Search

Glycosphingolipids (GSLs) play essential roles in many important biological processes, making them attractive synthetic targets. In this paper, a viable chemoenzymatic method is described for the synthesis of globo-series GSLs, namely, Gb4, Gb5, SSEA-4, and Globo H. The strategy uses a chemically synthesized lactoside acceptor equipped with a partial ceramide structure that is uniquely extended by glycosyltransferases in a highly efficient one-pot multiple enzyme (OPME) procedure. A direct and quantitative conversion of Gb4 sphingosine to Globo H sphingosine is achieved by performing two-sequential OPME glycosylations. A reduction and N-acylation protocol allows facile incorporation of various fatty acids into the lipid portions of the GSLs. The chemically well-defined lipid-modified Globo H-GSLs displayed some differences in their immunosuppressive activities, which may benefit the structural modifications of Globo H ceramides in finding new types of immunosuppressive agents. The strategy outlined in this work should be applicable to the rapid access to other complex GSLs.

Herein, we applied PmST1 (a sialyltransferase) to achieve acceptor-mediated regioselective sialylation (AMRS) on the nonreducing end GalNH2 or GalAz (2-azido-2-deoxy galactose). Thus, C5 and C8-modified sialic acid was efficiently assembled on GalNH2 (or GalAz) to achieve the synthesis of the GAA-7 (one of the echinodermatous gangliosides with higher neuritogenic activity) glycan moiety.

A straightforward synthesis of the α(2→5)-linked 9-O-sulfated Neu5Gc-capped O-linked tetrasaccharide (1) identified in the egg cell surface glycoproteins of the sea urchin Strongylocentrotus purpuratus receptor for sperm is reported. The construction of the α(2→5)Neu5Gc trimer by the formation of an amide linkage rather than a glycosidic bond avoids the requirement for α-stereoselective glycosylation. To highlight this amide bond formation strategy as a relatively facile method for synthesizing oligo-Neu5Gc containing O-linked glycans, its versatility is demonstrated by application to the coupling of SO3H-9Neu5Gcα(2→5)Neu5Gc glycolic acid and a sialyl-Tn-derived amine for achieving the target tetrasaccharide. This synthetic strategy may be implemented in the generation of other structurally similar O-sulfo Neu5Gc-capped α2→5-Oglycolyl-linked oligo-Neu5Gc chains, enabling additional biological and chemical investigations.

Herein, we report a bifunctional sulfo-fluorous affinity (SOFA) tag-assisted enzymatic synthesis and purification strategy for the facile preparation of bioactive glycans using fluorous solid-phase extraction (FSPE). The incorporation of a sulfonate moiety onto the heavy fluorous tag significantly increases its water solubility, which allows the broad use of the inherently hydrophobic fluorous tag in aqueous buffers. In addition, the SOFA tag contains a photocleavable linker, enabling the easy release of amino-functionalized oligosaccharides by UV irradiation. The SOFA tag was used in the synthesis of both negatively charged and neutral glycans to demonstrate its broad utility as an acceptor toward six different glycosyltransferases, significantly improving the feasibility of the preparation of complex glycans using FSPE. All the reactions were performed in an aqueous buffer, a minimum amount of methanol was used to purify the products, and the SOFA tag was easily recovered after photo-irradiation. Thus, the entire synthetic process is environmentally benign.

Sialic-acid-binding, immunoglobulin-type lectin-7 (Siglec-7) is present on the surface of natural killer cells. Siglec-7 shows preference for disialylated glycans, including α(2,8)-α(2,3)-disialic acids or internally branched α(2,6)-NeuAc, such as disialosylglobopentaose (DSGb5). Herein, DSGb5 was synthesized by a one-pot multiple enzyme method from Gb5 by α2,3-sialylation (with PmST1) followed by α2,6-sialylation (with Psp2,6ST) in 23 % overall yield. DSGb5 was also chemoenzymatically synthesized. The protection of the nonreducing-end galactose of Gb5 as 3,4-O-acetonide, 3,4-O-benzylidene, and 4,6-O-benzylidene derivatives provided DSGb5 in overall yields of 26 %, 12 %, and 19 %, respectively. Gb3, Gb4, and Gb5 were enzymatically sialylated to afford a range of globo-glycans. Surprisingly, DSGb5 shows a low affinity for Siglec-7 in a glycan microarray binding affinity assay. Among the synthesized globo-series glycans, α6α3DSGb4 shows the highest binding affinity for Siglec-7.

MicroRNAs (miRNAs) are critical small non-coding RNAs that regulate gene expression by hybridizing to the 3'-untranslated regions (3'-UTR) of target mRNAs, subsequently controlling diverse biological processes at post-transcriptional level. How miRNA genes are regulated receives considerable attention because it directly affects miRNA-mediated gene regulatory networks. Although numerous prediction models were developed for identifying miRNA promoters or transcriptional start sites (TSSs), most of them lack experimental validation and are inadequate to elucidate relationships between miRNA genes and transcription factors (TFs). Here, we integrate three experimental datasets, including cap analysis of gene expression (CAGE) tags, TSS Seq libraries and H3K4me3 chromatin signature derived from high-throughput sequencing analysis of gene initiation, to provide direct evidence of miRNA TSSs, thus establishing an experimental-based resource of human miRNA TSSs, named miRStart. Moreover, a machine-learning-based Support Vector Machine (SVM) model is developed to systematically identify representative TSSs for each miRNA gene. Finally, to demonstrate the effectiveness of the proposed resource, an important human intergenic miRNA, hsa-miR-122, is selected to experimentally validate putative TSS owing to its high expression in a normal liver. In conclusion, this work successfully identified 847 human miRNA TSSs (292 of them are clustered to 70 TSSs of miRNA clusters) based on the utilization of high-throughput sequencing data from TSS-relevant experiments, and establish a valuable resource for biologists in advanced research in miRNA-mediated regulatory networks.

The cyclization reaction of several diallyl aromatic amine molecules, each containing an ethynyl group at the ortho position of the aromatic ring, is accompanied by an aza-Claisen rearrangement, causing an allyl group migration to give substituted indole compounds. This cyclization is catalyzed by ruthenium triphenylphosphine and diphenylphosphinoethane (dppe) complexes as well as gold complexes with silver reagent. The less sterically crowded dppe complex is a more efficient catalyst. The mechanism involving a vinylidene intermediate is proposed on the basis of isolation of several intermediates in the ruthenium-catalyzed system. Single crystals of a metal complex with the cyclized ligand were obtained, and the structure was determined by an X-ray diffraction analysis.

New salt-inclusion lanthanide silicates, [K 9F 2][Ln 3Si 12O 32] (Ln = Sm, Eu, Gd), have been synthesized using a KF-MoO 3 flux, and structurally characterized by single-crystal and powder X-ray diffraction. The structures of these three isostructural compounds consist of open-branched funfer silicate single layers with six-, eight-, and twelve-membered rings, which are connected via LnO 6 octahedra to form a 3-D framework. The F (-) and K (+) ions are located in the structural channels and form a F 2K 7 dimer with a structure similar to that of Cl 2O 7. The photoluminescence properties of the Eu compound have also been studied. The sharp peaks in the room-temperature emission spectrum are assigned and the relative intensities of the (5)D 0 --(7)F 1 and (5)D 0 --(7)F 2 transitions are consistent with the crystallography results. Crystal data for the Eu compound: triclinic, space group P1 (No. 2), a = 6.8989(2) A, b = 11.3834(4) A, c = 11.4955(4) A, alpha = 87.620(2) degrees , beta = 89.532(2) degrees , gamma = 80.221(2) degrees , and Z = 2. Crystal data for the Sm compound: The same as those for the Eu compound except a = 6.9152(6) A, b = 11.400(1) A, c = 11.531(1) A, alpha = 87.610(1) degrees , beta = 89.445(1) degrees , and gamma = 80.081(1) degrees .

New salt-inclusion lanthanide silicates, [K9F2][Ln3Si12O32] (Ln = Sm, Eu, Gd), have been synthesized using a KF-MoO3 flux, and structurally characterized by single-crystal and powder X-ray diffract...

MicroRNAs (miRNAs) are critical small non-coding RNAs that regulate gene expression by hybridizing to the 3′-untranslated regions (3′ UTR) of target mRNAs, subsequently controlling diverse biological processes at posttranscriptional level. How miRNA genes are regulated receives considerable attention because it directly affects miRNA-mediated gene regulatory networks. Although numerous prediction models were developed for identifying miRNA promoters or transcriptional start sites (TSSs), most of them lack experimental validation and are inadequate to elucidate relationships between miRNA genes and transcription factors (TFs). Here, we integrate three experimental datasets, including Cap analysis of gene expression (CAGE) tags, TSS Seq libraries, and H3K4me3 chromatin signature derived from high-throughput sequencing analysis of gene initiation, to provide direct evidence of miRNA TSSs, thus establishing an experimental-based resource of human miRNA TSSs, named miRStart. Moreover, a machine learning based Support Vector Machine (SVM) model is developed to systematically identify representative TSSs for each miRNA gene. Finally, to demonstrate the effectiveness of the proposed resource, an important human intergenic miRNA, hsa-miR-122, is selected to experimentally validate putative TSS owing to its high expression in a normal liver. In conclusion, this work successfully identify 847 human miRNA TSSs (292 of them are clustered to 70 TSSs of miRNA clusters) based on the utilization of high-throughput sequencing data from TSS-relevant experiments, and establish a valuable resource for biologists in advanced research in miRNA-mediated regulatory networks. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4185. doi:1538-7445.AM2012-4185

A new Eu(III) germanate, KEuGe2O6, has been synthesized by both the flux-growth method and the high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction. The compound contains parallel zigzag chains of edge-sharing Eu-O polyhedra, which are in turn linked by sharing vertices and edges with three-membered single ring Ge3O9(6-) germanate anions to form a 3-D framework structure. The magnetic and luminescence properties were also investigated. The observed chiMT value at 300 K is 4.53 emu K mol(-1), which is in good agreement with the calculated value for three Eu3+ ions. The sharp peaks in the room-temperature emission spectrum are assigned. The number of lines in the region of the 5D0--7F0 transition and the relative intensities of the 5D0--7F1 and 5D0--7F2 transitions confirm the presence of two local Eu3+ environments and strongly distorted Eu3+-ligand surroundings. The reasons for the very short emission life time is discussed. The Sm and Tb analogues have also been synthesized.