Tonkinensines A and B, two novel alkaloids from Sophora tonkinensis

Tonkinensines A (1) and B (2), two novel cytisine-type alkaloids that feature the skeleton with a linkage to pterocarpan, were isolated from the roots of Sophora tonkinensis. Their structures and absolute configurations were elucidated by spectroscopic methods, especially X-ray crystal diffraction and CD spectral analysis. The proposed biosynthetic pathway was also discussed. Both 1 and 2 were tested in HeLa and MDA-MB-231 tumor cell lines, and compound 2 showed moderate cytotoxic activity.     

First stereoselective total synthesis of trichodermone A

The first stereoselective total synthesis of trichodermone A using Baylis-Hillman and ring-closing metathesis (RCM) reactions as key steps is reported.     

Studies on the synthesis of phorboxazole B: stereoselective synthesis of the C28-C46 segment

A stereoselective synthesis of C28-C46 segment of phorboxazole B is described. Key features of the synthetic route involved the use of 1,3-asymmetric induction of Mukaiyama aldol reaction to construct the stereogenic center at C35, and the employment of metalated oxazole chemistry to prepare the ketal 6.     

Synthesis of the FG ring fragment of pectenotoxins 1-9

The synthesis of the FG ring fragment common to pectenotoxins 1-9 is reported. The successful, convergent synthesis relied on high yielding routes to access two key intermediates; aldehyde 1 and phosphonium salt 2. A Z-selective Wittig reaction gave access to advanced linear precursor 3, which was converted to FG ring fragment 4 using two sequential cyclization reactions.     

First stereoselective total synthesis of antibiotic macrolide Berkeleylactone F

The first stereoselective total synthesis of antibiotic macrolide Berkeleylactone F is described. The synthetic sequence notably features Sharpless kinetic resolution to access chiral epoxide followed by its regioselective ring-opening reaction, Sharpless asymmetric reaction and ring-closing metathesis.     

First stereoselective total synthesis of decytospolides A and B

The first synthesis of bioactive decytospolides A and B adopting an oxa-Michael addition as the key step is reported.     

First stereoselective total synthesis of seimatopolide A

The first stereoselective total synthesis of seimatopolide A (1) has been achieved. The key steps are Keck allylation, Sharpless asymmetric dihydroxylation, cross-, and ring-closing metathesis reactions.     

The first stereoselective and the total synthesis of Leiocarpin C and total synthesis of (+)-Goniodiol

The synthesis of the styryl lactone Leiocarpin C has been achieved in a highly stereoselective manner using Jacobsen’s kinetic resolution, Sharpless asymmetric epoxidation and Sharpless asymmetric dihydroxylation as key steps. This is the first total synthesis of Leiocarpin C, and thus establishes for the first time the absolute stereochemistry of this natural product.     

Disparate orientation of [1]rotaxanes

A novel [1]rotaxane 2 has been synthesized employing a 4-methyl-benzenesulfonyl and an azobenzene modified β-cyclodextrin (β-CyD) at the 2 position, through self-inclusion complexation and Suzuki-coupling capping in aqueous solution. Disparate absorption, induced circular dichroism (ICD) properties from its isomer [1]rotaxane 1, prepared from the isomeric β-CyD modifier at the 6 position, and the photoisomerization of [1]rotaxane 2 were thoroughly investigated.     

First stereoselective total synthesis of decarestrictine O via RCM protocol

A convergent first stereoselective total synthesis of decarestrictine O via RCM protocol starting from 1,3-propanediol and propylene oxide is reported.     

Enantiodivergent synthesis of the quinolizidine poison frog alkaloid 195C

Herein, we describe the enantiodivergent synthesis of the 1,4-cis-disubstituted quinolizidine alkaloid 195C. Although the stereoselectivity of the final hydrogenation reaction was low, we have proposed the first chiral total synthesis of both (−)- and (+)-195C as an enantiodivergent process.     

PS-SNAP, a practical polymer-supported nitrosation reagent in organic synthesis

PS-SNAP was designed and evaluated as a practical nitrosating polymer-supported reagent for the nitrosation of sec-amines. Nitrosated dialkyl amines, alkyl anilines, and bis-anilines were obtained in good yields and high purities after shaking the corresponding amines in the presence of an excess of the newly described reagent followed by simple filtration and removal of solvents.     

Five-membered heterocycles. Part III. Aromaticity of 1,3-imidazole in 5+n hetero-bicyclic molecules

The aromaticity (in the form of HOMA index) of 1,3-imidazole ring and its bicyclic derivatives was studied on the basis of statistical data from Cambridge Structural Database and X-ray investigations performed by authors. As a starting point, aromaticity of the 1,3-imidazoles with exocyclic X substituent at C2 (XN, O or S) was calculated. Subsequently, the HOMA index was calculated for various 5+n bicyclic skeletons with N, O, and S as endocyclic heteroatoms in the second ring. For the isolated 1,3-imidazole ring, aromaticity depends on exocyclic substituent at C2 and decreases in sequence N, S, O. For bicyclic derivatives it was found that both rings are aromatic and coplanar in very few molecules (17% of investigated ones), and positive charge—located on endocyclic heteroatom—increases the aromaticity. For remaining compounds, presence of sp³ carbons excludes possibility of aromatic ring existence.     

Efficient synthesis of trypsin inhibitor SFTI-1 via intramolecular ligation of peptide hydrazide

Cyclic peptide trypsin inhibitor SFTI-1 was synthesized via intramolecular ligation of a linear peptide hydrazide with high yield. This cyclization strategy did not cause epimerization at the C-terminal Arg residue. CD spectrum and NMR spectroscopy analysis demonstrated that well-folded SFTI-1 could be obtained via standard oxidative folding process. Thus, we present a simple and cost-efficient strategy for the synthesis of SFTI-1.     

A stereoselective CC free-radical cascade route to optically pure and potentially useful tetracyclic amines

Nucleophilic racemic amines have been synthesized utilizing a C⁷ⁿC^5x free-radical cascade reaction from a bis-allyl amine starting material. Being potentially useful organocatalytic bases as is evident from their screening in the Baylis-Hillman reaction, optically pure amines were also synthesized from optically pure aldehydes (−) or (+)-4. Bis-allyl amides under similar radical reaction condition resulted in C⁷ⁿ cyclized products.     

Facile organocatalytic domino oxidation of diols to lactones by in situ-generated TetMe-IBX

The domino oxidation of diols to lactones is an important transformation, and catalytic protocols that allow this conversion smoothly are scarce. Capitalizing on the established reactivity of tetramethyl-IBX (TetMe-IBX) and its in situ generation in the presence of a co-oxidant, such as oxone, we have shown that a variety of diols can be converted to the corresponding lactones in respectable yields by employing the precursor of TetMe-IBX, namely, tetramethyl-o-iodobenzoic acid (TetMe-IA), as a catalyst in 5 mol % in the presence of 2 equiv of oxone.     

Studies directed towards the stereoselective total synthesis of ilexlactone via a tandem ring-closing enyne metathesis protocol

Studies directed towards the stereoselective total synthesis of ilexlactone resulted in the synthesis of bicyclic systems 1a, 1b and ent-1a through tandem ring-closing enyne metathesis using Grubbs’ catalyst. The structures of synthetic 1a, 1b and ent-1a revealed that the proposed structure for ilexlactone is incorrect.     

A new simple route to deoxyamino sugars from non-sugar material: synthesis of d-tolyposamine and 4-epi-d-tolyposamine and formal synthesis of d-vicenisamine

A new, simple strategy has been formulated for the synthesis of deoxyamino sugars from a non-sugar starting material. Starting from the enantiomerically pure diol obtained from ethyl sorbate by Sharpless asymmetric dihydroxylation, the synthesis of two types of 2,3,4,6-tetradeoxy-4-amino sugars—d-tolyposamine and 4-epi-d-tolyposamine—, and formal synthesis of 2,4,6-trideoxy-4-amino sugar—d-vicenisamine—were performed.     

Stereoselective total synthesis of oplopandiol,oploxyne A,and oploxyne B

A stereoselective total synthesis of oplopandiol, oploxyne A, and (−)-oploxyne B is described. The key reactions include Sharpless asymmetric epoxidation, d-proline catalyzed aminoxylation, Cadiot–Chodkiewicz cross-coupling reaction, m-CPBA induced substrate-controlled stereoselective epoxidation, and Lewis acid catalyzed stereo- and regioselective ring-opening of epoxide.     

Stereoselective synthesis of trifluoromethylated vinyl- and dienylphosphonates with γ-alkoxycarbonyl moiety

Trifluoromethylated vinyl- and dienylphosphonates with γ-alkoxycarbonyl moiety have been synthesized via sequential transformations of bisphosphonates in 68-76% (three steps) yields with Z-isomers exclusively or predominantly.