Solid phase synthesis of 5-aminopyrazoles and derivatives

The development of a novel solid phase synthesis of some 5-aminopyrazoles and derivatives is described. Reaction of hydrazines with solid supported β-keto-nitrile (1) affords 5-aminopyrazoles (2) the amino group of which is readily acylated or sulphonylated. Generation of the solid supported β-keto-nitrile (1) is non trivial and represents a key step in the overall synthesis.     

Solid phase synthesis of two muramyl pentapeptide derivatives

Solid phase peptide synthesis (SPPS) of two selected muramyl pentapeptide derivatives is described. The simplicity of removing the protecting groups via one-step deprotection and cleavage from the resin is the biggest advantage of SPPS. Using this method, two muramyl pentapeptide derivatives, D-MurN₃-L-Ala-D-iGlu-L-Lys-D-Ala-D-Ser (5) and D-MurN₃-L-Ala-D-iGlu-L-Lys-D-Ala-D-Ala (6), were obtained. Their chemical structures were confirmed by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) spectroscopy. To determine the absolute configuration of the carbon atom in the side chain of the muramic acid derivative, single-crystal X-ray diffraction measurements were recorded.     

Gold-catalyzed cyclizations of alkynol-based compounds: synthesis of natural products and derivatives

The last decade has witnessed dramatic growth in the number of reactions catalyzed by gold complexes because of their powerful soft Lewis acid nature. In particular, the gold-catalyzed activation of propargylic compounds has progressively emerged in recent years. Some of these gold-catalyzed reactions in alkynes have been optimized and show significant utility in organic synthesis. Thus, apart from significant methodology work, in the meantime gold-catalyzed cyclizations in alkynol derivatives have become an efficient tool in total synthesis. However, there is a lack of specific review articles covering the joined importance of both gold salts and alkynol-based compounds for the synthesis of natural products and derivatives. The aim of this Review is to survey the chemistry of alkynol derivatives under gold-catalyzed cyclization conditions and its utility in total synthesis, concentrating on the advances that have been made in the last decade, and in particular in the last quinquennium.     

Solid phase synthesis of a cyclic peptide using fmoc chemistry

Using the Fmoc protection strategy of solid phase peptide synthesis, a 10 amino acid peptide was prepared and cyclized in a “head-to-tail” fashion while it was attached to the solid support. Cyclization was accomplished with either BOP or carbodiimide and the peptide was cleaved from the resin and purified using standard protocols.     

Fine synthetic nucleoside chemistry based on nucleoside natural products synthesis

Synthetic nucleoside chemistry based on nucleoside natural products synthesis were described. First, a samarium diiodide (SmI 2)-promoted aldol reaction with the use of alpha-phenylthioketone as an enolate was developed. The characteristics of this reaction are that the enolate can be regioselectively generated and the aldol reaction proceeds under near neutral condition. This reaction is proved to be a powerful reaction for the synthesis of complex nucleoside natural products, and herbicidin B and fully protected tunicaminyluracil, which were undecose nucleoside natural products, were synthesized. Next, the synthetic methodology of the caprazamycins, which are promising antibacterial nucleoside natural products, was also developed by the strategy including beta-selective ribosylation without using a neighboring group participation. Our synthetic route provided a range of key analogues with partial structures to define the pharmacophore. Simplification of the caprazamycins was further pursued to develop diketopiperazine analogs.     

Protein secondary structure templates derived from bioactive natural products – Combinatorial chemistry meets structure-based design

Lead finding strategies in pharmaceutical research comprise structure-based drug design as well as screening efforts of natural product pools or large chemical libraries. In this context we propose a combined approach by utilizing natural product-derived structure information on receptor- or enzyme-complementarity for designing unique core structures that can be employed as privileged template molecules underlying combinatorial libraries. A set of rules for the transformation of molecular frameworks from natural products to structurally defined peptidomimetics is introduced. Special emphasis is laid on the correspondence in the orientational properties and functionalization patterns between natural products and regular protein secondary structures.     

Editorial: natural products chemistry in China

China is a country rich in plants and microbe species that cultivate a remarkable diversity of secondary metabolites. Such products include 'qinghaosu' (artemisinin) and huperzine A, which are used in the treatment of malaria and Alzheimer's disease, respectively.     

Stereoselective total synthesis of C2-symmetric natural products pyrenophorol and its derivatives

Abstract

A stereoselective total synthesis of 16-membered C₂-symmetric macrodiolide Pyrenophorol, Tetrahydropyrenophorol and 4,4-diacetylpyrenophorol have been accomplished. The synthesis started from commercially available L-Aspartic acid and the key reactions involved are regioselective epoxide opening, CBS reduction, Pinnick oxidation and Mitsunobu dilactonization.     

固相有机合成

综述了近年来固相有机合成中采用的连接分子和连接策略及固相合成在有机合成中的应用。     

Solid phase synthesis and opioid receptor binding properties of presumable dermorphin precursor derivatives.

Presumable dermorphin precursor peptide derivatives comprised of 35 amino acids and their fragments, which are based on the amino acid sequence determined by recombinant deoxyribonucleic acid (DNA) techniques, were synthesized by the solid phase method. A 35-residue peptide amide containing L-Ala2-dermorphin sequence at the N-terminus (1) as well as its D-Ala2 isomer (2) and the C-terminal 20-residue peptide amide were found to be unexpectedly stable against aminopeptidase M digestion and in rat brain membrane fractions mixture, suggesting that the C-terminal Glu-rich moiety of 1 and 2 serves to protect from enzymatic breakdown. In the opioid receptor binding assay, 2 showed 40 and 25-fold higher affinities than 1 for mu and delta-receptors, respectively. The N-terminal 15-residue peptide fragment of 2 showed greatly increased affinities for both receptors, being one half of those of dermorphin, whereas that of 1 showed low affinities. Opioid receptor binding properties of these synthetic peptides may be useful in investigation of the processing to dermorphin.     

Solid phase synthesis of praziquantel

The first solid phase synthesis of the important anthelmintic praziquantel is described. The synthesis is rapid and efficient. The method may be extended to the synthesis of libraries of urgently needed replacements for this drug.     

Solid phase synthesis of cyclopropenes

Cyclopropene derivatives of high purity were prepared by reaction of acetylenes with a rhodium carbenoid bound to a polystyrene resin. This solid phase method avoids the formation of undesired byproducts obtained in the corresponding solution reaction and an eventual extension to combinatorial synthesis of cyclopropene derivatives could be achieved.     

Solid phase synthesis of pyridine-based derivatives from a 2-chloro-5-bromopyridine scaffold

2-Chloro-5-bromopyridine was immobilized on polystyrene via selective introduction of a traceless silicon linker at the C-4 position. A useful scaffold was thus obtained, as demonstrated by efficient and selective reactions with polar and transition organometallic reagents, opening a new access to pyridine-based libraries of synthons and chromophores.     

Intramolecular Diels-Alder reaction leading to tricyclic derivatives as intermediates of natural products synthesis

Tricyclic compounds 4a and 4b possessing a bicyclo[4.3.0] moiety, were successfully synthesized by using the intramolecular Diels-Alder reaction. The siloxy- rather than acyloxy-substituents increased the ratio of the endo-cylcoadducts 10 and 12. The oxygen substitution of 9 influenced conformation of the transition state, which was stereochemically restricted by the butenolide moiety. In addition, 9b carrying a hydroxyl group also produced 10b in a similar ratio to 9a. Compound 11 was the only exo-adduct produced in all of the entries.     

Combinatorial synthesis of star-shaped block copolymers: host-guest chemistry of unimolecular reversed micelles

The combination of combinatorial techniques for the synthesis as well as for the screening of novel star-shaped block copolymers consisting of a poly(ethylene glycol) core and a poly(caprolactone) shell leads to a fast evaluation of interesting properties of these materials. The polymers could be synthesized in a fully automated parallel fashion, and the screening of their host-guest properties was accomplished by utilizing a UV/vis plate reader extraction assay. The investigated polymers revealed unimolecular micellar behavior, and their maximum loading capacity could be correlated to their chemical structure. This opens avenues to an improved understanding of the requirements for unimolecular micellar behavior. Furthermore, the accelerated findings clearly point out the advantages of applied combinatorial approaches.     

Solid phase synthesis of 4-hydroxycinnamic acid and its derivatives for potential use in combinatorial chemistry: a novel route for the synthesis of 4-hydroxycinnamoyl coenzyme A and NMDA receptor antagonists

Synthesis of 4-hydroxycinnamic acid 6 and its N-hydroxysuccinimide ester 8 has been carried out in high yield on solid support. Further development allowed the synthesis of 4-hydroxycinnamoyl CoA 1 in excellent overall yield. The utility of solid phase as a method for the synthesis of 4-hydroxycinnamic acid derivatives was demonstrated by the synthesis of a number of compounds including the NMDA receptor antagonists, N-(phenylalkyl)cinnamides 9 and 10.     

Solid phase synthesis of benzothiazole and thiophene derivatives based on resin-bound cyclic malonic acid ester

A new method for the solid phase synthesis of benzothiazoles and 2-arylamino-3-carboxyl-4-hydroxy-5-arylthiophenes is described. Resin bound cyclic malonic acid ester was reacted with aryl isothiocyanates and then with bromine or α-bromoketones, followed by treatment with perchloric acid or sodium methoxide to afford substituted 2-methylbenzothiazoles or 2-arylamino-3-carboxyl-4-hydroxy-5-arylthiophenes, respectively, in high yields and purities.