Facile synthesis of Nα‐protected‐l‐α,γ‐diaminobutyric acids mediated by polymer‐supported hypervalent iodine reagent in water

Abstract: Hofmann rearrangement of N^α‐Boc‐l ‐Gln‐OH mediated by a polymer‐supported hypervalent iodine reagent poly[(4‐diacetoxyiodo)styrene] (PSDIB) in water afforded N^α‐Boc‐l ‐α,γ‐diaminobutyric acid (Boc‐Dab‐OH, 1 ) in 87% yield. N^α‐Z‐derivative (Z‐Dab‐OH, 2 ) was prepared with PSDIB in 83% yield. Since the reaction of N^α‐Fmoc‐Gln‐OH by this procedure did not proceed because of the insolubility of Fmoc‐Gln‐OH in aqueous media, we synthesized Fmoc‐Dab(Boc)‐OH ( 5 ) from 2 in 54% yield. Polymyxin B heptapeptide (PMBH) which contains four Dab residues was successfully synthesized in a solution‐phase synthesis.     

Microwave‐accelerated synthesis of psychoactive deuterated N,N‐dialkylated‐[α,α,β,β‐d4]‐tryptamines

A large number of N,N‐dialkylated tryptamines are known to induce psychoactive effects in humans. This has resulted in their increased attention within clinical and forensic communities. Deuterated tryptamines are ideal for use as internal standards during MS bioanalysis or of use in biochemical NMR studies. The present study reports on a microwave‐enhanced synthesis of 22 N,N‐dialkylated‐[α,α,β,β‐d4]‐tryptamines via the reduction with lithium aluminium deuteride of glyoxalylamide precursors obtained by the procedure of Speeter and Anthony. Syntheses were carried out using a single‐mode system under elevated pressure conditions where anhydrous tetrahydrofuran was used as the solvent at 150°C. Good yields were obtained within 5 min. Copyright © 2008 John Wiley & Sons, Ltd.     

Entrapping unusual folding characteristics of the β‐Ala residues in a model peptide: Boc‐β‐Ala‐Aib‐β‐Ala‐NHCH3

Abstract: Crystal structure analysis of a model peptide: Boc‐β‐Ala‐Aib‐β‐Ala‐NHCH₃ (β‐Ala: 3‐amino propionic acid; Aib: α‐aminoisobutyric acid) revealed distinct conformational preferences for folded [φ≈136°, µ ≈ ?62°, ψ ≈100°] and semifolded [φ ≈ 83°, µ ≈ ?177°, ψ ≈ ?117°] structures of the N‐ and C‐terminus β‐Ala residues, respectively. The overall folded conformation is stabilized by unusual N_i···H‐N_i+1 and nonconventional C–H···O intramolecular hydrogen bonding interactions.     

Synthesis of N‐(2‐chloro‐3,4‐dimethoxybenzylideneamino)guanidinium acetate [α‐14C]

¹⁴C‐Labelled N‐(2‐chloro‐3,4‐dimethoxybenzylideneamino)guanidinium acetate has been synthesized as a part of a four‐step procedure which involved decarboxylation of 2‐chloro‐3,4‐dimethoxybenzoic acid by Pb(OAc)₄ to give 2‐chloro‐3,4‐dimethoxy‐1‐iodobenzene, followed by a selective lithiation at the iodine position and electrophilic substitution with N,N‐dimethylformamide [α‐¹⁴C] and final reaction with aminoguanidine bicarbonate. The specific activity was 59 mCi/mmol and the overall yield 49%. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of deoxyadenosine‐5′‐(35S)‐thiomonophosphate [dAMP(35S)] of high specific activity – a key intermediate for the synthesis of Sp‐deoxyadenosine‐5′‐(alpha;‐35S)‐thiotriphosphate [Sp‐dATP (α‐35S)]

Unprotected deoxyadenosine 1 was treated with an excess of phosphorus acid and stoichiometric proportions of N, N′‐di‐p‐tolylcarbodiimide in anhydrous pyridine to give deoxyadenosine‐5′‐monophosphite 2 . The latter was activated with trimethylsilyl chloride followed by sulphurisation with elemental ³⁵S (specific activity>1000 Ci/mmol) in toluene solution to give deoxyadenosine‐5′‐(³⁵S)‐thiomonophosphate [dAMP(³⁵S)] 3 . Enzymatic conversion of deoxyadenosine‐5′‐(³⁵S)‐thiomonophosphate to Sp‐deoxyadenosine‐5′‐(α‐³⁵S)‐thiotriphosphate [Sp‐dATP (α‐³⁵S)] 5 was carried out following a standard reaction protocol. Copyright © 2001 John Wiley & Sons, Ltd.     

Stereoselective Synthesis and Antiviral Activity of (1E,2Z,3E)‐1‐(Piperidin‐1‐yl)‐1‐(arylhydrazono)‐2‐[(benzoyl/benzothiazol‐ 2‐oyl)hydrazono]‐4‐(aryl1)but‐3‐enes

The reaction of benzoyl hydrazine 1a or benzothiazole‐2‐carbohydrazide 1b with 2‐oxo‐N‐arylpropanehydrazonoyl chlorides 2a–d yielded (1Z,2E)‐2‐[(benzoyl/benzothiazol‐2‐oyl)hydrazono]‐N‐(aryl)propanehydrazonoyl chlorides 3a–e . The reaction of 3a–c with sodium benzenesulphinate furnished sulphones 5a–c while the reaction of 5d , e with hydroxyl amine afforded hydroxomoyl derivatives 6a , b . The one‐pot sterioselective reaction of N‐(aryl)propanehydrazonoyl chlorides 3 with certain aromatic aldehydes in the presence of piperidine resulted in the formation of (1E,2Z,3E)‐1‐(piperidin‐1‐yl)‐1‐(arylhydrazono)‐2‐[(benzoyl/benzothiazol‐2‐oyl)hydrazono]‐4‐(aryl¹)‐but‐3‐enes 7a–g . X‐ray analysis of piperidinyl amidrazone 7g showed a conversion of its geometrical structure with respect to that of compound 3 and confirmed the stereoselectivity of the latter reaction. The piperidinyl amidrazones 7a–g possessed a significant antiviral activity against herpes simplex viruses (HSV‐1). Compound 7d reduced the number of viral plaques of herpes simplex type‐1 (HSV‐1) by 67%, with respect to the effect of reference drug Aphidicolin.     

Synthesis of N‐(3‐[18F]Fluoropropyl)‐2β‐carbomethoxy‐3β‐(4‐iodophenyl)nortropane ([18F]FP‐β‐CIT)

N‐(3‐[¹⁸F]fluoropropyl)‐2β‐carbomethoxy‐3β‐(4‐iodophenyl)nortropane ([¹⁸F]FP‐β‐CIT) was synthesized in a two‐step reaction sequence. In the first reaction, 1‐bromo‐3‐(nitrobenzene‐4‐sulfonyloxy)‐propane was fluorinated with no‐carrier‐added fluorine‐18. The resulting product, 1‐bromo‐3‐[¹⁸F]‐fluoropropane, was distilled into a cooled reaction vessel containing 2β‐carbomethoxy‐3β‐(4‐iodophenyl)‐nortropane, diisopropylethylamine and potassium iodide. After 30 min, the reaction mixture was subjected to a preparative HPLC purification. The product, [¹⁸F]FP‐β‐CIT, was isolated from the HPLC eluent with solid‐phase extraction and formulated to yield an isotonic, pyrogen‐free and sterile solution of [¹⁸F]FP‐β‐CIT. The overall decay‐corrected radiochemical yield was 25 ± 5%. Radiochemical purity was > 98% and the specific activity was 94 ± 50 GBq/µmol at the end of synthesis. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of N,N‐diethyl‐4‐[phenyl‐(piperidin‐4‐ylidene)methyl]‐[carboxy‐14C]benzamide,a potent δ opioid receptor agonist

The synthesis of carbon‐14 labelled N,N‐diethyl‐4‐[phenyl‐(piperidin‐4‐ylidene)methyl]‐benzamide is described. The radioisotope is introduced via an aryllithium reaction with ¹⁴CO₂ to form the labelled acid, which is subsequently transformed into the amide. Copyright © 2002 John Wiley & Sons, Ltd.     

From β‐N‐tert‐butyloxycarbonyl N‐carboxyanhydrides to β‐aminoacid derivatives

Abstract: β‐N‐tert‐butyloxycarbonyl‐N‐carboxyanhydrides are very reactive β‐amino acid derivatives. They react cleanly and smoothly with different nucleophiles like aminoesters, enolates, N‐methyl‐d ‐glucamine, amidoximes to afford in good to excellent yields peptides, β‐amino ketocompounds, β‐aminosugars and functionalized disubstituted 1,2,4‐oxadiazoles.     

Synthesis of [guanido‐13C]‐γ‐hydroxyarginine

This report describes an efficient method of synthesizing [guanido‐¹³C]‐γ‐hydroxyarginine HCl salt. Iodolactonization of N‐Boc‐protected allylglycine mainly provided the cis iodo compound 2. This was converted to an amine through azide 4. The amine 5 was reacted with N‐Boc‐protected [¹³C]thiourea to afford N‐Boc‐protected [¹³C]guanidine 6, which underwent base catalyzed ring opening. Removal of the N‐Boc group afforded [guanido‐¹³C]‐γ‐hydroxyarginine HCl salt 7 giving a 30% overall yield of the final product from N‐Boc protected allylglycine 1 in five steps. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and radiolabelling of Re(CO)3‐β‐elemene derivatives as potential therapeutic radiopharmaceuticals

β‐Elemene, (1S, 2S, 4R)‐(?)‐(1‐methy‐1‐vinyl‐2,4‐diisopropenyl cyclohexane) is an anticancer agent from the Traditional Chinese Herb Medicinal. Three novel Re(CO)₃‐β‐elemene derivatives including their radioactive conjugates containing N,N,N tridentate ligands and tricarbonyl rhenium (complex 12, 13, 14) were synthesized. Their structures were characterized by infrared (IR), ¹H‐NMR and HRMS. Good radioactive yield (above 90%) and radioactive chemical purity with Re‐188 (above 95%) were obtained for all of the three derivatives (complex 15, 16, 17). The antiproliferative activity of non‐radioactive β‐elemene‐Re(CO)₃ derivatives on Lewis lung cancer cells and HeLa cell lines were evaluated by WST‐1 methods. The result shows substantial decrease in IC₅₀ values compared with the parent compound β‐elemene. The synthesis and radiosynthesis of β‐elemene tricarbonyl rhenium conjugates provide the possibility to find a new kind of potential radiopharmaceuticals on β‐elemene. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of [15N4] purine labeled cytokinin glycosides derived from zeatins and topolins with 9‐β‐d, 7‐β‐d‐glucopyranosyl,or 9‐β‐d‐ribofuranosyl group

Synthesis of [¹⁵N₄] purine labeled cytokinine glycosides derived from zeatins and topolins containing a 9‐β‐d , 7‐β‐d ‐glucopyranosyl, or 9‐β‐d ‐ribofuranosyl group is described. These N⁶‐substituted adenine derivatives are intended as internal analytic standards for phytohormone analysis. All labeled compounds were prepared from 6‐chloro[¹⁵N₄]purine ( 1 ). The equilibrium reaction of 1 with acetobromo‐α‐d ‐glucose gave isomeric 7‐β‐d ( 3 ) and 9‐β‐d ( 4 ) chloro glucosyl precursors, which were treated with the corresponding amines to get desired labeled cytokinin 7‐β‐d ( 6 ) and 9‐β‐d ( 5 ) glucopyranosides. Cytokinins containing 9‐β‐d ‐ribofuranosyl group ( 8 ) were obtained by direct enzymatic transglycosylation reaction of cytokinins ( 7 ) prepared from 6‐chloro[¹⁵N₄] purine ( 1 ).     

Synthesis of 3,7,8‐15N3‐N1‐(β‐D‐erythro‐pentofuranosyl)‐5‐guanidinohydantoin

3,7,8‐¹⁵N₃‐N¹‐(β‐D‐erythro‐pentofuranosyl)‐5‐guanidinohydantoin was synthesized from the oxidation of 1,7,NH₂‐¹⁵N₃‐8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine with 2 equivalents of Ir(IV) in pH 4.5 potassium phosphate buffer. The synthesis of 1,7,NH₂‐¹⁵N₃‐8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine started with bromination of 1,7,NH₂‐¹⁵N₃‐2′‐deoxyguanosine. The resulting 1,7,NH₂‐¹⁵N₃‐8‐bromo‐7,8‐dihydro‐2′‐deoxyguanosine reacted with sodium benzyloxide to afford 1,7,NH₂‐¹⁵N₃‐8‐benzyloxy‐7,8‐dihydro‐2′‐deoxyguanosine. Subsequent catalytic transfer hydrogenation of 1,7,NH₂‐¹⁵N₃‐8‐benzyloxy‐7,8‐dihydro‐2′‐deoxyguanosine with cyclohexene and 10% Pd/C yielded 1,7,NH₂‐¹⁵N₃‐8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine. Purification of 3,7,8‐¹⁵N₃‐N¹‐(β‐D‐erythro‐pentofuranosyl)‐5‐guanidinohydantoin was first carried out on a C18 column and the product was further purified on a graphite column. ESI‐MS was used to confirm the identity and to determine the isotopic purity of all the labeled compounds. The isotopic purity of 3,7,8‐¹⁵N₃‐N¹‐(β‐D‐erythro‐pentofuranosyl)‐5‐guanidinohydantoin was 99.4 atom% based on LC‐MS measurements. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis and characterization of human α‐defensins 4‐6

Abstract: Human α‐defensins are small, Cys‐rich, cationic proteins expressed predominantly in neutrophils and intestinal epithelia. They play important roles in innate and adaptive immunity against infection. Progress in studying these molecules can be accelerated by access to large quantities of high‐quality materials, which have been obtained mainly from natural sources. Here, we report total synthesis of human α‐defensins 4, 5, and 6, also known as HNP4, HD5, and HD6, using the optimized N,N‐diisopropylethylamine (DIEA) in situ neutralization/2‐(1 H‐benzotriazolyl)‐1,1,3,3‐tetramethyluroniumhexafluorophosphate (HBTU) activation protocol for solid‐phase Boc chemistry. Oxidative folding/disulfide formation was achieved directly using crude peptides, resulting in an overall synthetic yield of 10–16% with high purity. Antimicrobial activity assays were performed with Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213, using colony‐counting methods, and the results demonstrated differential activity against these strains. Our report describes a highly efficient synthetic approach that enables thorough structural and functional studies of these three important immunologic molecules.     

Efficient O‐ and N‐(β‐fluoroethylation)s with NCA [18F]β‐fluoroethyl tosylate under microwave‐enhanced conditions

Reactions of no‐carrier‐added (NCA) [¹⁸F]β‐fluoroethyl tosylate with amine, phenol or carboxylic acid to form the corresponding [¹⁸F]N‐(β‐fluoroethyl)amine, [¹⁸F]β‐fluoroethyl ether or [¹⁸F]β‐fluoroethyl ester, were found to be rapid (2–10 min) and efficient (51–89% conversion) under microwave‐enhanced conditions. These conditions allow reactants to be heated rapidly to 150°C in a low boiling point solvent, such as acetonitrile, and avoid the need to use high boiling point solvents, such as DMSO and DMF, to promote reaction. The microwave‐enhanced reactions gave about 20% greater radiochemical yields than thermal reactions performed at similar temperatures and over similar reaction times. With a bi‐functional molecule, such as DL‐pipecolinic acid, [¹⁸F]β‐fluoroethyl tosylate reacts exclusively with the amino group. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of [N‐methyl‐11C]‐3‐[(6‐dimethylamino)pyridin‐3‐yl]‐2,5‐dimethyl‐N,N‐dipropylpyrazolo[1,5‐a]pyrimidine‐7‐amine: A potential PET ligand for in vivo imaging of CRF1 receptors

A convenient synthesis of [N‐methyl‐¹¹C]‐3‐[(6‐dimethylamino)pyridin‐3‐yl]‐2,5‐dimethyl‐N,N‐dipropylpyrazolo[1,5‐a]pyrimidine‐7‐amine (R121920), a highly selective CRF₁ antagonist has been developed as a potential PET ligand. 3 ‐ [(6 ‐ methylamino)pyridin ‐ 3 ‐ yl]‐2,5‐dimethyl‐N,N‐dipropylpyrazolo [1,5‐a]pyrimidine‐7‐amine ( 7 ), the precursor for radiolabelling was synthesized through a novel palladium catalyzed Suzuki coupling of aryl bromide 5 with heteroaryl boronate ester 4 . The requisite boronate ester 4 was synthesized in four steps from 2‐amino‐4‐bromopyridine in 50% overall yield. Although the synthesis of cold R121920 proceeded in 93% yield by sodium hexamethyl‐disilazide (NaHMDS) mediated N‐methylation of the desmethylamine 7 at ?78°C, the attempted radiosynthesis under various conditions using conventional bases were not successful. However, the radiolabeling of [¹¹C]R121920 was successfully carried out with [¹¹C]MeOTf in acetone at ?20°C in the absence of added basic reagents. The radiotracer was purified by RP‐HPLC followed by RP‐solid phase extraction. The yield of the reaction was 5% (at EOB) and the specific activity was >1000 Ci/mmol (at EOB) with a radiochemical purity >99%. Copyright © 2003 John Wiley & Sons, Ltd.     

Chemical synthesis and receptor binding of catfish somatostatin: a disulfide‐bridged β‐d‐Galp‐(1→3)‐α‐d‐GalpNAc O‐glycopeptide*

Abstract: The glycopeptide hormone catfish somatostatin (somatostatin‐22) has the amino acid sequence H‐Asp‐Asn‐Thr‐Val‐Thr‐Ser‐Lys‐Pro‐Leu‐Asn‐Cys‐Met‐Asn‐Tyr‐Phe‐Trp‐Lys‐Ser‐Arg‐Thr‐Ala‐Cys‐OH; it includes a cyclic disulfide connecting the two Cys residues, and the major naturally occurring glycoform contains d ‐GalNAc and d ‐Gal O‐glycosidically linked to Thr⁵. The linear sequence was assembled smoothly starting with an Fmoc‐Cys(Trt)‐PAC‐PEG‐PS support, using stepwise Fmoc solid‐phase chemistry. In addition to the nonglycosylated peptide, two glycosylated forms of somatostatin‐22 were accessed by incorporating as building blocks, respectively, N^α‐Fmoc‐Thr(Ac₃‐α‐D‐GalNAc)‐OH and N^α‐Fmoc‐Thr(Ac₄‐β‐D‐Gal‐(1→3)‐Ac₂‐α‐D‐GalNAc)‐OH. Acidolytic deprotection/cleavage of these peptidyl‐resins with trifluoroacetic acid/scavenger cocktails gave the corresponding acetyl‐protected glycopeptides with free sulfhydryl functions. Deacetylation, by methanolysis in the presence of catalytic sodium methoxide, was followed by mild oxidation at pH 7, mediated by N^α‐dithiasuccinoyl (Dts)‐glycine, to provide the desired monomeric cyclic disulfides. The purified peptides were tested for binding affinities to a panel of cloned human somatostatin receptor subtypes; in several cases, presence of the disaccharide moiety resulted in 2‐fold tighter binding.     

Synthesis,crystal structure and molecular conformation of Nα‐Boc‐l‐leucyl‐(Z)‐β‐(3‐pyridyl)‐α,β‐ dehydroalanyl‐l‐leucine methyl ester*

Abstract: A protected tridehydropeptide containing (Z)‐β‐(3‐pyridyl)‐α,β‐dehydroalanine (Δ^Z3Pal) residue, Boc‐Leu‐Δ^Z3Pal‐Leu‐OMe ( 1 ), was synthesized via Erlenmeyer azlactone method. X‐ray crystallographic analysis revealed that the peptide 1 adopts an extended conformation, which is similar to that of a Δ^ZPhe analog, Boc‐Leu‐Δ^ZPhe‐Leu‐OMe ( 2 ).     

The catalase activity of Nα‐acetyl‐microperoxidase‐8

Abstract: N ^α ‐Acetylated microperoxidase‐8 (Ac‐MP‐8) is a water soluble, ferric heme model for peroxidases. We report here that Ac‐MP‐8 catalyzes catalase‐type reaction in addition to peroxidase‐type and cytochrome P450‐type reactions. The catalase activity of Ac‐MP‐8 was determined by the Clark oxygen electrode, which measures the production of oxygen in solution. The K_m and k_cat of the decomposition of hydrogen peroxide (H₂O₂) catalyzed by Ac‐MP‐8 are 40.9 mm and 4.1 per s, respectively. The specificity constant (k_cat/K_m) of Ac‐MP‐8 in catalase‐type reaction of H₂O₂ is 100.2,/m /s, which is 5‐ to 12‐ and 50‐ to 100‐fold less than those of MPs in cytochrome P450‐type reaction of aniline/H₂O₂ and peroxidase‐type reaction of o‐methoxyphenol/H₂O₂, respectively. These results indicate that Ac‐MP‐8 can catalyze three different types of reactions, and the relative catalytic specificities of Ac‐MP‐8 with a histidyl ligand exhibit the following orders: peroxidase‐type > cytochrome P450‐type > catalase‐type reactions. Comparisons of the enzyme activities of Ac‐MP‐8 suggest that the fifth ligands of hemoproteins influence the ratio of the three types of reactions.     

In vitro Metabolism of Two Heterocyclic Amines, 2‐Amino‐9H‐pyrido[2,3‐b]indole (AαC) and 2‐Amino‐3‐methyl‐9H‐pyrido[2,3‐b]indole (MeAαC) in Human and Rat Hepatic Microsomes

Abstract: 2‐Amino‐9H‐pyrido[2,3‐b]indole (AαC) and 2‐amino‐3‐methyl‐9H‐pyrido[2,3‐b]indole (MeAαC) are two mutagenic and carcinogenic heterocyclic amines formed during ordinary cooking. In this study, we have investigated the in vitro metabolism of tritium‐labelled AαC and MeAαC in hepatic microsomes from human pools, rats induced with polychlorinated biphenyl (PCB) (Aroclor 1254) and control rats. The microsomes were incubated with AαC and MeAαC and the detoxified and activated metabolites of AαC and MeAαC were separated and characterised by HPLC‐MS. AαC is metabolised to two major and three minor detoxified metabolites, while MeAαC is metabolised to three major and one minor detoxified metabolites. Some AαC and MeAαC are activated by oxidation to the reactive metabolites N²‐OH‐AαC and N²‐OH‐MeAαC, respectively. These reactive N²‐OH‐metabolites react partially in the incubation system with formation of protein adducts, dimers and the parent compound by reduction of the N²‐OH‐metabolites. The distribution between the detoxified and activated metabolites in the different types of hepatic microsomes showed same pattern for both AαC and MeAαC. In PCB‐induced rat microsomes, the major part of the metabolites are detoxified, only a little amount is activated. In control rat microsomes there is a fifty‐fifty distribution between detoxification and activation, while the major part of the metabolites from the human microsomes are activated and reacts to form dimers and protein adducts. These data show that, in human hepatic microsomes compared to rat hepatic microsomes, a major part of AαC and MeAαC are metabolically activated to the reactive N²‐OH‐AαC and N²‐OH‐MeAαC.