Ketal Function Research Articles

Synthesis of novel L-lactic acid-based plasticizers and their effects on the flexibility, crystallinity, and optical transparency of poly(lactic acid)

Using bio-based plasticizers derived from biomass resources to replace traditional phthalates can avoid the biotoxicity and non-biodegradability caused by the migration of plasticizers during the application of plastics. In this study, L-lactic acid and levulinic acid were employed as the major biomass monomer to successfully fabricate L-lactic acid-based plasticizers (LBL-n, n = 1.0, 1.5, 2.0, 2.5) containing a diverse number of lactate groups. The plasticizing mechanism was explained, manifesting that L-lactic acid-based plasticizers containing a substantial number of lactate groups could effectively improve the flexibility of poly (lactic acid) (PLA), and the elongation at break was 590 %–750 %. Compared to LBL-1.5 plasticized-PLA films, the tensile strength and modulus of ketonized-LBL-1.5 (KLBL-1.5) plasticized-PLA films increased to 59 % and 163 %, indicating the ketal functionality of plasticizers enhanced the strength of PLA. Meanwhile, the increment of lactate groups and the introduction of the ketal group in the plasticizer increased the crystallization, migration, and volatilization stability of plasticized-PLA films and also kept their outstanding optical transparency. Besides, the biodegradability of KLBL-1.5 was investigated by active soil and Tenebrio molitor experiments, and its degradation products were characterized. The findings indicated that KLBL-1.5 was fully decomposed. Taken together, this paper offers new promise for developing high-efficiency and biodegradable plasticizers.

Cytotoxicity of novel cross-conjugated arylated cyclopentene-1,3-diones

Novel 2,4-dichloro-5-phenylcyclopent-4-ene-1,3-dione and 5-aryl-4-chlorocyclopent-4-ene-1,3-dione were synthesized by the Suzuki–Miyaura or Friedel–Crafts reactions of the di- and trichlorocyclopentenone monoketals and subsequent hydrolysis of the ketal function. Condensation of these diones with (hetero)aromatic aldehydes afforded multifunctional 1,3-cyclopentenediones that showed anticancer activity.Keywords: organochlorine compounds, cyclopentenones, ketals, Suzuki–Miyaura reaction, Friedel–Crafts reaction, Knoevenagel condensation, aldehydes, cross-conjugated cyclopentene-1,3-diones, cytotoxicity.

Quantification of photooxidative defects in weathered microplastics using 13C multiCP NMR spectroscopy.

Weathering of microplastics made of commodity plastics like polystyrene, polypropylene and polyethylene introduces polar polymer defects as a result of photooxidation and mechanical stress. Thus, hydrophobic microplastic particles gradually become hydrophilic, consisting of polar oligomers with a significant amount of oxygen-bearing functional groups. This turnover continuously changes interactions between microplastics and natural colloidal matter. To be able to develop a better understanding of this complex weathering process, quantification of the corresponding defect proportions is a first and essential step. Using polystyrene, 13C enriched at the α position to 23%, we demonstrate that 13C cross polarisation (CP) NMR spectroscopy allows for probing the typical alcohol, peroxo, keto and carboxyl defects. Even the discrimination between in- and end-chain ketones, carboxylic acids and esters as well as ketal functions was possible. Combined with multiCP excitation, defect proportions could be determined with excellent accuracy down to 0.1%. For materials with 13C in natural abundance, this accounts for a detection limit of roughly 1%. The best trade-off between measurement time and accuracy for the quantification of the defect intensities for multiCP excitation was obtained for CP block lengths shorter than 250 μs and total build-up times longer than 2 ms. Further measurement time reduction is possible by using multiCP excitation to calibrate intensities obtained from series of 13C CP MAS NMR spectra. As photooxidation is an important degradation mechanism for microplastics in the environment, we expect these parameters to be transferable for probing defect proportions of weathered microplastics in general.

Xylariaopyrones E–I, five new α-pyrone derivatives from the endophytic fungus Xylariales sp. (HM-1)

Five new α-pyrones, xylariaopyrones E–I (1–5), along with three known analogues (6–8) were isolated from the cultivation broth of the endophytic fungus Xylariales sp. (HM-1). The structures of the new compounds including their absolute configurations were elucidated by comprehensive spectroscopic methods and quantum ECD calculations. Xylariaopyrone E (1) is the first example of α-pyrone derivative with a novel [3, 2, 0] bridge ring system via a ketal function group in the side chain. In bioactivity assays, xylariaopyrones E–G (1–3) showed moderate inhibiting activities against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa with MIC values from 25.4 to 64.5 μg/mL, whereras xylariaopyrone G (3) exhibited significant inhibition of monoamine oxidase B with an IC50 value of 15.6 μmol/L. Xylariaopyrone H (4) and the known compound 7 showed moderate toxicity against brine shrimp larvae with inhibition rates of 42.8% and 44.5%, respectively.

Synthesis of oligo(spiroketal)s by polycondensation of silyl ethers derived from naturally occurring myo‐inositol with 1,4‐cyclohexanedione

ABSTRACTOligo(spiroketal)s (OSKs) were synthesized from myo‐inositol, a naturally occurring cyclic compound bearing six hydroxyl groups. The successful synthesis of OSKs was achieved using silyl ethers 2 derived from 1,4‐di‐O‐alkylated myo‐inositol 1 as monomers, which underwent polycondensation with 1,4‐cyclohexanedione (CHD) at 0 °C in the presence of trimethylsilyl triflate as a catalyst. Because of the irreversible nature of the condensation reaction of silyl ethers with ketones, the resulting OSKs 7 had higher molecular weights than previously reported OSKs that were obtained by polycondensation of tetraols 1 with CHD, where backward hydrolysis of the ketal functions occurred. In addition, another series of OSKs, 8, were synthesized using silyl ethers 3 derived from 2,5‐di‐O‐alkylated myo‐inositol 6, which are more symmetric monomers than silyl ethers 2. Silyl ethers 3 underwent efficient polycondensation with CHD, whereas tetraol 6 did not, demonstrating that the derivation of such tetraols into the corresponding silyl ethers is a powerful strategy to access OSKs. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2407–2414

Xylariaopyrones A-D, four new antimicrobial α-pyrone derivatives from endophytic fungus Xylariales sp

Four new α-pyrone derivatives, xylariaopyrones A-D (1-4), together with four known compounds were isolated from the PDB broth of endophytic fungus xylariales sp. (HM-1). Their structures were identified by comprehensive analysis of NMR, MS and CD spectra. The absolute configurations of compounds B-D were determined by calculating their ECD spectra. Compound C (3) and D (4) was a pair of epimer with a ketal function group. The eight obtained metabolites were evaluated to four cancer cell lines, but they showed no significative data with IC50 > 50 μg/mL. And the antimicrobial assay results appeared that xylariaopyrones A-D displayed the inhibiting activity with MIC value ranging from 20.5 to 50.6 μg/mL. Finally, the results of brine shrimp inhibiting activity from eight compounds displayed different inhibiting ratio from 40% to 92%.

Rigid Polyurethanes, Polyesters, and Polycarbonates from Renewable Ketal Monomers

Two novel biobased diols containing rigid cyclic ketal functionalities have been synthesized on a relatively large scale from glycerol and two diketones, i.e., 1,4-cyclohexanedione and 4,4′-bicyclohexanone. The diols have been used in several types of step growth reactions, resulting in polycarbonates, polyesters, and polyurethanes. While molecular weights (Mn) of up to 50 kg mol–1 are obtained for the polyurethanes, they also exhibit high glass transition (Tg = 95–150 °C) and degradation temperatures (Td = 260–320 °C), are transparent, and show a high mechanical strength (E = 1.10–1.35 GPa) but brittle behavior. For the polycarbonates, Mn values higher than 24 kg mol–1 and Tg’s in the range of 70–100 °C have been obtained. Moreover, the polycarbonates show good mechanical properties like ductility and are transparent. Finally, a new generation of fully renewable polyesters have been synthesized with dimethyl succinate and dimethyl furan dicarboxylate. While moderate molecular weight values are obtained, the polyesters show Tg’s of up to 96 °C as well as high Td’s (±315 °C).

One-pot synthesis of new isatin-porphyrin conjugates by the palladium Buchwald-Hartwig methodology involving β-aminoporphyrinatonickel(II) and 3-ketal isatin derivatives

A simple methodology giving rise to a new series of isatin-porphyrin conjugates and corresponding intracyclized derivatives is described. Palladium-catalyzed amination reactions of iodinated isatin derivatives containing the 3-carbonyl group protected with ketal functionalities and 2-amino-5,10,15,20-tetraphenylporphyrinatonickel(II) was the used procedure. The combination of palladium catalysts and the phosphine ligand dicyclohexylphospino-2′,4′,6’-triisopropylbiphenyl (XPhos) led to isatin-porphyrin conjugates in good yields. Nevertheless, the use of palladium acetate even resulted on the formation of additional six membered fused ring compounds. This brings a new perspective to access quinolino[2,3,4-at]porphyrins, a set of compounds which are typically obtained by harsh Cadogan or thermal cyclization approaches.

A Visible-Light-Triggered Conformational Diastereomer Photoswitch in a Bridged Azobenzene.

Ketal-substituted bridged azobenzenes have been synthesized; these display a symmetrical boat conformation with the ketal in pseudo-equatorial positions. These bridged Z-azobenzenes (Z1 ) readily photoisomerize to the E-isomer as well as another Z-conformer (Z2 ) with ketal function on the pseudo-axial position upon irradiation at 406 nm. The two diastereomeric conformers display distinct physicochemical characteristics. Spectroscopic and NMR investigations supported that interconversion of two conformers occurs via the E-isomer, with good photochemical quantum yield (ΦZ1→E =0.45±0.03, ΦE→Z1 =0.33±0.05, ΦE→Z2 =0.37±0.06 and ΦZ2→E =0.36±0.04). The system shows high photostability and no thermal equilibrium between the two stable Z1 and Z2 conformers.

A new rearranged tricyclic abietane diterpenoid from Salvia chloroleuca Rech. f. & Allen

Phytochemical investigation of the roots of Salvia chloroleuca led to the isolation and identification of a new rearranged abietane diterpenoid (1). Its structure was elucidated by interpretation of the 1D and 2D NMR spectra and completed by the analysis of the HR-ESI-MS data. Compound 1 is the secondly reported compound on a rearranged tricyclic abietane (4,5-seco-5,10-friedo-abietane) diterpenoid with a ketal functionality between C-2 and C-11. A plausible biosynthetic pathway of 1 was also proposed.

Stereoselective syntheses of racemic quercitols and bromoquercitols starting from cyclohexa-1,4-diene: gala-, epi-, muco-, and neo-quercitol

The efficient synthesis of gala-, epi-, neo-, and muco-quercitols and some brominated quercitols starting from cyclohexa-1,4-diene is reported. Treatment of the dibromide, obtained by the addition of bromine to cyclohexa-1,4-diene, with m-chloroperbenzoic acid (m-CPBA) yielded the dibromoepoxide, which was successfully converted to the desired dibromodiol by treatment with sulfuric acid. The resulting diol was reacted with 2,2-dimethoxypropane to give the dibromoketal. Hydrogen bromide elimination with NaOMe gave the key compound methoxyketal, rel-(3aS,5R,7aS)-5-methoxy-2,2-dimethyl-3a,4,5,7a-tetrahydrobenzo[d][1,3]dioxole. The second key compound, an isomeric methoxyketal, was prepared by ketalization of 4,5-dibromocyclohexane-1,2-diol with dimethoxypropane followed by the reaction with NaOMe. Deprotection of ketal functionality with sulfuric acid followed by acetylation with acetic anhydride in pyridine resulted in the formation of diacetate rel-(1S,2R,5R)-5-methoxycyclohex-3-ene-1,2-diyl diacetate. Epoxidation of the double bonds in isomeric methoxy diacetates and cis-hydroxylation followed by epoxide-opening and deprotection resulted in the formation of various quercitol derivatives. The inhibition activity of eleven quercitols, methoxyquercitols and bromoquercitols was tested against α-glycosidase.

DDQ-Supported Alkoxylation of 2-Aza-21-carbaporphyrin and Noncatalyzed Transetherification of Its 3,21-Dialkoxy Derivatives

An oxidative addition of primary alkoxyls into two sites of N-confused porphyrin (NCP) has been accomplished by means of alcohols in the presence of a stoichiometric amount of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The resulting aromatic monocationic species 1-R(3) (R = Me, Et) were characterized by the NMR and, in the case of triethoxy-NCP, by monocrystal X-ray diffraction analysis. One alkoxy group is located in position 3, on the macrocycle's perimeter, while two -OR moieties are attached to the internal carbon (position 21) of the confused pyrrole. The 3-EtO-21-Cl-NCP 2, which is formed as a byproduct, was also structurally characterized by means of X-ray diffraction. Reduction of 3-RO-21-(RO)(2)-NCP with hydrazine hydrate gave selectively a neutral and intrinsically chiral 3,21-bis(alkoxy)NCP 3-R(2). Dealkylation of the externally bonded 3-OR fragment under basic conditions leading to a zwitterionic aromatic 3-oxo-species 4-R(2), which still possesses the internal ketal functionality, was established by the NMR and X-ray diffraction methods. An unprecedented transetherification for the internal alkoxyl of 3-R(2) can be achieved under very mild conditions and without catalyst. One of the alkoxyl-exchange products, i.e., 3-ethoxy-21-methoxy-NCP, was characterized by the X-ray diffraction method. The substitution proceeds via an associative (S(N)2) mechanism resulting in an inversion of the chirality of 3-RR', which was shown by means of the NMR and chirooptical methods.

Z-Group Ketone Chain Transfer Agents for RAFT Polymer Nanoparticle Modification via Hydrazone Conjugation

A ketal-containing trithiocarbonyl compound has been synthesized and characterized as a chain transfer agent (CTA) in Reversible Addition Fragmentation Transfer (RAFT) polymerization. The ketal functionality does not interfere with RAFT polymerization of acrylate monomers, which proceeds as previously reported to yield macro-CTA polymers and block co-polymers. Post-polymerization ketal cleavage revealed ketone functionality at the polar terminus of an amphiphilic block co-polymer. Hydrazone-formation was facile in both organic solution as well as in aqueous buffer where polymer nanoparticle assemblies were formed, indicating a conjugation/end-functionalization yield of 40-50%. Conjugation was verified with fluorescein, biotin and Gd-DOTA derivatives, and though the trithiocarbonate linkage is hydrolytically labile, we observed stable conjugation for several days at pH 7.4. and 37°C. As expected, streptavidin binding to biotinylated polymer micelles was observed, and size-change based relaxivity increases were observed when Gd-DOTA hydrazide was conjugated to polymer micelles. Cell-uptake of fluorescently labeled polymer micelles was also readily tracked by FACS and fluorescence microscopy. These polymer derivatives demonstrate a range of potential theranostic/biotechnological applications for this conveniently accessible keto-CTA, which include ligand-based nanoparticle targeting and fluorescent/MR nanoparticle contrast agents.

ChemInform Abstract: Observations on the Use of Triphenylphosphonium Bromide as a Mild and Quantifiable Source of Hydrogen Bromide for Chemoselective Ring Opening of Epoxides to Bromohydrins.

The chemoselective ring opening of epoxides to bromohydrins in the presence of ketal, benzyloxymethoxy and trimethylsilyl ether functionality using triphenylphosphonium bromide is described. The preparation of a polymer supported variant is also reported.

Marinisporolides, Polyene-Polyol Macrolides from a Marine Actinomycete of the New Genus Marinispora

Two new polyene macrolides, marinisporolides A and B (1, 2), were isolated from the saline culture of the marine actinomycete, strain CNQ-140, identified as a member of the new marine genus Marinispora. The marinisporolides are 34-membered macrolides composed of a conjugated pentaene and several pairs of 1,3-dihydroxyl functionalities. Marinisporolide A (1) contains a bicyclic spiro-bis-tetrahydropyran ketal functionality, while marinisporolide B (2) is the corresponding hemiketal. The structures of these new compounds were assigned by combined spectral and chemical methods including extensive 2D NMR experiments and correlations of (13)C NMR data with Kishi's Universal NMR Database. Chemical modifications, including methanolysis, acetonide formation, and application of the modified Mosher method, provided the full stereostructures of these molecules. Three additional macrolides, marinisporolides C-E (3-5), which are olefin geometric isomers of marinisporolide A (1), were also isolated and their structures defined. Under room light, marinisporolides A and B readily photoisomerize to C-E indicating that they are most likely produced by photochemical conversion during the cultivation or isolation procedures. Although polyenes, marinisporolides A (1) and B (2) showed weak to no antifungal activity against Candida albicans.

Surfactants from Biomass: A Two‐Step Cascade Reaction for the Synthesis of Sorbitol Fatty Acid Esters Using Solid Acid Catalysts

Sorbitol fatty esters have been prepared through a two-step catalytic process which involves the protection of the polyalcohol by ketalization followed by esterification with the fatty acid. Inorganic molecular sieves with different pore topologies as well as heteropolyacids (HPA) were used as acid catalysts to perform both the ketalization and the esterification step. These catalysts are found to hydrolyze the ketal function and promote the esterification between the free hydroxy groups and oleic acid in a cascade process. The results show a positive shape-selectivity effect when the process is carried out using tridirectional, and especially monodirectional (mordenite), zeolites, such that the ratio of mono- to higher esters and the hydroxy number of the final product are increased as compared to those obtained for the homogeneous-catalyzed process.

New antiproliferative 14,15-secopregnane glycosides from Solenostemma argel

Eight new 14,15-secopregnane glycosides, namely argelosides C–J, possessing two ketal functions involved in three five-membered rings, have been isolated from the hairy seeds of Solenostemma argel. Their structures have been established by MS and NMR experiments, combined with quantum mechanical calculations of the 13C chemical shifts for the interpretation of the experimental data. On the basis of the obtained results, the structures of argelosides A and B have been revised. Additionally, the effect of these compounds on the VEGF-induced in Kaposi's sarcoma cell proliferation was evaluated. Results indicated that all the compounds reduced the cell proliferation in a dose-dependent manner.

SbCl5—Wet Acetonitrile: A New System for Chemoselective O‐Desilylation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

SbCl 5–wet acetonitrile: a new system for chemoselective O-desilylation

A new efficient method for deprotection of TBDMS derivatives of phenols, primary alcohols, carboxylic acids and secondary amines, consisting of SbCl 5 and MeCN with 0.1% water (w/v), is reported. It effects inter alia desilylation of a CH 2OTBDMS group in the presence of a ketal function.

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