Design and synthesis of novel χ2-constrained phenylalanine, naphthylalanine, and tryptophan analogues and their use in biologically active melanotropin peptides

Palladium-Catalyzed Aminocyclization-Coupling Cascades: Preparation of Dehydrotryptophan Derivatives and Computational Study

Dehydrotryptophan derivatives have been prepared by palladium-catalyzed aminocyclization-Heck-type coupling cascades starting from o-alkynylaniline derivatives and methyl α-aminoacrylate. Aryl, alkyl (primary, secondary, and tertiary), and alkenyl substituents have been introduced at the indole C-2 position. Further variations at the indole benzene ring, as well as the C-2-unsubstituted case, have all been demonstrated. In the case of C-2 aryl substitution, the preparation of the o-alkynylaniline substrate by Sonogashira coupling and the subsequent cyclization-coupling cascade have been performed in a one-pot protocol with a single catalyst. DFT calculations have revealed significant differences in the reaction profiles of these reactions relative to those involving methyl acrylate or methacrylate, and between the reactions of the free anilines and their corresponding carbamates. Those calculations suggest that the nature of the alkene and of the acid HX released in the HX/alkene exchange step that precedes C-C bond formation could be responsible for the experimentally observed differences in reaction efficiencies.

Additive-Free Pd-Catalysed C-2 Arylation of Tryptophan Derivatives with Diaryliodonium Salts

An efficient, mild and Pd-catalysed C-2 arylation of Fmoc-L-tryptophan with diaryliodonium salts has been developed, giving easy access to C-2 arylated tryptophan derivatives. This protocol tolerates a variety of functional groups and proceeds smoothly in high yields without any additives. In addition, the chemoseletive C–H arylation with unsymmetrical salts is described.

The stereoselectivity and hydrolysis efficiency of recombinant D-hydantoinase from Vigna angularis Against 5-benzylhydantoin derivatives with halogen and methyl substituents

The researches on D-hydantoinase activity and substrate specificity towards dihydropyrimidine and hydantoin derivatives have been carried out intensively over the last few decades. So far, the major efforts have focused on (R,S)-5-phenylhydantoin and (R,S)-5-(4-hydroxyphenyl)hydantoin, the most desirable D-hydantoinase substrates from pharmaceutical industry point of view. However, it was shown that D-hydantoinase is a substrate-dependent enzyme, and its activity and stereoselectivity towards 5-monosubstituted hydantoins varied significantly with the type of substrate and the source of the enzyme. The aim of this study was to estimate the substrate specificity of D-hydantoinase towards series of 5-benzylhydantoin derivatives with halogen and methyl substituents in the phenyl ring. The biotransformations were carried out by using commercial enzyme: immobilized, recombinant, cloned, and expressed in Escherichia coli D-hydantoinase from Vigna angularis (rD-HYD). All reactions were monitored by capillary electrophoresis (CE), and the conversion yields were calculated. Additionally, enantiomeric ratios of the obtained D-phenylalanine derivatives were estimated by chiral high-performance liquid chromatography (HPLC). Interestingly, the differences in the activities of examined enzyme towards particular 5-benzylhydantoin derivatives were observed. CE was also shown as a promising method for monitoring the hydrolysis of new substrates by D-hydantoinase and further analyzing of enzyme substrate specificity.

Organic chemistry and biology: chemical biology through the eyes of collaboration

From a scientific perspective, efforts to understand biology including what constitutes health and disease has become a chemical problem. However, chemists and biologists "see" the problems of understanding biology from different perspectives, and this has retarded progress in solving the problems especially as they relate to health and disease. This suggests that close collaboration between chemists and biologists is not only necessary but essential for progress in both the biology and chemistry that will provide solutions to the global questions of biology. This perspective has directed my scientific efforts for the past 45 years, and in this overview I provide my perspective of how the applications of synthetic chemistry, structural design, and numerous other chemical principles have intersected in my collaborations with biologists to provide new tools, new science, and new insights that were only made possible and fruitful by these collaborations.

The first preparative solution phase synthesis of melanotan II

Melanotan II is a synthetic cyclic heptapeptide used to prevent a sunlight-induced skin cancer by stimulating the skin tanning process. In this paper we report the first solution phase synthesis of the title compound. The hexapeptide sequence has been assembled by [(2+2)+1+1] scheme. After removing the orthogonal protection, a carbodiimide mediated lactamization, involving the ε-amino group of lysine and γ-carboxy group of aspartic acid, led to a cyclic intermediate. Appending N-acetylnorleucine concluded the assembly of melanotan II molecule. Protection of the lateral groups in arginine and tryptophan was omitted for atom and step economy reasons. The total synthesis of melanotan II was accomplished in 12 steps with 2.6% overall yield, affording >90% pure peptide without using preparative chromatography.

Synthesis and evaluation of new arylbenzo[b]thiophene and diarylthiophene derivatives as inhibitors of the NorA multidrug transporter of Staphylococcus aureus

The synthesis based on palladium catalytic coupling of 38 new-arylated benzo[b]thiophenes or thiophenes is described in a few steps. We also report the direct arylation of the position 3 of the benzo[b]thiophenic structure, a 'one pot' 2,5-heterodiarylation of thiophenes as well as the synthesis of precursors of amino-acids with a 2-arylated benzo[b]thiophene core. These compounds were evaluated on bacteria strains: most of them did not exhibit any antibiotic activity but were found to selectively inhibit the NorA multidrug transporter of Staphylococcus aureus. As such, they restored the activity of the NorA substrates ciprofloxacin against a resistant S. aureus strain in which this efflux pump is over-expressed.

Design, synthesis, and biological evaluation of a new class of small molecule peptide mimetics targeting the melanocortin receptors

A new bicyclic template has been developed for the synthesis of peptide mimetics. Straightforward synthetic steps, starting from amino acids, allow the facile construction of a wide range of analogs. This system was designed to target the melanocortin receptors (MCRs), with functional group selection based on a known pharmacophore and guidance from molecular modeling to rationally identify positional and stereochemical isomers likely to be active. The functions of hMCRs are critical to myriad biological activities, including pigmentation, steroidogenesis, energy homeostasis, erectile activity, and inflammation. These G-protein-coupled receptors (GPCRs) are targets for drug discovery in a number of areas, including cancer, pain, and obesity therapeutics. All compounds from this series tested to date are antagonists which bind with high affinity. Importantly, many are highly selective for a particular MCR subtype, including some of the first completely hMC5R-selective antagonists reported.

Solid-phase combinatorial synthesis of peptide-biphenyl hybrids as calpain inhibitors

[structure: see text] The combinatorial parallel synthesis of peptide-biphenyl hybrids on solid support using state of the art of peptide synthesis is reported. Key steps were the N to C addition of an amino moiety, hydrolysis of the methyl ester, and the absence of cross-linked compounds when the 2,2'-diamino-1,1'-biphenyl was incorporated. When tested for activity as calpain inhibitors, some of the compounds exhibited IC(50) values in the nanomolar range.

Model studies toward the synthesis of dihydropyrimidinyl and pyridyl alpha-amino acids via three-component Biginelli and Hantzsch cyclocondensations

A novel and versatile strategy for the synthesis of heterocyclic alpha-amino acids has been described. The use of components (aldehyde or beta-ketoester) bearing a masked glycinyl moiety in Biginelli and Hantzsch cyclocondensations allowed access to the 4-dihydropyrimidinyl-alpha-glycines, 4-dihydropyrimidinyl-alpha-alanines, 4-pyridyl-alpha-alanines, and 2-pyridyl-alpha-alanines classes. Dihydropyrimidinyl-amino acids were obtained as a mixture of diastereoisomers due to the formation of the stereocenter at C4 of the dihydropyrimidinone ring. Individual stereoisomers were isolated as pure compounds and their structures were assigned with the aid of X-ray crystallography and chiroptical properties. The enantiomeric purity of a representative selection of the above amino acids was greater than 96% as verified by derivatization to the corresponding Mosher's amides and subsequent (1)H and (19)F NMR spectroscopy. Incorporation of the 4-pyridyl-alpha-alanine derivative into a peptide chain is also described.