An efficient synthetic route to glycoamino acid building blocks for glycopeptide synthesis

[reaction: see text] Chemical glycopeptide synthesis requires access to gram quantities of glycosylated amino acid building blocks. Hence, the efficiency of synthesis of such building blocks is of great importance. Here, we report a fast and highly efficient synthetic route to Fmoc-protected asparaginyl glycosides from unprotected sugars in three steps with high yields. The glycosylated amino acids were successfully incorporated into target glycopeptides 7 and 8 by standard Fmoc solid-phase peptide synthesis.     

Stereoselective total synthesis of styryl-lactones: (+)-crassalactones B and C, (+)-howiionol A, (+)-tricinnamate, (+)-goniofufurone and (+)-dicinnamoyl goniofufurone

The total synthesis of (+)-crassalactone B, (+)-crassalactone C, (+)-howiionol A, (+)-tricinnamate, (+)-goniofufurone, and (+)-dicinnamoyl goniofufurone is achieved by a ‘chiron approach’ starting from diacetone d-glucose (DAG). Mitsunobu inversion, Wittig olefination and ring closing metatheses were used as key steps for (+)-howiionol A and (+)-tricinnamate. Meldrum’s acid was used for the synthesis of (+)-crassalactone C, (+)-goniofufurone, and (+)-dicinnamoyl goniofufurone. Yamaguchi esterification was used for (+)-crassalactone B, while a Grignard reaction followed by concomitant deallylation was first reported in the synthesis of (+)-dicinnamoyl goniofufurone.     

Highly efficient CuI-catalyzed coupling of aryl bromides with oxazolidinones using Buchwald's protocol: a short route to linezolid and toloxatone

[reaction: see text] Coupling of a variety of substituted aryl bromides with oxazolidinones has been achieved using the Buchwald protocol for the amidation of aryl halides. This procedure is exemplified by the synthesis of two medicinally important molecules, linezolid and toloxatone.     

Synthesis of novel twisted carbazole-quinoxaline derivatives with 1,3,5-benzene core: bipolar molecules as hosts for phosphorescent OLEDs

A series of carbazole/quinoxaline hybrids have been synthesized by classic Ullmann and Pd/Cu-catalyzed Sonogashira coupling reaction. Their photophysical, thermal, and electrochemical properties were investigated. The introduction of electron rich carbazole and electron deficient quinoxaline on to the 1,3,5-benzene center leads to a twisted structure with good glass forming property and imparts a bipolar character. The triplet energies in the range of 2.34-2.53 eV indicate them as potential host materials in phosphorescent OLEDs.     

Synthesis and Characterization of Donor–π‐Acceptor‐Based Porphyrin Sensitizers: Potential Application of Dye‐Sensitized Solar Cells

New porphyrin sensitizers based on donor–π‐acceptor (D‐π‐A) approach have been designed, synthesized, characterized by various spectroscopic techniques and their photovoltaic properties explored. N,N′‐Diphenylamine acts as donor, the porphyrin is the π‐spacer, and either carboxylic acid or cyanoacryclic acid acts as acceptor. All compounds were characterized by using ¹H NMR spectroscopy, ESI‐MS, UV–visible emission spectroscopies as well as electrochemical methods. The presence of aromatic groups between porphyrin π‐plane and acceptor group push the absorption of both Soret and Q‐bands of porphyrin towards the red region. The electrochemical properties suggests that LUMO of these sensitizers above the TiO₂ conduction band. Finally, the device was fabricated using liquid redox electrolyte (I^?/I₃^?) and its efficiency was compared with that of a leading sensitizer.     

Studies directed toward the first total synthesis of acremodiol and acremonol

Studies directed toward the synthesis of acremodiol and acremonol resulted in the synthesis of two macrodiolides 1, 1a, and 2 besides 3. The attempted synthesis of 1 and 2 confirmed that the absolute stereochemistry defined in the earlier report is incorrect. Compound 1 was synthesized by RCM-mediated macrocyclization. Attempted synthesis of 2 failed to give good yields in the cyclization, and 1a and 2 were synthesized by the Yamaguchi macrolactonization method.     

Quinoxaline‐based D‐A conjugated polymers for organic solar cells: Probing the effect of quinoxaline side chains and fluorine substitution on the power conversion efficiency

We describe the successful synthesis of four novel donor‐acceptor (D‐A) type copolymers, referred to as PQxBT , PQxFBT , TQxBT , and TQxFBT . The effects of using a fluorinated bithiophene (FBT) and varying the side‐chain moieties tethered to the quinoxaline (Qx) unit (electron‐withdrawing group in the polymer backbone) on the physical properties and photovoltaic performance were investigated. Specifically, the four polymers were synthesized using either alkoxyphenyl (P) or alkylthiophene (T) units anchored to the quinoxaline in the polymer backbone. The FBT‐bearing polymers, PQxFBT and TQxFBT , displayed more redshifted absorption spectra and higher crystallinity owing to the greater planarity of their polymer backbone as compared to the non‐fluorinated polymers. The TQxFBT copolymer, equipped with both the alkylthiophene side chains and FBT, exhibited face‐on orientation in film state and a well‐mixed nanophase morphology in TQxFBT :PC₇₁BM blend films. The photovoltaic device fabricated from TQxFBT :PC₇₁BM exhibited the highest power conversion efficiency of 4.18%. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1209–1218     

Primes in sumsets

We obtain an upper bound for the number of pairs \( (a,b) \in {A\times B} \) such that \( a+b \) is a prime number, where \( A, B \subseteq \{1,\ldots ,N \}\) with \(|A||B| \, \gg \frac{N^2}{(\log {N})^2}\), \(\, N \ge 1\) an integer. This improves on a bound given by Balog, Rivat, and Sárközy.     

Enzyme-cleavable linkers for peptide and glycopeptide synthesis

Hydroxymethylphenoxy linkers that are commonly used in solid phase peptide synthesis are surprisingly susceptible to efficient cleavage by the protease chymotrypsin with a broad range of amino acid residues being tolerated at the scissile bond; this enzyme-cleavable linker system has been applied to peptide and glycopeptide synthesis.