Preparation of oligodeoxyribonucleoside phosphorodithioates by a triester method.

A method to prepare thymidine phosphorodithioate dimers (ref. 1) has been extended to allow the preparation of oligo-2'-deoxyribonucleotide phosphorodithioates containing all four bases. The method is suitable for large-scale synthesis and gives phosphorodithioates without phosphorothioate impurities (31P nmr, detection limit 0.5 to 1%). Oligonucleotides up to octamers which contain -0-(PS2-)-0- linkages at all positions have been prepared by block synthesis in solution. The phosphorodithioate linkage is introduced by the reaction of a 5'-O, N-protected nucleoside (or oligonucleotide) with a dithiophosphorylating agent RSP(S)(ODhbt)2, R = 2,4-dichlorobenzyl, Dhbt = 3,4-dihydro-4-oxo-benzotriazin-3-yl, followed by coupling of the product to a 3'-O,N-protected nucleoside (or oligonucleotide). This method gives pure protected oligodeoxyribonucleoside phosphorodithioates, and phosphorothioate linkages are only introduced if contact with conc. aqueous ammonia during or after deblocking is unduly prolonged.     

Synthesis of N-protected peptide alcohols catalyzed by subtilisin or alpha-chymotrypsin in organic solvents

A series of N-protected peptide alcohols were synthesized using amino alcohols with unprotected hydroxy groups as amino components by the catalysis of subtilisin or alpha-chymotrypsin in organic solvents. N-protected aromatic amino acid esters were more suitable as acyl donors for subtilisin. The influences of different N-protecting groups, organic solvents, and content of water on synthesis of N-protected peptide alcohols were systematically studied.     

Modified PNAs: a simple method for the synthesis of monomeric building blocks

The synthesis of PNA-monomers with variations in the substitution pattern using the Ugi-Reaction is described. The one-pot procedure leads to new totally protected PNA-monomers which can be selectively cleaved to N-protected monomeric building blocks for PNA synthesis.     

Synthesis of sequential polydepsipeptides utilizing a new approach for the synthesis of depsipeptides

Sequential polydepsipeptides were synthesized by the depsipeptide active ester method using a new approach for the direct synthesis of N-protected depsipeptide free acids from hydroxy acids. The method uses synthesis of Boc-didepsipeptides by reaction of free hydroxy acids with Boc-amino acid N-hydroxysuccinimide esters catalyzed by 4-dimethylaminopyridine and chain elongation of the free depsipeptides by the reaction with Boc-amino acid N-hydroxysuccinimide esters in an organic solvent system of acetonitrile-tetrahydrofuran. The Boc-depsipeptide free acids were activated as their N-hydroxysuccinimide esters, which were polymerized after removal of the Boc-protecting group.     

A short, efficient synthesis of 2'-deoxypseudoisocytidine based on Heck-chemistry

A novel synthesis of 2'-deoxypseudoisocytidine as well as of its phosphoramidite building block for oligonucleotide synthesis is presented. The synthesis is based on Heck-coupling between N-protected pseudoisocytosine and a silyl protected furanoid glycal. With this procedure the corresponding phosphoramidite building block is obtained in 5 steps and an overall yield of 28%.     

Synthesis of chiral N-protected amino acid esters by the use of UNCAs

Summary An easy synthesis of N-protected amino acid esters, including tert-butyl esters, is described by the use of urethane N-protected carboxyanhydrides (UNCAs). Treating UNCAs with tert-butanol in the presence of potassium bicarbonate at 45°C yielded the corresponding N-protected amino acid tert-butyl esters in a very simple way. Benzyloxycarbonyl and tert-butyloxycarbonyl N-protected amino acid tert-butyl esters have been obtained by this procedure. Once more, this reaction showed the great reactivity of UNCAs.     

A Short,Efficient Synthesis of 2′-Deoxypseudoisocytidine Based on Heck-Chemistry

Abstract

A novel synthesis of 2′-deoxypseudoisocytidine as well as of its phosphoramidite building block for oligonucleotide synthesis is presented. The synthesis is based on Heck-coupling between N-protected pseudoisocytosine and a silyl protected furanoid glycal. With this procedure the corresponding phosphoramidite building block is obtained in 5 steps and an overall yield of 28%.     

The use of barium salts of protected deoxyribonucleoside-3'' p-chlorophenyl phosphates for construction of oligonucleotides by the phosphotriester method: high-yield synthesis of dinucleotide blocks.

A new experimental approach to the synthesis of polydeoxyribonucleotides via the phosphotriester method involves construction of oligonucleotide blocks by direct use of the easily prepared barium salts of O5',N-protected deoxyribonucleoside-3' p-chlorophenyl phosphates as the key monomers in condensation reactions. The procedure has been demonstrated by the rapid synthesis in high yield and purity of all sixteen fuly protected dinucleotides (Formula: see text) (where dN' = dT, dbzC, dbzA, or dibG; (Formula: see text) This set of molecules constitutes a "syllabary" for the preparation of defined sequence oligonucleotides.     

Determination of the availability of carbodiimide-activated N-protected amino acids in solid phase peptide synthesis

A new method is described for the determination of the availability of carbodiimide-activated N-protected amino acids in solid phase peptide synthesis. The method involves the addition of a second nucleophile to a solid phase coupling reaction at different time intervals and measuring the amount of activated amino acid intercepted. Using the DCCI-mediated coupling reaction of Boc-Ala-OH and H-Gly-O-resin with H-Gly-O-tBu as the second nucleophile, it was determined that $\text{ca}$. 61% of the theoretical maximum amount of activated Boc-Ala-OH was available after 8 hr of reaction.     

Derivatives of Aminoquinones with N-protected Amino Acids

The synthesis of derivatives of aminoquinones with N-protected amino acids is reported here. 2-Amino-1,4-benzoquinone and 2-amino-1,4-naphthoquinone, prepared by the azide method in yields of 60 and 95% respectively, were coupled with N-Boc-protected amino acids including glycine, serine, proline and tyrosine, to give the correspondening derivatives. N,N'-Diisopropylcarbodiimide/1-hydroxybenzotriazole or N,N'-dicyclohexylcarbodiimide/HOBt used as coupling reagents provided the expected products in satisfactory yields and purities as supported by TLC, HPLC and spectral analysis.     

Resolution and absolute configuration of some α-aminoacetals: en route to enantiopure N-protected α-aminoaldehydes

The first successful resolution of rac-α-aminoacetals via diastereoisomeric salt formation with optically pure N-protected aminoacids is reported. The absolute configuration assignment of α-aminoacetal enantiomers is performed by an entirely non-racemizing chemical correlation method involving N-protection and a new efficient hydrolysis step followed by a reduction of the resulting N-protected α-aminoaldehyde intermediates. A racemization method of optically enriched α-aminoacetals is exemplified to allow valorisation of both enantiomers.     

SYNTHESIS OF RACEMIC AND ENANTIOMERIC 3-PYRROLIDINYL DERIVATIVES OF PURINE AND PYRIMIDINE NUCLEOBASES

The present work relates to the synthesis of pyrrolidine nucleoside analogs. Starting from malic acid, we have elaborated a high-yield synthesis of racemic and enantiomeric N-protected 3-pyrrolidinols and their O-mesyl derivatives as key compounds for alkylations of purine and pyrimidine nucleobases. On varying base and solvent, we have found conditions providing both satisfactory N-/O-regioisomeric ratio and acceptable yield for pyrimidine compounds.     

Synthesis of racemic and enantiomeric 3-pyrrolidinyl derivatives of purine and pyrimidine nucleobases

The present work relates to the synthesis of pyrrolidine nucleoside analogs. Starting from malic acid, we have elaborated a high-yield synthesis of racemic and enantiomeric N-protected 3-pyrrolidinols and their O-mesyl derivatives as key compounds for alkylations of purine and pyrimidine nucleobases. On varying base and solvent, we have found conditions providing both satisfactory N-/O-regioisomeric ratio and acceptable yield for pyrimidine compounds.     

Process design for enzymatic peptide synthesis in near-anhydrous organic media

This work is a case study on a process design for enzymatic peptide synthesis, which is based on and inspired by previously established data about the Alcalase-catalyzed coupling of an amino acid amide and a chemically synthesized activated N-protected amino acid carbamoylmethyl ester in near-anhydrous tetrahydrofuran. The choices with regard to Alcalase formulation, the type of reactor, method of controlling the water content, and whether or not to recycle the enzyme, are discussed. In addition, an estimate is given for the reactor size, volumes of solvent, amount of substrate, enzyme and molecular sieves, needed in order to meet a specific demand for peptides. We believe that this case study gives a good indication of the various choices that have to be made when designing a process for enzymatic peptide synthesis and the implications of these choices.     

Derivatives of Aminoquinones with N-protected Amino Acids

Summary The synthesis of derivatives of aminoquinones with N-protected amino acids is reported here. 2-Amino-1,4-benzoquinone and 2-amino-1,4-naphthoquinone, prepared by the azide method in yields of 60 and 95% respectively, were coupled with N-Boc-protected amino acids including glycine, serine, proline and tyrosine, to give the correspondening derivatives.N, N′-Diisopropylcarbodiimide/1-hydroxybenzotriazole orN, N′-dicyclohexylcarbodiimide/HOBt used as coupling reagents provided the expected products in satisfactory yields and purities as supported by TLC, HPLC and spectral analysis.     

Synthesis of the rac-6-hydroxy-3-methoxycyclohex-2-enone and resolution through recrystallization of its diastereomeric N-tosyl-(S)-proline esters

The synthesis and resolution of rac-6-hydroxy-3-methoxycyclohex-2-enone, by fractional crystallization of diastereomeric esters of N-protected (S)-proline was shown to be an effective method for preparation of both pure diastereomers (>95% d.e., according to (1)H NMR data). The absolute configuration of the asymmetric center in cyclohexene ring was determined based on the inversed octant rule for the sign of circular dichroism for these cyclohexenones (n-pi*-transition band at approximately 300 nm) and further substantiated by chemical conversion of the (-)-(6R,2'S)-diastereomer into the known (+)-(R)-4-hydroxycyclohex-2-enone. Copyright 2000 Wiley-Liss, Inc.     

Investigation of the effect of freezing on protease-catalyzed peptide synthesis using cryoprotectants and frozen organic solvent

In order to investigate the effect of freezing on aqueous protease-catalyzed peptide synthesis systems, the influence of polyethylene glycols as cryoprotecting substances on alpha-chymotrypsin-catalyzed coupling of a N-protected acyl donor ester and various nucleophilic amino components was studied. Changes in S'-specificity of alpha-chymotrypsin in frozen aqueous systems were suppressed by polyethylene glycols even at concentrations below 1% (w/v). Furthermore, the influence of freeze-concentration in organic solvents on protease-catalyzed peptide synthesis was investigated for the first time. In frozen tert-butanol, alpha-chymotrypsin-catalyzed peptide synthesis took advantage from freeze-concentration, but in contrast to frozen aqueous systems, no changes in S'-specificity of the biocatalyst were observed. The results suggest that freeze-concentration is not the only cause of freezing-induced yield improvement in aqueous peptide synthesis systems, but interactions between enzyme and ice structures strongly contribute to the observed effects.     

A convenient one-pot synthesis of asymmetric 1,3,5-triazine-2,4,6-triones and its application towards a novel class of gonadotropin-releasing hormone receptor antagonists

A convenient one-pot synthetic route was developed for the preparation of asymmetric 1,3-dialkyl-1,3,5-triazine-2,4,6-triones from readily available alkyl- or aryl-isocyanates, primary amines and N-chlorocarbonyl isocyanate in excellent yields. Subsequent alkylation with N-protected amino alcohols afforded the desired 1,3,5-triazine-2,4,6-triones in good yields. This methodology was applied to the synthesis of a chemical library acting as antagonists of the hGnRH receptor.     

Formation of peptide bonds by carboxypeptidase c from orange leaves.

Carboxypeptidase c partially purified from orange leaves was studied as a catalyst for enzymatic peptide synthesis. Various N-protected ester- and nucleophile compounds were evaluated in order to determine the substrate specificity. For further characterization of the synthetic reaction, optimum pH and the influence of the N-terminal protecting group were studied. Kinetic investigations revealed considerable differences in Km and Vmax for the nucleophile when the N-terminal protecting group of the substrate was varied.     

Improved synthesis of oligodeoxyribonucleotide using 3-methoxy-4-phenoxybenzoyl group for amino protection.

3-Methoxy-4-phenoxybenzoyl group has been used for the protection of exocyclic amino group of nucleosides. In case of 2'-deoxycytidine it has been found to be highly selective under controlled conditions. The N-protected derivatives of 2'-deoxyadenosine and 2'-deoxyguanosine have been found to be sufficiently stable towards acids minimising depurination under conditions of synthesis of oligodeoxyribonucleotide on solid support via phosphotriester approach. The high lipophilicity of the group and milder deprotection conditions are additional advantages.