Eng-Chi Wang

A NEW ONE POT METHOD FOR THE CONVERSION OF ALDEHYDES INTO NITRILES USING HYDROXYAMINE AND PHTHALIC ANHYDRIDE

Abstract The aryl and alkyl aldehydes were readily converted to give the corresponding nitriles in good yields using hydroxyamine and phthalic anhydride as reagents in one pot.

A novel synthesis of substituted naphthalenes via Claisen rearrangement and RCM reaction

Abstract A novel synthesis of substituted naphthalenes was studied. Starting from isovanillin, basing on Claisen rearrangement and ring-closing metathesis (RCM), a series of 1-alkoxy-2-methoxynaphthalenes and 1-alkoxy-2-methoxy-8-methylnaphthalenes together with a series of 2-alkoxy-3-methoxynaphthalenes were synthesized.

A new synthesis of 3-alkyl-1-isoindolinones

A new, concise, and efficient method for the synthesis of 3-alkyl-1-isoindolinones was described. 3-Alkyl-3-hydroxy-2,3-dihydro-1-isoindolinones, prepared from the reaction of phthalimide and alkyl lithium, were treated with sodium cyanoborohydride in acidic medium to concomitantly undergo dehydration and reduction leading to various 3-alkyl-1-isoindolinones in good yields.

Versatile Phosphoramidation Reactions for Nucleic Acid Conjugations with Peptides, Proteins, Chromophores, and Biotin Derivatives

Chemical conjugations of nucleic acids with macromolecules or small molecules are common approaches to study nucleic acids in chemistry and biology and to exploit nucleic acids for medical applications. The conjugation of nucleic acids such as oligonucleotides with peptides is especially useful to circumvent cell delivery and specificity problems of oligonucleotides as therapeutic agents. However, current approaches are limited and inefficient in their ability to afford peptide-oligonucleotide conjugates (POCs). Here, we report an effective and reproducible approach to prepare POCs and other nucleic acid conjugates based on a newly developed nucleic acid phosphoramidation method. The development of a new nucleic acid phosphoramidation reaction was achieved by our successful synthesis of a novel amine-containing biotin derivative used to systematically optimize the reactions. The improved phosphoramidation reactions dramatically increased yields of nucleic acid-biotin conjugates up to 80% after 3 h reaction. Any nucleic acids with a terminal phosphate group are suitable reactants in phosphoramidation reactions to conjugate with amine-containing molecules such as biotin and fluorescein derivatives, proteins, and, most importantly, peptides to enable the synthesis of POCs for therapeutic applications. Polymerase chain reactions (PCRs) to study incorporation of biotin or fluorescein-tagged DNA primers into the reaction products demonstrated that appropriate controls of nucleic acid phosphoramidation reactions incur minimum adverse effects on inherited base-pairing characteristics of nucleotides in nucleic acids. The phosphoramidation approach preserves the integrity of hybridization specificity in nucleic acids when preparing POCs. By retaining integrity of the nucleic acids, their effectiveness as therapeutic reagents for gene silencing, gene therapy, and RNA interference is ensured. The potential for POC use was demonstrated by two-step phosphoramidation reactions to successfully synthesize nucleic acid-tetraglycine conjugates. In addition, phosphoramidation reactions provided a facile approach to prepare nucleic acid-BSA conjugates with good yields. In summary, the new approach to phosphoramidation reactions offers a universal method to prepare POCs and other nucleic acid conjugates with high yields in aqueous solutions. The methods can be easily adapted to typical chemistry or biology laboratory setups which will expedite the applications of POCs for basic research and medicine.

Advanced Aqueous-Phase Phosphoramidation Reactions for Effectively Synthesizing Peptide–Oligonucleotide Conjugates Trafficked into a Human Cell Line

Peptide-oligonucleotide conjugates (POCs) have held promise as effective therapeutic agents in treating microbial infections and human genetic diseases including cancers. In clinical applications, POCs are especially useful to circumvent cellular delivery and specificity problems of oligonucleotides. We previously reported that nucleic acid phosphoramidation reactions performed in aqueous solutions have the potential for facile POC synthesis. Here, we carried out further studies to significantly improve aqueous-phase two-step phosphoramidation reaction yield. Optimized reactions were employed to effectively synthesize POCs for delivery into human A549 cells. We achieved optimization of aqueous-phase two-step phosphoramidation reaction and improved reaction yield by (1) determining appropriate co-solutes and co-solute concentrations to acquire higher reaction yields, (2) exploring a different nucleophilicity of imidazole and its derivatives to stabilize essential nucleic acid phosphorimidazolide intermediates prior to POC formation, and (3) enhancing POC synthesis by increasing reactant nucleophilicity. The advanced two-step phosphoramidation reaction was exploited to effectively conjugate a well-studied cell penetrating peptide, the Tat(48-57) peptide, with oligonucleotides, bridged by either no linkers or a disulfide-containing linker, to have the corresponding POC yields of 47-75%. Phosphoramidation-synthesized POCs showed no cytotoxicity to human A549 cells at studied POC concentrations after 24 h inoculation and were successfully trafficked into the human A549 cell line as demonstrated by flow cytometry, fluorescent microscopy, and confocal laser scanning microscopy study. The current report provides insight into aqueous-phase phosphoramidation reactions, the knowledge of which was used to develop effective strategies for synthesizing POCs with crucial applications including therapeutic agents for medicine.

In Vitro Selection and Characterization of a Novel Zn(II)-Dependent Phosphorothiolate Thiolesterase Ribozyme

Here we present the in vitro selection of a novel ribozyme specific for Zn2+-dependent catalysis on hydrolysis of a phosphorothiolate thiolester bond. The ribozyme, called the TW17 ribozyme, was evolved and selected from an artificial RNA pool covalently linked to a biotin-containing substrate through the phosphorothiolate thiolester bond. The secondary structure for the evolved ribozyme consisted of three major helices and three loops. Biochemical and chemical studies of ribozyme-catalyzed reaction products provided evidence that the ribozyme specifically catalyzes hydrolysis of the phosphorothiolate thiolester linkage. A successful ribozyme construct with active catalysis in trans further supported the determined ribozyme structure and indicated the potential of the ribozyme for multiple-substrate turnover. The ribozyme also requires Zn2+ and Mg2+ for maximal catalysis. The TW17 ribozyme, in the presence of Zn2+ and Mg2+, conferred a rate enhancement of at least 5 orders of magnitude when compared to the estimated rate of the uncatalyzed reaction. The ribozyme completely lost catalytic activity in the absence of Zn2+, like Zn2+-dependent protein hydrolases. The discovery and characterization of the TW17 ribozyme suggest additional roles for Zn2+ in ribozyme catalysts.

Acyclic Nucleosides: Synthesis of 1-[(1-Hydroxy-2-Propoxy) Methyl]Thymine, 6-Azathymine, URACIL, AND 6-Azauracil as Potential Antiviral Agents

Abstract A series of acyclic nucleosides have been synthesized. Thymine, 6-azathymine, uracil, and 6-azauracil were silylated with hexamethyldisilazane in the presence of ammonium sulfate and then coupled with 1-benzyloxy-2-chloromethoxypropane to give the corresponding 1-(1-benzyloxy-2-propoxy)methyl derivatives. A minor quantity of benzyloxymethylated product was also obtained in each case. Hydrogenolysis of the protected acyclic nucleosides with palladium(II) hydroxide afforded the title compounds. None of the compounds exhibited significant antiviral activity against human immunodeficiency virus (HIV).

Electrophilic Olefin Heterocyclization in Organic Synthesis. Formation of d-Lactams by Iodine-induced Lactamization of d,e-Unsaturated Thioimidates

The diastereoselective iodine-induced lactamization of δ,e-unsaturated thioimidates (1) accessible from allylation of a dianion of N-benzyl-3-phenylsulfonylpropionamide (3) followed by elaboration gave the substituted δ-lactams (2)

Corroboration of Zn(II)–Mg(II)-tertiary structure interplays essential for the optimal catalysis of a phosphorothiolate thiolesterase ribozyme

The TW17 ribozyme, a catalytic RNA selected from a pool of artificial RNA, is specific for the Zn2+-dependent hydrolysis of a phosphorothiolate thiolester bond. Here, we describe the organic synthesis of both guanosine α-thio-monophosphate and the substrates required for selecting and characterizing the TW17 ribozyme, and for deciphering the catalytic mechanism of the ribozyme. By successively substituting the substrate originally conjugated to the RNA pool with structurally modified substrates, we demonstrated that the TW17 ribozyme specifically catalyzes phosphorothiolate thiolester hydrolysis. Metal titration studies of TW17 ribozyme catalysis in the presence of Zn2+ alone, Zn2+ and Mg2+, and Zn2+ and [Co(NH3)6]3+ supported our findings that Zn2+ is absolutely required for ribozyme catalysis, and indicated that optimal ribozyme catalysis involves the presence of outer-sphere and one inner-sphere Mg2+. A survey of the TW17 ribozyme activity at various pHs revealed that the activity of the ribozyme critically depends on the alkaline conditions. Moreover, a GNRA tetraloop-containing ribozyme constructed with active catalysis in trans provided catalysis and multiple substrate turnover efficiencies significantly higher than ribozymes lacking a GNRA tetraloop. This research supports the essential roles of Zn2+, Mg2+, and a GNRA tetraloop in modulating the TW17 ribozyme structure for optimal ribozyme catalysis, leading also to the formulation of a proposed reaction mechanism for TW17 ribozyme catalysis.

Acyclic Nucleosides Part3: Synthesis of Certain 1-[(1,3-Dihydroxy-2-propoxy)methy1]6-azauracils as Potential Antiviral Agents

The preparation of certain 1-[(1,3-Dihydroxy-2-propoxy) methy1] 6-azauracils, acyclic analogues of antiviral DHPG, is described. A number of 6-azauracils were trimethylsilylated and then coupled with 2-chloromethoxypropane to give 1-[(1,3-Dihydroxy-2-propoxy) methy1] 6-azauracils which were debenzylated with either boron trichloride or palladium oxide to yield the title compounds.