Natural product biosyntheses in cyanobacteria: A treasure trove of unique enzymes

• Jan-Christoph Kehr,
• Douglas Gatte Picchi and
• Elke Dittmann

Beilstein J. Org. Chem. 2011, 7, 1622–1635, doi:10.3762/bjoc.7.191

• in the alternative epimer formation [32]. The CyrJ protein is the candidate protein for the sulfatation tailoring step. Anabaenopeptin Anabaenopeptins 5 are a highly diverse family of cyclic hexapeptides produced by various genera of freshwater cyanobacteria. Several members of the family potently

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

Efficient syntheses of 25,26-dihydrodictyostatin and 25,26-dihydro-6-epi-dictyostatin, two potent new microtubule-stabilizing agents

• María Jiménez,
• Wei Zhu,
• Andreas Vogt,
• Billy W. Day and
• Dennis P. Curran

Beilstein J. Org. Chem. 2011, 7, 1372–1378, doi:10.3762/bjoc.7.161

• ) and used it to prepare two new analogs: 16-desmethyl-25,26-dihydrodictyostatin (2a) and its C6 epimer 2b (Figure 1) [29]. The terminal C25–C26 alkene of the C23–C26 diene is a synthetic liability, so it was welcome news when the biological data revealed that the analogs lacking this alkene retained

• with 15 equiv of CrCl2, 0.2 equiv of NiCl2(dppf) and 15 equiv of 4,4'-di-tert-butyl-2,2'-dipyridine [47]. The target product 26b for the C6 (S)-series was obtained in respectable yield (42%). Only the target C9-β epimer was detected in the 1H NMR spectrum of the crude product, though we cannot rule out

• the presence of small amounts of the α-epimer. However, in the C6 (R)-series, the C9 β/α ratio was only about 75/25 and the isolated yield of pure β-epimer 26a was only 22%. After surveying several other conditions and solvents, we found that treatment of 4a with 15 equiv of CrCl2 and 0.2 equiv of

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• afforded the hemiacetal after spontaneous cyclization. Subsequent oxidation and deprotection afforded the desired compound. In the same paper, the total synthesis of the naturally occurring epimer of Penifulvin B (Penifulvin C) was described, which was achieved by replacing the trans-olefin by the cis

Design and synthesis of a cyclitol-derived scaffold with axial pyridyl appendages and its encapsulation of the silver(I) cation

• Pierre-Marc Léo,
• Christophe Morin and
• Christian Philouze

Beilstein J. Org. Chem. 2010, 6, 1022–1024, doi:10.3762/bjoc.6.115

• epimers 5 and 7 the dihedral angles of the proton geminal to the hydroxy group with vicinal protons are similar), the 1H- and 13C NMR spectra of 7 clearly differ from those of its epimer. Compounds 5 and 7 were also acetylated (to 8 and 9, respectively) and the chemical shift of the acetyl methyl group of

Chemical synthesis using enzymatically generated building units for construction of the human milk pentasaccharides sialyllacto-N-tetraose and sialyllacto-N-neotetraose epimer

• Dirk Schmidt and
• Joachim Thiem

Beilstein J. Org. Chem. 2010, 6, No. 18, doi:10.3762/bjoc.6.18

• derivatives. Keywords: block synthesis; human milk oligosaccharides; sialyllacto-N-neotetraose epimer; sialyllacto-N-tetraose; trisaccharide thioglycoside donors; Introduction From an inspection of contemporary syntheses of biologically and medicinally relevant oligosaccharides, it is evident that the

• , sialyllacto-N-tetraose (1) and an epimer of sialyllacto-N-neotetraose (2) (Figure 1) were selected as target molecules. Both these pentasaccharides, Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4Glc (1) and Neu5Acα2-6Galβ1-4GlcNAcβ1-4Galβ1-4Glc (2), are dominant constituents of complex human milk oligosaccharides (Figure

• a down field shifted doublet for H-4′ at δ 5.37 (J3′4′ = 2.9 Hz). A similar approach was employed for the synthesis of the protected epimer of sialyllacto-N-neotetraose 14. β-Galactosylation of 2-azidothioglucoside with p-nitrophenyl β-galactopyranoside and β-galactosidase (Bacillus circulans) gave

A short stereoselective synthesis of (+)-(6R,2′S)-cryptocaryalactone via ring- closing metathesis

• Palakodety Radha Krishna,
• Krishnarao Lopinti and
• K. L. N. Reddy

Beilstein J. Org. Chem. 2009, 5, No. 14, doi:10.3762/bjoc.5.14

• ]. Its absolute stereochemistry was established by H. H. Meyer through stereoselective synthesis [25]. Recently Yadav et al. have synthesized (6R,2′S)-cryptocaryalactone and its epimer using stereoselective reduction of δ-hydroxy-β-keto ester [33]. All other possible isomers of cryptocaryalactone were

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

Analogues of amphibian alkaloids: total synthesis of (5R,8S,8aS)-(−)-8-methyl- 5-pentyloctahydroindolizine (8-epi-indolizidine 209B) and [(1S,4R,9aS)-(−)-4-pentyloctahydro- 2H-quinolizin- 1-yl]methanol

• Joseph P. Michael,
• Claudia Accone,
• Charles B. de Koning and
• Christiaan W. van der Westhuyzen

Beilstein J. Org. Chem. 2008, 4, No. 5, doi:10.1186/1860-5397-4-5

• hydroxymethyl substituent, is 38.8 ppm; whereas the corresponding chemical shift in epilupinine 13, the equatorial hydroxymethyl epimer, is 43.8 ppm [30]. The chemical shift difference of about 5 ppm between the C-1 equatorial and axial hydroxymethyl epimers appears to be general for quinolizidines [31]. A

Knorr- Rabe partial reduction of pyrroles: Application to the synthesis of indolizidine alkaloids

• Brendon S. Gourlay,
• John H. Ryan and
• Jason A. Smith

Beilstein J. Org. Chem. 2008, 4, No. 3, doi:10.1186/1860-5397-4-3

• of the proposed structure of indolizidine 167B by the catalytic hydrogenation of (−)-24 (Scheme 8) [17], and herein we report the racemic synthesis of its epimer (Scheme 9). We have reported the synthesis of the bicyclic ketone (±)-24 [18] and subjection of this α-ketopyrrole to the modified Knorr

A divergent asymmetric approach to aza-spiropyran derivative and (1S,8aR)-1-hydroxyindolizidine

• Jian-Feng Zheng,
• Wen Chen,
• Su-Yu Huang,
• Jian-Liang Ye and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2007, 3, No. 41, doi:10.1186/1860-5397-3-41

• quantitative yield. The result means that a tandem dehydration-THP cleavage-intramolecular nucleophilic addition occurred. When the stirring was prolonged to 2 h, about 5% of another epimer (no shown) was also formed according to the 1H NMR analysis. The stereochemistry of the aza-spiropyran 7 was determined

• . [36][37][38] The trans-diastereomer reacts much more slower than the cis-diastereomer, and some un-reacted trans-epimer was always recovered even starting with a pure cis-diastereomer. In the present study, not only both two diastereomers have been completely converted to the aza-spiropyran 7, what is

The enantiospecific synthesis of (+)-monomorine I using a 5-endo- trig cyclisation strategy

• Malcolm B. Berry,
• Donald Craig,
• Philip S. Jones and
• Gareth J. Rowlands

Beilstein J. Org. Chem. 2007, 3, No. 39, doi:10.1186/1860-5397-3-39

• epimer, with the methyl group residing in the axial position. Naturally, we had assumed that the diastereoisomer in which all the substituents adopted a pseudo-equatorial orientation would have been formed preferentially. Yet inspection of the possible transition states for the cyclisation 25 vs. 27

Flexible synthesis of poison- frog alkaloids of the 5,8-disubstituted indolizidine- class. II: Synthesis of (-)-209B, (-)-231C, (-)-233D, (-)-235B", (-)-221I, and an epimer of 193E and pharmacological effects at neuronal nicotinic acetylcholine receptors

• Soushi Kobayashi,
• Naoki Toyooka,
• Dejun Zhou,
• Hiroshi Tsuneki,
• Tsutomu Wada,
• Toshiyasu Sasaoka,
• Hideki Sakai,
• Hideo Nemoto,
• H. Martin Garraffo,
• Thomas F. Spande and
• John W. Daly

Beilstein J. Org. Chem. 2007, 3, No. 30, doi:10.1186/1860-5397-3-30

• antagonist for this receptor, dihydro-β-erythroidine. Results The enantioselective syntheses of (-)-209B, (-)-231C, (-)-233D, (-)-235B", (-)-221I, and what proved to be an epimer of natural 193E, starting from common chiral lactams have been achieved. When we performed electrophysiological recordings to

• epimer of 193E starting from common chiral lactams, and the absolute stereochemistry of natural (-)-233D was determined. Furthermore, the relative stereochemistry of (-)-231C and (-)-221I was also determined. The present asymmetric synthesis of the proposed structure for 193E revealed that the C-8

• , and an alkaloid that proved to be an epimer of natural indolizidine 193E. The alkaloids (-)-209B and (-)-235B" are known to be noncompetitive nicotinic blockers [2], but effects of the other compounds have not yet been tested. To explore possible subtype selectivity, we examined the effects of

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

• previously proposed indirect mechanism. Consistent with the general trend in related compounds, the title compound showed lower affinity at the kappa opioid receptor than the natural epimer salvinorin B (2a). The related 8-epi-acid 4b showed no affinity. Introduction Salvinorin A (1a), isolated from the

• ) itself, whose binding affinity (Ki = 43 nM) was reportedly greater than that of the natural epimer 2a (111 nM).[8] To explore this anomaly, we submitted a new sample of 2b for in vitro testing at the KOR. Binding affinity, potency and efficacy were determined as previously described (Table 1).[26] The

• ), but the 8-epimer 4b showed high affinity at the KOR (49 nM).[23] In contrast, our current samples of both 4a and 4b showed no affinity at the KOR (Table 1). Given the very high binding affinity of 1a, contamination of an inactive or weakly active compound with even traces of 1a will cause large errors

Methods for the synthesis of polyhydroxylated piperidines by diastereoselective dihydroxylation: Exploitation in the two-directional synthesis of aza-C-linked disaccharide derivatives

• Andrew Kennedy,
• Adam Nelson and
• Alexis Perry

Beilstein J. Org. Chem. 2005, 1, No. 2, doi:10.1186/1860-5397-1-2

• ] neither face of the alkene is hindered by two allylic substituents, and low diastereoselectivity was observed (see Figure 3). Remarkably, the pentaacetate 22D was obtained as a single side chain epimer. Determination of the configuration of the dihydroxylation products The relative configurations and