerization of 14 yielding the epimer N-acetylmannosamine (15), which consequently was condensed by the second enzyme aldolase with pyruvic acid (16) to form the product 17 (Scheme 6). By appropriately adjusting the reaction parameters, such as pH, temperature and substrate concentrations

High chemoselectivity in the phenol synthesis

• Matthias Rudolph,
• Melissa Q. McCreery,
• Wolfgang Frey and
• A. Stephen K. Hashmi

Beilstein J. Org. Chem. 2011, 7, 794–801, doi:10.3762/bjoc.7.90

• -catalyzed conversion of the pure isomers. From the NMR spectra taken during the conversion (Figure 4), it could be clearly seen that no epimerization of the propargylic position occurred. In addition to the selective transformation to the phenols 37a and 37b as the main reaction products, partial removal of

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• is sometimes incomplete. This may arise due to a competitive gold-promoted cyclopropyl ring opening/epimerization/ring closure, both in cis and trans-cyclopropyl settings, which competes with the cyclization event, thus eroding the overall transfer of stereochemical information. Conclusion From the

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• with the corresponding amino acids or by the Nefkens procedure [9]. The latter procedure yields enantiomerically pure products (by optical rotation), whereas the thermal method leads to partial epimerization. Photochemistry of the tyrosine and histidine derivatives 8 and 9 The colorless phthalimides

Addition of lithiated enol ethers to nitrones and subsequent Lewis acid induced cyclizations to enantiopure 3,6-dihydro-2H-pyrans – an approach to carbohydrate mimetics

• Fabian Pfrengle and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, No. 75, doi:10.3762/bjoc.6.75

• ). We presume that an initially formed nitrone 22 probably undergoes base induced epimerization to generate the thermodynamically more stable trans-substituted nitrone 21. As shown below, the nitrone moiety of 21 can be regarded as a masked hydroxylamine, however, it should also be very useful for

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Synthesis and binding studies of two new macrocyclic receptors for the stereoselective recognition of dipeptides

• Ana Maria Castilla,
• M. Morgan Conn and
• Pablo Ballester

Beilstein J. Org. Chem. 2010, 6, No. 5, doi:10.3762/bjoc.6.5

• peptide-coupling reaction of the all-S linear tetrapeptide. As discussed above, one of the two diastereoisomers is probably the outcome of the epimerization reaction experienced by the stereogenic center in the α-position with respect to the carboxylic group undergoing activation. Likewise, the two minor

• peaks should correspond to cyclic diastereoisomers formed from macrocyclization and concomitant epimerization reactions experienced by the minor linear tetrapeptide S,S,S,R also incorporated into the starting material. Figure 4b depicts the HPLC chromatogram obtained from the analysis of the purified

• techniques. Initially, we used HBTU/NMM [25][33][34] for activation of the intramolecular peptide bond formation. We observed considerable epimerization at the stereogenic α-carbon. We assessed the coupling reaction using different coupling methods, HATU/NMM [35] and PyAOP/DIEA [36], and found that although

An enantiomerically pure siderophore type ligand for the diastereoselective 1 : 1 complexation of lanthanide(III) ions

• Markus Albrecht,
• Olga Osetska,
• Thomas Abel,
• Gebhard Haberhauer and
• Eva Ziegler

Beilstein J. Org. Chem. 2009, 5, No. 78, doi:10.3762/bjoc.5.78

• group for the attachment of other units. Coupling of 2 with three equivalents of 3 results in the formation of the ligand precursor 4. The triple Claisen rearrangement of 4 proceeds at 165 °C under inert atmosphere (N2) within 6 hours [36]. No epimerization occurs at the chiral carbon atoms of the

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

Highly brominated anthracenes as precursors for the convenient synthesis of 2,9,10-trisubstituted anthracene derivatives

• Osman Cakmak,
• Leyla Aydogan,
• Kiymet Berkil,
• Ilhami Gulcin and
• Orhan Buyukgungor

Beilstein J. Org. Chem. 2008, 4, No. 50, doi:10.3762/bjoc.4.50

• effective and convenient method to prepare hexabromide 3. Most of the product precipitated during the reaction. After the reaction, a rapid and simple recrystallization gave the pure hexabromide 3 in 95% yield. As hexabromide 4 is quite sensitive to daylight and temperature, aromatization and epimerization

Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis

• Roger Hunter,
• Sophie C. M. Rees-Jones and
• Hong Su

Beilstein J. Org. Chem. 2007, 3, No. 38, doi:10.1186/1860-5397-3-38

• under acid conditions with CAN to give lactam 10 in 82% yield with retention of the MOM groups (Scheme 4). The vinyl ether 10 was then converted to a ketal in order to preclude any epimerization occurring at C-4, and this was achieved by subjecting 10 to bromine in the presence of methanol to give

Reactions of glycidyl derivatives with ambident nucleophiles; part 2: amino acid derivatives

• Gerald Dyker,
• Andreas Thöne and
• Gerald Henkel

Beilstein J. Org. Chem. 2007, 3, No. 28, doi:10.1186/1860-5397-3-28

• the cyclization process the α-proton of the amino acid moiety is obviously acidic enough to allow epimerization at this centre. This is in accord with the exclusive formation of a single diastereoisomer of 9 and with the occurrence of 10a as a byproduct in up to 28 % yield, when the reaction was

8-epi-Salvinorin B: crystal structure and affinity at the κ opioid receptor

• Thomas A. Munro,
• Katharine K. Duncan,
• Richard J. Staples,
• Wei Xu,
• Lee-Yuan Liu-Chen,
• Cécile Béguin,
• William A. Carlezon Jr. and
• Bruce M. Cohen

Beilstein J. Org. Chem. 2007, 3, No. 1, doi:10.1186/1860-5397-3-1

• 02138, USA Department of Pharmacology, Temple University, 3420 N. Broad Street, Philadelphia, PA 19140, USA 10.1186/1860-5397-3-1 Abstract There have been many reports of epimerization of salvinorins at C-8 under basic conditions, but little evidence has been presented to establish the structure of

• these compounds. We report here the first crystal structure of an 8-epi-salvinorin or derivative: the title compound, 2b. The lactone adopts a boat conformation with the furan equatorial. Several lines of evidence suggest that epimerization proceeds via enolization of the lactone rather than a

• -salvinorin A (1b).[12] Brown also reported that deacetylation of 1a under basic conditions gave 8-epi-salvinorin B (2b), but did not characterize either compound. Several further reports of epimerization at C-8 appeared over the following decade, [13][14] but no characterization data was presented. Valdés