Total Synthesis (Organic Chemistry)

In a cheap and eco-friendly process, primary and secondary alcohols were easily protected as bis(methoxyphenyl)methyl (BMPM) ethers in good yields using CuBr 2 as a catalyst in acetonitrile at room temperature. Deprotection could easily be achieved using the same catalyst but in ethanol. Both Cu-cat-alyzed protection and deprotection were orthogonal to other methods and fully compatible with other functional groups.

Phase-transfer catalyst (PTC) has been popular for more than four decades in synthetic chemistry. The PT catalysis uses the PTC in a catalytic amount and it allows to react the reactants of two different phases via facilitating transfer of reactants from interface, which are not miscible and itself regenerated again and the cycle is repeated. The use of PTC is wide from liquid-liquid, solid-liquid to liquid-gas system. Due to its diversified application, PTC is also combined with other rate enhancing techniques like microwave, electro-organic synthesis, sono-chemistry, photochemistry and many more are exploring. The PTC application in the field of manufacturing of the fine chemicals and organic intermediates are unlimited.

A practical synthesis of (AE)-pterosin A from commercially available 2-bromo-1,3-dimethyl-benzene 5 has been accomplished in 10% overall yield. The synthesis used SuzukieMiyaura coupling reaction of C6-bromoindanone derivative 3 with potassium vinyltrifluoroborate 9, which provided the corresponding vinylindanone 2 in >85% yield. The vinylindanone 2 could be further elaborated to pterosin A by reduction with LAH, selective protection of primary alcohol with TESCl, hydroborationeoxidation of vinyl group, protection of primary alcohol with TIPSCl, oxidation of the secondary alcohol, and desilylation with TBAF.

We have quantum chemically investigated how solvation influences the competition between the SN2 and E2 pathways of the model F– + C2H5Cl reaction. The system is solvated in a stepwise manner by going from the gas phase, then via microsolvation of one to three explicit solvent molecules, then last to bulk solvation using relativistic density functional theory at (COSMO)-ZORA-OLYP/QZ4P. We explain how and why the mechanistic pathway of the system shifts from E2 in the gas phase to SN2 upon strong solvation of the Lewis base (i.e., nucleophile/protophile). The E2 pathway is preferred under weak solvation of the system by dichloromethane, whereas a switch in reactivity from E2 to SN2 is observed under strong solvation by water. Our activation strain and Kohn–Sham molecular orbital analyses reveal that solvation of the Lewis base has a significant impact on the strength of the Lewis base. We show how strong solvation furnishes a weaker Lewis base that is unable to overcome the high characteristic distortivity associated with the E2 pathway, and thus the SN2 pathway becomes viable.

Total Synthesis of (+)-Phyllanthocin Summary: A convergent, enantioselective total synthesis of (+)-phyllanthocin (1) has been accomplished, incorporating asymmetric epoxidation, directed-aldol condensation , and Rh(1)-catalyzed hydroformylation as key synthetic steps.

The bis-tetrahydroisoquinoline (bis-THIQ) natural products have been studied intensively over the past four decades for their exceptionally potent anticancer activity, in addition to strong gram-positive and -negative antibiotic character. Synthetic strategies toward these complex polycyclic compounds have relied heavily on electrophilic aromatic chemistry, such as the Pictet-Spengler reaction, that mimics their biosynthetic pathways. Herein we report an approach to two bis-THIQ natural products, jorunnamycin A and jorumycin, that instead harnesses the power of modern transition-metal catalysis for the three major bond-forming events and proceeds with high efficiency (15 and 16 steps, respectively). By breaking from biomimicry, this strategy allows for the preparation of a more diverse set of non-natural analogs.

The synthesis, characterization and spectroscopic studies of compounds 6a–g with analgesic activity is described. A new model of interaction between the drug and the enzyme is suggested. Application of the Resonance Valence Bond theory led us to propose, for the first time, an entirely new mechanism involving an electron transfer from the amino acid residue of the enzyme to the drug. Theoretical studies of various transition states involved in the interaction mechanism employing the semi-empirical molecular orbital calculations (AM1 method) have been carried out. This article also deals with an extensive study of the structure–activity relationships of seven oxadiazolo-phthalimides 6a–g.

ABSTRACT: We report on the linear viscoelastic properties of a family of entangled linear thermoplastic nonpolar hybrid inorganic-organic polymers: random copolymers of polystyrene (PS) and styryl-based polyhedral oligosilsesquioxane (POSS), R7(Si8O12)(C6H4CHdCH2), with R) isobutyl (iBu). A series of styrene-styryl POSS random copolymers with 0, 6, 15, 30, and 50 wt % iBuPOSS were investigated. WAXS and TEM demonstrate that the iBuPOSS disperses in the polymeric matrix at a molecular level. It is observed that the iBuPOSS plays a plasticizer-like effect, yielding a monotonic decrease of the glass-transition temperature with increasing iBuPOSS content. Rheological measurements revealed that linear viscoelastic behavior of the copolymers is also profoundly influenced by the presence of iBuPOSS. The incorporation of iBuPOSS dramatically decreases the rubbery plateau modulus (GNo), suggesting a strong dilation effect of isobutyl-POSS on entanglement density. Additionally, the apparent f...

A set of model nucleophiles of gradually changing nucleophilicity is used to probe the glycosylation reaction mechanism. Glycosylations of ethanol-based acceptors, bearing varying amounts of fluorine atoms, report on the dependency of the stereochemistry in condensation reactions on the nucleophilicity of the acceptor. Three different glycosylation systems were scrutinized, that differ in the reaction mechanism, that – putatively – prevails during the coupling reaction. It is revealed that the stereoselectivity in glycosylations of benzylidene protected glucose donors are very susceptible to acceptor nucleophilicity whereas condensations of benzylidene mannose and mannuronic acid donors represent more robust glycosylation systems in terms of diastereoselectivity. The change in stereoselectivity with decreasing acceptor nucleophilicity is related to a change in reaction mechanism shifting from the SN2 side to the SN1 side of the reactivity spectrum. Carbohydrate acceptors are examined and the reactivity–selectivity profile of these nucleophiles mirrored those of the model acceptors studied. The set of model ethanol acceptors thus provides a simple and effective “toolbox” to investigate glycosylation reaction mechanisms and report on the robustness of glycosylation protocols.

The mechanism of the Lewis base F– catalyzed 1,3-dipolar cycloaddition between CO2 and nitrilimines is interrogated using DFT calculations. F– activates the nitrilimine, not CO2 as proposed in the literature, and imparts a significant rate enhancement for the cycloaddition. The origin of this catalysis is in the strength of the primary orbital interactions between the reactants. The Lewis base activated nitrilimine–F– has high-lying filled FMOs. The smaller FMO-LUMO gap promotes a rapid nucleophilic attack and overall cycloaddition with CO2.

Traditional System-on-Chip (SoC) design employed shared buses for data transfer among various subsystems. As SoCs become more complex involving a larger number of subsystems, traditional bus-based architecture is giving way to a new paradigm for on-chip communication. This paradigm is called Network-on-Chip (NoC). A communication network of point-to-point links and routing switches is used to facilitate communication between subsystems. The routing switch proposed in this paper consists of four components, namely the input ports, output ports, switching fabric, and scheduler. The scheduler design is described in this paper. The function of the scheduler is to arbitrate between requests by data packets for use of the switching fabric. The scheduler uses an improved round robin based arbitration algorithm. Due to the symmetric structure of the scheduler, an area-efficient design is proposed by folding the scheduler onto itself, thereby reducing its area roughly by 50%.

The assembly of complex bacterial glycans presenting rare structural motifs and cis-glycosidic linkages is significantly obstructed by the lack of knowledge of the reactivity of the constituting building blocks and the stereoselectivity of the reactions in which they partake. We here report a strategy to map the reactivity of carbohydrate building blocks and apply it to understand the reactivity of the bacterial sugar, caryophyllose, a rare C12-monosaccharide, containing a characteristic tetrasubstituted stereocenter. We mapped reactivity–stereoselectivity relationships for caryophyllose donor and acceptor glycosides by a systematic series of glycosylations in combination with the detection and characterization of different reactive intermediates using experimental and computational techniques. The insights garnered from these studies enabled the rational design of building blocks with the required properties to assemble mycobacterial lipooligosaccharide fragments of M. marinum.

This review aims to provide overall aspects of the history, biology, chemistry and the total synthesis of Aflavinines. The origin of this molecule traced back from the isolation and structural elucidation by Clardy and co-workers in 1980 [Tetrahed. Lett. 1980;21:243-246]. Most of the previously published total syntheses were covered in a brief summary and the key points of each work are highlighted. Moreover, various antiinsectant and antiviral Aflavinines congener are presented. This review is almost the first in Aflavinine topics covering all aspects in brief, to the best of our knowledge.