Synthesis of C18–C28 ketone fragment of micromonospolide B possessing 1,3-diene and 1,3-anti-diol functionalities

A highly stereocontrolled synthesis of the C18–C28 ketone fragment of the 16-membered plecomacrolide micromonospolide B has been accomplished. The C21–C23 syn–anti stereotriad is secured by the anti-selective aldol condensation of the ephedrine-derived chiral propionate with (E,E)-hexa-2,4-dienal and Sharpless asymmetric allylic epoxidation–regioselective reductive epoxide ring opening, respectively. The overall yield of this 14-step sequence is 18.4% and the target C18–C28 ketone was obtained in enantiomerically pure form.     

Total synthesis of emericellamides A and B

The total synthesis of emericellamides A and B is reported. A convergent, flexible strategy employing peptide chemistry, asymmetric alkylations, and culminating in macrolactamization is described. The previously reported structure of both compounds is confirmed.     

Stereoselective total synthesis of Ieodomycin A and B

The stereoselective total synthesis of Ieodomycin A and B, bioactive secondary metabolites from marine sources with potent anti-microbial activity was achieved starting from commercially available geranial. The key steps involved in the synthetic sequence of Ieodomycin A and B are the Sharpless asymmetric epoxidation, the formation of a β-ketoester, and the 1,3-anti reduction. The synthesis of C-3 epimer of Ieodomycin A and B was also accomplished in good yields.     

Total synthesis of attenols A and B

A concise approach for the total synthesis of attenols A and B is described involving MacMillan’s α-aminooxylation, Evan’s asymmetric alkylation, Brown’s allylation, and spiro-ketalization as key steps. This approach has successfully demonstrated the α-aminooxylation protocol for the construction of the anti-1,3-diol unit.     

Formal total synthesis of aspergillides A and B

The formal total synthesis of the cytotoxic 14-membered macrolides, aspergillides A and B is described. A combination of a chiron approach and an asymmetric synthesis is adopted for the synthesis of the target macrolides. The required 2,6-syn and 2,6-anti tetrahydropyrans were constructed via a tandem Sharpless asymmetric epoxidation and 6-exo cyclization on δ-hydroxy allylic alcohols, as the key steps. The requisite chiral synthon was prepared from l-ascorbic acid.     

A catalytic asymmetric anti-selective nitroaldol reaction with a neodymium-sodium heterobimetallic complex

A catalytic asymmetric anti-selective nitroaldol reaction with a neodymium-sodium heterobimetallic catalyst is described. A readily accessible amide ligand works efficiently as a chiral platform for the Nd/Na heterobimetallic catalyst in the reaction of various aldehydes and nitroethane, affording anti-1,2-nitro alkanols in good diastereo- and enantioselectivity.     

Nitrolaldol reaction of (R)-2,3-cyclohexylideneglyceraldehyde: a simple and stereoselective synthesis of the cytotoxic Pachastrissamine (Jaspine B)

(R)-2,3-Cyclohexylideneglyceraldehyde 1 has been found to be a good substrate for nitroaldol reaction both in anhydrous and aqueous conditions. In both cases, the reaction took place with good substrate-controlled anti-selectivity. The major nitroaldol product 2b has been exploited to develop a simple and stereoselective synthesis of jaspine B X. Also, beginning with nitroaldol reaction of 1, this route presents a simple approach for the stereoselective preparation of (anti–anti-5,7)- and (syn–syn-9, 11, 12)-1,2,3,4-alkanetetrols, each possessing three contiguous oxygenated stereocenters.     

Anti,anti acetals : Photoelectron spectroscopy of trans-1,8-dioxadecalins

The anti,anti acetals trans-1,8-dioxadecalin and trans-1,8-dioxa-4,5-dithiadecalin have been studied by photoelectron spectroscopy, and the electronic structure of the anti,anti acetal moiety was further elucidated by molecular orbital calculations on dimethoxymethane and visualized by stereoscopic drawings of the frontier orbitals.     

Preparation and application of 2-(arylmethoxy)isopinocampheols for the asymmetric aldol reaction of 3,3,3-trifluoropropionates

The preparation of 2-(arylmethoxy)isopinocampheols from pinanediol via the DIABL-H reduction of the corresponding aryl aldehyde acetals has been described. A systematic examination of the asymmetric aldol reaction of 3,3,3-trifluoropropionates led to the double diastereoselective aldol reaction of 2-(arylmethoxy)isopinocampheyl 3,3,3-trifluoropropionates providing anti-α-trifluoromethyl-β-hydroxy esters in 63-85% yields, ?99% anti-selectivity and 80-96% de for the anti-isomer.     

Quantitative analysis of 3‐OHB[a]P and (+)‐anti‐BPDE as biomarkers of B[a]P exposure in rats

The aim of this study was to develop an analytical method for the determination the levels of metabolites of benzo[a]pyrene (B[a]P), 3‐hydroxybenzo(a)pyrene (3‐OHB[a]P) and (+)‐anti‐benzo(a)pyrene diol‐epoxide [(+)‐anti‐BPDE, combined with DNA to form adducts], in rat blood and tissues exposed to B[a]P exposure by high‐performance liquid chromatography with fluorescence detection (HPLC/FD), and to investigate the usefulness of 3‐OHB[a]P and (+)‐anti‐BPDE as markers of intragastrical exposure to B[a]P in rats. The levels of 3‐OH‐B[a]P and B[a]P‐tetrol I‐1 released after acid hydrolysis of (+)‐anti‐BPDE in the samples were measured by HPLC/FD. The calibration curves were linear (r² > 0.9904), and the lower limit of quantification ranged from 0.34 to 0.45 ng/mL for 3‐OHB[a]P and from 0.43 to 0.58 ng/mL for (+)‐anti‐BPDE. The intra‐ and inter‐day stability assay data suggested that the method is accurate and precise. The recoveries of 3‐OHB[a]P and (+)‐anti‐BPDE were in the ranges of 73.6 ± 5.0 to 116.5 ± 6.3% and 73.3 ± 8.5 to 141.2 ± 13.8%, respectively. A positive correlation was found between the concentration of intragastrical B[a]P and the concentrations of 3‐OH‐B[a]P and (+)‐anti‐BPDE in the blood and in most of the tissues studied, except for the brain and kidney, which showed no correlation between B[a]P and 3‐OHB[a]P and between B[a]P and (+)‐anti‐BPDE, respectively. A sensitive, reliable and rapid HPLC/FD was developed and validated for analysis of 3‐OHB[a]P and (+)‐anti‐BPDE in rat blood and tissues. There was a positive correlation between the concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the blood and the concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the most other tissues examined. The concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the blood could be used as an indicator of the concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the other tissues in response to B[a]P exposure. These results demonstrate that 3‐OHB[a]P and (+)‐anti‐BPDE are potential biomarkers of B[a]P exposure, which would also be useful to assess the carcinogenic risks from B[a]P exposure. Copyright © 2015 John Wiley & Sons, Ltd.     

Theoretical investigation on the conformational space of perfluorohydroxylamine,F2NOF

The conformational space of perfluorohydroxylamine, F₂NOF, is studied using the CCSD/aug-cc-pVDZ level of theory. It is found that the lowest-energy form of F₂NOF exhibits an anti conformation. This finding agrees with other theoretical studies, which indicate that the anti form is the most stable conformation upon H₂NOH fluorination on oxygen and/or nitrogen takes place [L. Radom, W.J. Hehre, J.A. Pople, J. Am. Chem. Soc. 94 (1972) 2371]. On the other hand, the present result is in complete disagreement with recent theoretical studies, in which the syn form of F₂NOF is proposed to be the minimum-energy conformation [P. Antoniotti, F. Grandinetti, Chem. Phys. Lett. 366 (2002) 676]. An NBO analysis at the B3LYP/aug-cc-pVDZ level of theory reveals that the interaction between the nitrogen lone pair and the OF antibond on one hand, and interactions between one oxygen lone pair and the two NF antibonds on the other hand, are responsible for the deep minimum, in which the anti conformer lies. Only those stabilizing interactions originated in the abovementioned oxygen lone pair accounts for the very flat region, in which the syn form is located.     

Diastereo- and enantioselective synthesis of anti-1,3-mercapto alcohols from α,β-unsaturated ketones via tandem Michael addition–MPV reduction

A new and effective asymmetric synthesis of anti-1,3-mercapto alcohols 3 from α,β-unsaturated ketones 1 utilizing tandem Michael addition–Meerwein–Ponndorf–Verley (MPV) reduction is described. Transformation of the MPV products anti-4 via the Wagner–Meerwein rearrangement was optimized under acidic or basic conditions to afford 1,3-mercapto alcohols anti-3, depending on the substituent R² of 4.     

Selective hydrolysis of anti-1,3-diol-acetonides for the differentiation of 1,3-anti and 1,3-syn diols

A mild and general method for the selective cleavage of anti-1,3-acetonides has been developed for the differentiation of 1,3-anti and 1,3-syn diols in long chain polyolic fragments. The diluted acidic conditions applied to these systems are compatible with other common protecting groups such as silyl ethers and benzyloxymethyl ethers.     

Highly sensitive electrochemical immunoassay for human IgG using double-encoded magnetic redox-active nanoparticles

A new sandwich-type electrochemical immunoassay was developed for the detection of human IgG using doubly-encoded and magnetic redox-active nanoparticles as recognition elements on the surface of a glassy carbon electrode modified with anti-IgG on nanogold particles. The recognition elements were synthesized by coating magnetic Fe₃O₄ nanoparticles with Prussian blue nanoparticles and then covered with peroxidase-labeled anti-IgG antibodies (POx-anti-IgG) on Prussian blue nanoparticles. The immunoelectrode displays very good electrochemical properties towards detection of IgG via using double-encoded magnetic redox-active nanoparticles as trace and hydrogen peroxide as enzyme substrate. Its limit of detection (10 pmol·L^?1) is 10-fold better than that of using plain POx-anti-IgG secondary antibodies. The method was applied to the detection of IgG in serum samples, and an excellent correspondence with the reference values was found.     

A concise total synthesis of arizonins B1 and C1

A concise and efficient total synthesis of arizonins B1 and C1 is reported. A key building block alkyne is synthesized from d-glucono-δ-lactone and used in the Dötz benzannulation reaction to construct the naphthalene unit. An oxa-Pictet–Spengler reaction gave the pyran ring while an H₂SO₄ mediated isomerization set the correct stereochemistry of the target molecules. Alternatively, a direct anti-pyran stereochemistry was prepared in a TFA solvent. The synthesis is competitive to previous reports and marks the first enantioselective synthesis of arizonin B1.     

Stereoselective anti-SN2′ Mitsunobu reaction of α-hydroxy-α-alkenylsilanes

A novel silyl group-directed anti-S_N2′ reaction of allylic alcohols under Mitsunobu reaction conditions is described. The Mitsunobu reaction of α-hydroxy-α-alkenylsilanes with a TBS or TIPS group gave the anti-S_N2′ product, in which regio- and stereochemical outcomes of the reaction depended on the steric bulkiness of the silyl group.     

Reaction modes of oxidative dimerization of epoxycyclohexenols

Of the 16 possible modes of the oxidation-6π-electrocylization-Diels-Alder reaction cascade for an epoxyquinone, and eight for a 2-alkenyl-3-hydroxymethyl-2-cyclohexen-1-one, only the endo-anti(epoxide)-anti(Me)-hetero and endo-anti(Me)-hetero are respectively observed, while both the endo-anti(epoxide)-anti(Me)-hetero and exo-anti(epoxide)-anti(Me)-homo reaction modes occur with epoxy-4-hydroxycyclohexenones owing to a hydrogen-bonding interaction.     

Highly enantioselective synthesis of syn- and anti-propionate aldols without diastereoselection in the chiral oxazaborolidinone-promoted aldol reaction with a silyl ketene acetal derived from ethyl 2-(methylthio)propionate

A mixture of syn- and anti-aldol products containing an α-methylthio group were obtained in good yields with high enantioselectivities in the chiral oxazaborolidinone-promoted aldol reactions of a novel silyl ketene acetal, derived from ethyl 2-(methylthio)propionate, with aldehydes. Subsequent desulfurization resulted in an effective preparation of essentially enantiopure syn- and anti-propionate aldols which were separable.     

A new type of amino amide organocatalyzed enantioselective crossed aldol reaction of ketones with aromatic aldehydes

A new type of amino amide organocatalysts was designed and synthesized from commercially available amino acids in easy steps. Their catalytic activities were examined in enantioselective crossed aldol reaction of various acyclic and cyclic ketones with aromatic aldehydes to afford the corresponding chiral anti-aldol adducts with good to excellent chemical yields, diastereoselectivities and enantioselectivities (up to 99%, up to syn:anti?=?1:99, up to 97% ee).     

Internal rotation and framework relaxation in ethene thiol

New and existing data on the ground and excited CS torsional states of the stable rotamers of ethene thiol have been analysed to give a potential function for internal rotation around the CS bond. The barrier between the syn and anti rotamers is found to be 800 cm^?1 and that at the planar anti conformation itself to be 12 cm^?1. the syn conformation is 50 cm^?2 more stable than the ‘quasi-planar’ anti conformation Satisfactory reproduction of the observed trends in rotational constants with torsional excitations has been achieved by introducing extensive relaxation of the CCS angle and the CS bond length during internal rotation. The CCS angle reduces by up to 5° v'hilst the CS bond length increases by up to 0.02 A during rotation from the syn to anti conformation. The use of ab initio M.O. calculations to provide an indication of the most significant aspects of structure relaxation is described.