Synthesis of porphyryl boronates with (un)saturated side-chains

Porphyrins with (un)saturated side-chains containing boron residues were developed as synthons for porphyrin functionalisation. Porphyrins with mono and bis-substituted unsaturated boronyl residues were prepared in good yields (52-66%) using a cross-metathesis approach in the presence of Grubbs I-generation catalysts. In all cases complete E-stereoselectivity (100%) was observed. Furthermore, formal cross-metathesis products with α,β-unsaturated chains smoothly underwent addition with bis(pinacolato)diboron [(Me₄C₂O₂)B-B(O₂C₂Me₄)] to yield the corresponding saturated boron compounds in 60-70% yields.     

Stereoselective Synthesis of Highly Functionalized Nitrocyclopropanes through the Organocatalyic Michael‐Addition‐Initiated Cyclization of Bromonitromethane and β,γ‐Unsaturated α‐Ketoesters

A highly diastereo‐ and enantioselective cyclopropanation of β,γ‐unsaturated α‐ketoesters with bromonitromethane has been successfully developed through a domino Michael‐addition/intramolecular‐alkylation strategy. Acceptable yields (up to 89 %) and enantioselectivities (up to 96 % ee) have been obtained.     

Organocatalyzed Cascade Aza‐Michael/Michael Addition for the Asymmetric Construction of Highly Functionalized Spiropyrazolone Tetrahydroquinolines

An organocatalyzed diastereo‐ and enantioselective cascade aza‐Michael/Michael addition of 2‐tosylaminoenones to unsaturated pyrazolones has been developed to afford novel chiral spiropyrazolone tetrahydroquinolines containing three contiguous stereocenters. This cascade reaction proceeded well with 2 mol % chiral bifunctional tertiary amine squaramide catalyst to give the desired products in excellent yields (up to 99 %) with excellent diastereoselectivity (up to >25:1 diastereomeric ratio) and high enantioselectivity (up to 91 % enantiomeric excess).     

Divergent synthesis of spirocyclopentene-pyrazolones and pyrano[2,3-c]-pyrazoles via Lewis base controlled annulation reactions

An effective Lewis base catalyst-controlled α-regioselective annulation reaction of γ-substituted allenoates with unsaturated pyrazolones has been developed, affording various spirocyclopentene-pyrazolones and pyrano[2,3-c]pyrazoles. The combination of PPh₃ and K₂CO₃ promoted the [3+2] annulation to access the spirocyclopentene-pyrazolones in moderate to good yields (up to 90%) with excellent diastereoselectivities (dr >19:1), while [4+2] annulations to generate pyrano[2,3-c]pyrazoles were successfully achieved by employing DBU as catalyst (in up to 92% yield). Of importance, the asymmetric synthesis of spirocyclopentene-pyrazolone was realized by using our previously reported chiral ferrocenylphosphine catalyst.     

Exploring the molecular basis for selective cytotoxicity of lamellarins against human hormone-dependent T47D and hormone-independent MDA-MB-231 breast cancer cells

Abstract  

The common structural requirements for cytotoxicity of lamellarins against two human breast cancer cell lines were determined using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) techniques. Twenty lamellarins were selected to serve as the training set, whereas another group of six compounds were used as the test set. The best CoMFA and CoMSIA models for both cell lines yielded satisfactory predictive ability with r _cv² values in the range of 0.659–0.728. Additionally, the contour maps obtained from both the CoMFA and CoMSIA models agreed well with the experimental results and may be used in the design of more potent cytotoxic compounds for human breast cancers. Both analyses not only suggested structural requirements of various substituents around the lamellarin skeleton for their cytotoxic activity against both human breast cancer cell lines but also revealed the molecular basis for the differences between the saturated and unsaturated D-rings of the lamellarins.     

New 1,3-dipolar cycloaddition/dehydrogenation of azomethines ylides and azodicarboxylates: direct and effective construction of unsaturated 1,2,4-triazolines

The first K₂CO₃-catalyzed 1,3-dipolar cycloaddition/dehydrogenation of azodicarboxylates with azomethines was developed and a wide range of unsaturated 1,2,4-triazolines have been successfully prepared in good yields (up to 93%).     

Improved preparation and characterization of unsaturated γ-lactones

Improved, high yield procedures for the preparation of unsaturated γ-lactones (I-IV) from saturated γ-lactones (V) are described. Compounds V are first converted to the sodium salts of the corresponding γ-hydroxy acids (VI) (100%) which are oxidized within fifteen minutes to the γ-keto acids (VII) (75–85%) by bromine at pH 6-7.5. Acid-catalyzed reaction of VII with acetic anhydride at room temperature for fifteen minutes yields γ-acetoxy-γ-lactones (VIII) (70–90%). Pyrolysis of VIII at 200–330° yields I-IV (70–95%), the composition of which depends on whether strongly acidic contaminants have been completely removed from VIII prior to pyrolysis. In selected cases studied, fractional distillation permits the isolation of pure unsaturated lactones. Nmr has been extensively used to determine purity at each step and the composition of mixtures of I-IV.     

Enantioselective synthesis of chiral sulfones by ir-catalyzed asymmetric hydrogenation: a facile approach to the preparation of chiral allylic and homoallylic compounds

A highly efficient and enantioselective Ir-catalyzed hydrogenation of unsaturated sulfones was developed. Chiral cyclic and acyclic sulfones were produced in excellent enantioselectivities (up to 98% ee). Coupled with the Ramberg-B?cklund rearrangement, this reaction offers a novel route to chiral allylic and homoallylic compounds in excellent enantioselectivities (up to 97% ee) and high yields (up to 94%).     

InCl3 catalyzed carbene insertion into O-H bonds: efficient synthesis of ethers

An efficient InCl₃ mediated insertion of the carbene fragment (:CHCO₂Et), generated in situ from ethyl diazoacetate into O-H bond of a series of saturated and unsaturated alcohols under mild conditions has been developed to afford the corresponding ethers as exclusive products in good to high yields (70-95%) and in shorter reaction times. In the case of unsaturated alcohols, the reaction proceeded with unprecedented selectivity resulting in ethers as the only products and in high yields.     

Total synthesis of (-)-leuconicine A and B

Concise asymmetric total syntheses of Strychnos alkaloids (-)-leuconicine A (14 steps, 9% overall yield) and B (13 steps, 10% overall yield) have been accomplished. Key steps include (1) our sequential one-pot spiro-cyclization/intramolecular aza-Baylis-Hillman method to prepare the ABCE framework; (2) a novel domino acylation/Knoevenagel cyclization to prepare the F-ring; and (3) a Heck cyclization to access the D-ring.     

Electrogenerated N-heterocyclic carbenes: N-functionalization of benzoxazolones

A simple electrochemical procedure for the N-acylation and N-alkylation of benzoxazol-2(3H)-ones has been set up via electrolysis of an ionic liquid containing a benzoxazolone followed by addition of saturated or unsaturated anhydrides or alkyl halides. The electrochemically induced N-functionalization of benzoxazol-2(3H)-ones works very well in all tested ionic liquids, avoiding the use of volatile organic solvents. The N-acyl and N-alkyl derivatives of benzoxazol-2(3H)-ones were isolated in good to excellent yields; moreover, the ionic liquid has been reused fivefold maintaining the high yield of the products.     

Rhodium‐Catalyzed Regioselective C7‐Functionalization of N‐Pivaloylindoles

An efficient rhodium‐catalyzed method for direct C? H functionalization at the C7 position of a wide range of indoles has been developed. Good to excellent yields of alkenylation products were observed with acrylates, styrenes, and vinyl phenyl sulfones, whereas the saturated alkylation products were obtained in good yield with α,β‐unsaturated ketones. Both the N‐pivaloyl directing group and the rhodium catalyst proved to be crucial for high regioselectivity and conversion.     

Markovnikov‐Selective Palladium Catalyst for Carbonylation of Alkynes with Heteroarenes

A new class of palladium catalysts, based on heterocyclic diphosphines, was rationally designed and synthesized. Application of one of these catalysts allows novel Markovnikov‐selective carbonylation of non‐activated alkynes with heteroarenes to give the corresponding branched α,β‐unsaturated ketones in excellent yields (up to 97 %) and regioselectivities (b/l up to 99:1). In addition to heteroarenes, other common nucloephiles (alcohol, phenol, amine, and amide) furnish the desired carbonylation products smoothly in high yields.     

Studies in chlorin chemistry. 3. A practical synthesis of c,d-ring symmetric chlorins of potential utility in photodynamic therapy

[reaction: see text] C,D-ring symmetric chlorins 8 were prepared in 47-85% yield, on scales up to several hundred milligrams, by condensation of appropriately substituted bis-formyldihydrodipyrrins 6 and dipyrromethane bis-carboxylic acids 7 in 5% TFA/CH2Cl2 (25 examples). Target chlorins were chosen to systematically probe the effect of lipophilic and hydrophilic substituents on tissue partitioning and cellular membrane penetration in photodynamic therapy (PDT).     

The reactivity of 2,2"-bipyridine complexes in the electrochemical reduction of organohalides

Nickel(0) complexes coordinatively unsaturated with 2,2"-bipyridine (bpy) are more reactive in the oxidative addition to organic halides than the saturated analogs. -Organonickel complexes formed as intermediates of catalytic cycles were prepared in high yields using nickel complexes coordinatively unsaturated with bpy and aromatic halides containing a methyl group in the ortho-position of the ring.     

Profiling the metabolic difference of seven tanshinones using high-performance liquid chromatography/multi-stage mass spectrometry with data-dependent acquisition

Tanshinones are a class of bioactive constituents in the roots of Salvia miltiorrhiza named Dan-Shen in Chinese, which possess diverse pharmacological activities. In this study, we employed a sensitive high-performance liquid chromatography/multi-stage mass spectrometry (HPLC/MS(n)) method with data-dependent acquisition and a dynamic exclusion program for the identification of phase I metabolites of seven tanshinones in rat bile after intravenous administration. These seven tanshinones are tanshinone IIA, sodium tanshinone IIA sulfonate (abbreviated as STS, a water-soluble derivate of tanshinone IIA), cryptotanshinone, 15,16-dihydrotanshinone I, tanshinone IIB, przewaquinone A and tanshinone I. Altogether 33 metabolites underwent monohydroxylation, dihydroxylation, dehydrogenation, D-ring hydrolysis or oxidation reactions in the C-4 or C-15 side chain which were characterized by analyzing the LC/MS(n) data. Different metabolic reactions for tanshinones were dependent on the degree of saturation and the substituent group in the skeleton. Dehydrogenation was the major metabolic modification for cryptotanshinone with saturated A and D rings. 15,16-Dihydrotanshinone I containing a saturated D ring was mainly metabolized through D-ring hydrolysis. For tanshinone IIA, possessing a saturated A ring, hydroxylation was the major metabolic pathway. When there was hydroxyl group substitution in the C-17 or C-18 position, such as przewaquinone A and tanshinone IIB, or sulfonic group substitution in the C-16 position, such as STS, higher metabolic stability than that of tanshinone IIA was shown and only trace metabolites were generated. Oxidation in the C-4 or C-15 side chain was a characteristic reaction for tanshinone IIA and hydroxylated tanshinone IIA. For tanshinone I, bearing unsaturated A and D rings simultaneously, no metabolites were detected.     

One-pot sequences of reactions with sol-gel entrapped opposing reagents: an enzyme and metal-complex catalysts

We extend our sol-gel methodology of one-pot sequences of reactions with opposing reagents to an enzyme/metal-complex pair. Sol-gel entrapped lipase and sol-gel entrapped RhCl[P(C(6)H(5))(3)](3) or Rh(2)Co(2)(CO)(12) were used for one-pot esterification and C-C double bond hydrogenation reactions, leading to saturated esters in good yields. When only the enzyme is entrapped, the homogeneous catalysts quench its activity and poison it. Thus, when 10-undecenoic acid and 1-pentanol were subjected in one pot to the entrapped lipase and to homogeneously dissolved RhCl[P(C(6)H(5))(3)](3) under hydrogen pressure, only 7% of the saturated 1-pentyl undecanoate was obtained. The yield jumped 6.5-fold when both the enzyme and the catalyst were immobilized separately in silica sol-gel matrixes. Similar one-pot esterifications and hydrogenations by sol-gel entrapped lipase and heterogenized rhodium complexes were carried out successfully with the saturated nonoic, undecanoic, and lauric acids together with several saturated and unsaturated alcohols. The use of (S)-(-)-2-methylbutanol afforded an optically pure ester. The heterogenized lipase is capable of inducing asymmetry during esterification with a prochiral alcohol. Both the entrapped lipase and the immobilized rhodium catalysts can be recovered simply by filtration and recycled in further runs without loss of catalytic activity.     

Donor–acceptor complexes in copolymerization. LVIII. Alternating diene–dienophile copolymers. 12. Structure of furan–maleic anhydride copolymers prepared from the monomers and the diels-Alder adduct

The copolymerization of furan with maleic anhydride in the presence of a perester or azobisiso-butyronitrile at 50 or 70°C yields an unsaturated equimolar, alternating copolymer in which the furan units have 3,4 unsaturation and 2,5 linkages. The furan–maleic anhydride Diels-Alder adduct undergoes retrograde dissociation in solution at 70°C and, in the presence of radical catalysts, yields the same unsaturated alternating copolymer as is obtained from the monomers. The adduct undergoes homopolymerization in the presence of a rapidly decomposing perester at 50°C to yield a saturated polymer having a rearranged structure containing 3-oxabicyclo[2.2.1]heptane-5,6-dicarboxylic anhydride repeating units with 2,7 linkages.     

Enantioselective Copper(I/II)‐Catalyzed Conjugate Addition of Nitro Esters to β,γ‐Unsaturated α‐Ketoesters

A highly enantioselective Michael addition of nitroacetates to β,γ‐unsaturated α‐ketoesters was developed by using chiral copper catalysts. The Michael addition products can be obtained in high yields with up to 99 % ee. With these densely functionalized products, the chiral cyclic nitrones, which are important synthetic intermediates, can be obtained in one step.     

Asymmetric Desymmetrization of Saturated and Unsaturated meso-1,2-Diols

An asymmetric desymmetrization of saturated and unsaturated cyclic and acyclic meso-1,2-diols has been developed from the ene acetals, prepared from the norbornene carboxyaldehyde and meso-1,2-diols. The intramolecular haloetherification of the ene acetals as a key step afforded 8-membered acetals in a stereoselective manner just by the reaction of norbornene olefin even when the ene acetals from unsaturated meso-1,2-diols having olefins in the same molecule were used. Subsequent reductive elimination, followed by protecting the hydroxy group and transacetalization, gave optically active 1,2-diol derivatives and the starting ene acetals in good yields.