First stereoselective total synthesis of decytospolides A and B

The first stereoselective total synthesis of decytospolides A and B has been accomplished starting from n-hexanal. The key steps involved in this synthesis are Horner-Wittig reaction, Sharpless asymmetric epoxidation, and oxa-Michael reaction.     

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.     

Synthesis, photophysical properties, and cyanide detection in aqueous solution of BF2-curcumin dyes

Derivatives of difluoroboron curcumin (BF₂-curcumin, BF₂-cur(OMe)₂, BF₂-cur(OTs)₂, and BF₂-curOTs), were synthesized. All compounds possessed electron donor moieties at both ends of the conjugated π system and an electron acceptor moiety in the middle of the molecules (D-A-D system) and should exhibit different optical properties depending on substituents on the benzene rings. Photophysical properties of curcumin and difluoroboron curcumin derivatives were explored. The electron-withdrawing substituent could decrease the electron acceptability of BF₂-acceptor moiety resulting in the hypsochromic shift of both absorption and emission bands. BF₂-curcumin and BF₂-cur(OMe)₂ displayed the positive solvatochromic effect relying predominantly on polarity and polarizability of the solvent. Interestingly, BF₂-curcumin showed high selectivity and sensitivity towards cyanide with the detection limits of 22 μM and 0.14 μM measured by visual detection and UV-vis spectrophotometry, respectively. Compared to the original curcumin, BF₂-curcumin offered a remarkably promising detection of cyanide with 66-fold enhancement in aqueous media (4:1 of CH₃CN/H₂O).     

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.     

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.     

Polyhalogenoheterocyclic compounds: Part 54: [1] Suzuki reactions of 2,4,6-tribromo-3,5-difluoropyridine

Palladium catalysed Suzuki cross-coupling reactions between 2,4,6-tribromo-3,5-difluoropyridine and a short series of aromatic boronic acid derivatives gave 4-bromo-3,5-difluoro-2,6-diphenylpyridine derivatives arising from displacement of bromine atoms attached to positions ortho to ring nitrogen or the corresponding triaryl systems depending on the reaction conditions. Consequently, the use of polybromofluoropyridine scaffolds for the synthesis of polyfunctional heteroaromatic derivatives is expanded further.     

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.     

A highly efficient synthesis of 22-deoxy-OSW-1 by utilizing the intact skeleton of diosgenin

22-Deoxy-OSW-1 (1), an analogue of OSW-1 with the potent anticancer activity, was synthesized by utilizing the intact skeleton of diosgenin in 11 steps in 13.7% overall yield. This synthesis demonstrated an effective and reasonable synthetic strategy for bioactive steroids with side chains.     

Bis(3-pyridyl)methylvinylsilane (L1) and 1,2-di(3-quinolyl) dimethyl disilane (L2): Synthesis and complexation reactions. Anion controlled solid state structures of cationic Ag(I)-L1 complex

3-Bromopyridine and 3-bromoquinoline on reaction with n-butyllithium give lithiated products which on reaction with dichloromethylvinylsilane and 1,2-dichlorodimethyldisilane at −78 °C result in the ligands bis(3-pyridyl)methylvinylsilane (L1) and 1,2-di(3-quinolyl)dimethyl disilane (L2). The complexation reactions of both these ligands with Ag(I), Pd(II) and Cu(II) have been explored. The ¹H, ¹³C{¹H} and ²⁹Si{¹H}NMR and IR spectra of both the ligands and their metal complexes have been found characteristic. The complex of L1 with silver(I), [Ag(L1)]ClO₄ (1) gives suitable single crystals characterized by X-ray diffraction. Its structure consists of two dimensional sheets, having 25-membered metallamacrocycle ring, in which Ag has distorted tetrahedral geometry and is bonded to vinyl (η²) group. On reacting AgCF₃SO₃ with L1 and subjecting the single crystals of the resulting complex to X-ray diffraction it has been found that contrary to 1 there is no bond between vinyl group and silver, resulting in infinite molecular strands, in which coordination geometry of silver is distorted trigonal planar. anion acts as a bridge between two molecular strands through F?H (aromatic) and Ag?O secondary interactions. The Ag-C distances in 1 are 2.309(5) and 2.350(12) Å. The CC bond length does not exhibit significant change on bonding with silver in 1.     

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.     

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.     

Spin chemistry of organometallic compounds 5. Interaction of N-bromohexamethyl disilazane with substituted silyl hydrides

Reaction of N-bromohexamethyl disilazane (Me₃Si)₂NBr with substituted triorganyl silanes R¹R²R³SiH results in asymmetric disilazanes Me₃SiNHSiR¹R²R³ and bromination product, bromotrimethyl silane Me₃SiBr. The reaction has demonstrated an unusual dependence on specific solvation. In benzene, bromination occurs immediately after mixing of the reagents, while in cyclohexane, the reaction products are formed only under UV-irradiation. Application of photoinduced CIDNP method has shown that the mechanism of bromination of triorganyl silanes is comprised of a series of consecutive radical stages involving N-centered disilazanyl (Me₃Si)₂N and Si-centered silyl R¹R²R³Si radicals.     

Synthesis of 3-iodothiophenes via iodocyclization of (Z)-thiobutenynes

A simple synthesis of 3-iodothiophenes was demonstrated using a wide range of (Z)-thioenynes. The key step in the iodocyclofunctionalization was the selective reduction of the triple bond in (Z)-thioenynes by the addition of iodine as an electrophilic agent. The 3-iodothiophenes were obtained in good to excellent yields of 61–92%. The 3-iodothiophenes were used as substrates in Sonogashira cross-coupling reactions to obtain thiophene acetylenes.     

Synthetic studies on (−)-FR182877: construction of the ABCD ring system via the intramolecular cycloadditions (2)

Construction of the ABCD ring system of (−)-FR182877 via the intramolecular Diels-Alder (IMDA) reaction and the highly diastereoselective intramolecular hetero-Diels-Alder (IMHDA) reaction is described. The IMHDA reactions of the substrates incorporating the oxabutadiene with the E- or Z-alkene were examined, revealing that the sole product was obtained from both substrates and the E-alkene geometry was found to be crucial to obtaining the desired product.     

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.     

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 1-indanones by intramolecular Friedel-Crafts reaction of 3-arylpropionic acids catalyzed by Tb(OTf)3

Intramolecular Friedel-Crafts acylation reaction of 3-arylpropionic acids was efficiently catalyzed by Tb(OTf)₃ at 250 °C to give 1-indanones. Even deactivated 3-arylpropionic acids with halogen atoms on the aromatic ring can be cyclized in moderation to good yields.     

(p-Sulfomethyl)phenylalanine as a mimic of O-sulfatyl-tyrosine in synthetic partial sequences of P-Selectin glycoprotein ligand 1 (PSGL-1)

Fmoc-l-(p-sulfomethyl)phenylalanine, a bioisosteric mimic of acid-sensitive O-sulfatyl tyrosine, was synthesized from l-tyrosine according to a novel route. Partial sequences of the recognition site of P-Selectin glycoprotein ligand 1 (PSGL-1), which contain (sulfomethyl)phenylalanine were synthesized on solid-phase. By fragment condensation, a sialyl Lewis^x peptide conjugate containing a (sulfomethyl)phenylalanine mimic of O-sulfatyl tyrosine was prepared without destruction of the acid-sensitive fucoside bond within the saccharide side chain. Compounds of this type are of interest as sufficiently acid-stable potential inhibitors of P-Selectin in inflammatory processes.     

Study on fluorescent switching of naphthopyran with carbazole and pyrene dyad immobilized on SBA-15

A naphthopyran-bridge-carbazole dyad (CzNP), which exhibits both fluorescence and photochromism was synthesized. Then the CzNP was grafted into SBA-15-NH₂, with particular focus on how the SBA-15-NH₂ affects the photoswitching fluorescence change properties. A double fluorescence photochromic material, which was prepared by reacting 1-Pyrenecardboxaldehyde(PY-CHO):naphthopyran-carbazole(CzNP)=1:1 (molar ratio) with SBA-15-NH₂ was also synthesized. Naphthopyran in this two systems displayed excellent photochromic performance. The fluorescent emission was modulated between ‘on’ and ‘off’ via the photoisomerization of naphthopyran in high-degree, especially in PY-CzNP-SBA-15-NH₂ (>90%) due to the photoinduced energy transfer from pyrene excimers to the opened-form naphthopyran and the photoinduced electron transfer between carbazoles and the opened-form naphthopyran moiety. Both the fluorescence photoswitching CzNP-SBA-15-NH₂ and PY-CzNP-SBA-15-NH₂ in CH₃CN/H₂O (v/v, 1:1) solution displayed excellent fatigue resistance. The structural characteristics of CzNP-SBA-15-NH₂ and PY-CzNP-SBA-15-NH₂ were measured by FTIR spectra, X-ray diffraction (XRD), and Elemental analysis.     

Fluorometric sensing of Cu ion with smart fluorescence light-up probe, triazolylpyrene (Py)

We report the detection of Cu²⁺ ion with fluorescence light-up probe, triazolylpyrene (^TNDMBPy). Thus, the probe showed a remarkable fluorescence enhancement of both of the monomer and excimer emissions and a 2:1 probe-Cu²⁺ complexation with high selectivity, high stability constant and low detection limit. Formation of the excimer was also rationalized on the basis of DFT calculation. Our probe is also capable of sensing SDS micelle-encapsulated-Cu²⁺ ion in aqueous media with high association constant, thus, showing its practical utility. Thus, our probe could be used as an efficient Cu²⁺ ion selective fluorescence light-up probe, and may find applications in chemical and biological systems.