5-Isothiazolidinonyl and 5-isoxazolidinonyl radicals : Approaches to the biogenetic-type synthesis of β-lactams

A possible mechanism for penicillin biosynthesis involves the rearrangement of a 5-isothiazolidinonyl radical (6) to a β-lactam. However, generation of the model radicals (13 and 20) did not lead to β-lactams. The analogous reaction of a 5-isoxazolidinonyl radical is the basis for a potential synthesis of clavulanic acid, but again the rearrangement was not observed in the model radical (24).     

Total synthesis of monocyclic β-lactam antibiotics,nocardicin A and D

The total synthesis of monocyclic β-lactam antibiotics, nocardicins A (1a) and D (1d), is described. 3-Aminonocardicinic acid (3-ANA, 2) was synthesized from p-hydroxyphenylglycine via an acid chloride-imine cyloaddition reaction. The side chain amino acid 13 was prepared via a key step of condensation of p-hydroxyacetophenone and α-phthalimidobutyrolactone. Acylation of 3-ANA with 13 gave nocardicin D, from which nocardicin A was obtained by oximation.     

The synthesis of αβ-unsaturated ketones from β-silylenones and β-silylynones

Conjugate addition, followed by alkylation, bromination and desilyl-bromination make the β-silylketone (4) an a³d³-synthon (5) and the β-silylynone (6) a 2a³d³-synthon (7).     

Synthesis of 4-aryl-substituted β-lactam enantiomers by enzyme-catalyzed kinetic resolution

Enantiopure 4-phenyl- and 4-(p-tolyl)-2-azetidinones 3a, 3b, 4a and 4b (with e.e.s of ≥96%) were prepared through lipase-catalyzed asymmetric butyrylation of the primary OH group of N-hydroxymethylated β-lactams (±)-5 and (±)-6 at the (R)-stereogenic centre or by lipase-catalyzed asymmetric debutyrylation of O-butyryloxymethyl-2-azetidinones (±)-7 and (±)-8 at the (R)-stereogenic centre. The ring-opening of lactams 5a, 5b, 6b and 8a with HCl/EtOH afforded the corresponding β-amino ester enantiomers 9a, 9b, 10a and 10b with e.e.s of ≥92%.     

Photochemistry of β,γ-enones-VIII: On the remarkable photostability of some β,γ.β',γ'-dienones and the 1,3-acyl shift photoreactivity of two β,γ.γ',δ'-dienones

The direct irradiation of the β,γ.β',γ'-dienones 1–5 and the β,γ.γ',δ'-dienones (E)-6a, (E)-7a and 8a at λ 300 nm has been studied. The β,γ.β,γ'-dienones 1–5 are remarkable photostable for λ ? 300 nm, even upon prolonged irradiation, in contrast to simple β,γ-enones which upon irradiation exhibit α-cleavage, γ-hydrogen abstraction, (E)-(Z) isomerization and oxetane formation. The observed photostability of the β,γ.β',γ'-dienones is rationalized in terms of a rapid radiationless decay of the excited singlet state, enhanced by CT-interaction between the carbonyl ¹(n-π*) state and the homoconjugated 1,4-diene moiety, which precludes fluorescence, photochemical reactions and intersystem crossing (ISC).The β,γ.γ',δ'-dienones (E)-(6a), (E)-7a and 8a exhibit only a 1,3-acyl shift (1,3-AS) without (E)-(Z) isomerization of the alkenyl moiety, to yield (E)-6b, (E)-7b and 8b. It is concluded that the 1,3-AS proceeds from the ¹(n-π*) state with a rate which is very large relative to the rate of ISC to the ³(n-π*) state, thus precluding any internal triplet energy transfer (1TET) from the ³(n-π*) to the ³(π-π*) state which would manifest itself by (E)-(Z) isomerization.     

Synthesis,antimicrobial and cytotoxic activity of novel azetidine-2-one derivatives of 1H-benzimidazole

A series of 1-methyl-N-[(substituted-phenylmethylidene)-1H-benzimidazol-2-amines (4a–4g) were prepared via the formation of 1-methyl-1H-benzimidazol-2-amine (3), which was prepared by the cycloaddition of o-phenylenediamine (1) with cyanogen bromide in the presence of aqueous base followed by N-methylation with methyl iodide in the presence of anhydrous potassium carbonate in dry acetonitrile. Moreover, the four-membered β-lactam ring was introduced by the cycloaddition of 4a–4g and chloroacetyl chloride in the presence of triethylamine catalyst to give 3-chloro-1-(1-methyl-1H-benzimidazol-2-yl)-(4′-substituted)-phenylazetidin-2-one 5a–5g. A total of 14 compounds were synthesized and characterized by IR, ¹H NMR, ¹³C NMR and Mass spectral technique, in addition they were evaluated for anti-bacterial and cytotoxic properties. Among the chemicals tested 4a, 4b, 5a, 5b, 5g exhibited good antibacterial activity and 5f, 5g shown good cytotoxic activity in vitro.     

On Triazoles. XIII. The reaction of 5-benzalimino-1,2,4-triazoles with substituted acetyl chlorides

The reaction of Schiff bases prepared from 1- and 2-substituted-5-amino-1,2,4-triazoles with phenoxyacetyl chlorides in the presence of triethylamine and a mixture of phosphorus oxychloride and dichloroacetic acid in dimethylformamide to yield β-lactam 4 , a dihydro-1,2,4-triazolo[4,3-a]pyrimidine-5(1H)-one 5, a 1,2,4-triazolo[1,5-a]pyrimidin-5(3H)-one 9 and the corresponding 1,2,4-triazolo[4,3-a]pyrimidine-5(1H)-one 10 derivatives was studied.     

C-3 β-lactam carbocation equivalents: versatile synthons for C-3 substituted β-lactams

An efficient and operationally simple strategy for the synthesis of differently C-3 monosubstituted (9) and disubstituted (10) monocyclic β-lactams is described. This involves reaction of β-lactam carbocation equivalents (8) with an active aromatic, aliphatic and heterocyclic substrates in the presence of a Lewis acid.     

Porcine pancreatic lipase mediated regio- and stereoselective hydrolysis: chemoenzymatic synthesis of (2S,3S)-2-amino-3,4-dihydroxybutyric acid

Porcine pancreatic lipase was used in the chemoenzymatic hydrolysis of 2-azido-3-hydroxy-4-methylcarbonyloxybutyl acetate. The reaction occurred with high regio- and stereoselectivity to give enantiomerically pure (2S,3R)-3-azido-2,4-dihydroxy butyl acetate 5 (e.e. >99%) which was easily converted to (2S,3S)-2-amino-3,4-dihydroxybutyric acid 1, an important synthetic intermediate in the synthesis of β-lactam antibiotics and phytosiderophores.     

Preparation of (1R,8S)- and (1S,8R)-9-azabicyclo[6.2.0]dec-4-en-10-one: potential starting compounds for the synthesis of anatoxin-a

9-Azabicyclo[6.2.0]dec-4-en-10-one (±)-2, obtained from cyclooctadiene by addition of chlorosulfonyl isocyanate, was N-hydroxymethylated to (±)-3 and then resolved by lipase-catalysed asymmetric acylation of the primary OH group at the (S)-stereogenic centre. High enantioselectivity (E=94) was observed when lipase PS and vinyl butyrate were used in di-iso-propyl ether at −15°C, resulting in the enantiomerically enriched ester 3a and alcohol 3b (e.e. ≥92%). Treatment of 3a and 3b with NH₄OH/MeOH afforded the corresponding β-lactams (1R,8S)-2a and (1S,8R)-2b (e.e. ≥93%), potential starting compounds in anatoxin-a synthesis. The ring opening of lactams (±)-2, (±)-7, 3a and 3b, followed by reduction, resulted in racemic 4–6 and 8 and enantiomeric 4a, 4b, 5a and 5b eight-membered cyclic β-amino acid derivatives.     

Studies on the Suzuki reaction on methyl 1-(2-bromoaryl)-5-oxo-3-aryl/heteroaryl-pyrrolidin-2-carboxylate derivatives: synthesis of N-aryl modified monocyclic γ-lactam derivatives in search for newer antibacterial agents

A large number of novel N-aryl modified monocyclic γ-lactam derivatives have been prepared via Pd(0) catalyzed heteroarylation in the N-aryl part of (±) cis and (±) trans γ-lactam carboxylate derivatives 3(a–f) and 6(a–f), respectively, with furan-2-boronic acid and thiophen-2-boronic acid. (±) cis Methyl 1-(2-bromoaryl)-5-oxo-3-aryl/heteroarylpyrrolidin-2-carboxylate derivatives 3(a–f), were prepared in good yields from 1(a–f) via hydrolysis, stereoselective decarboxylation, followed by esterification. Corresponding trans isomers 6(a–f) were prepared by the standard method already reported by us.     

The stereoselective synthesis of γ-lactam derivatives through N(1)-C(4) one carbon ring expansion of β-lactam derivatives

The base induced ring opening of β-lactam derivatives, 3, 5, 7, 9, 11 with LDA gave γ-lactam derivatives, 4, 6, 8, 10, 12 stereoselectively. The γ-lactam derivatives were formed stereoselectively depending on C-3 substituent of β-lactam derivatives.     

Stereoselective syntheses of pinane-based 1,3-diamines and their application as chiral ligands in the enantioselective addition of diethylzinc to benzaldehyde

A library of 1,3-difunctionalized pinane derivatives was synthesized and applied as chiral catalysts in the addition of diethylzinc to benzaldehyde. The key intermediate β-lactam 2 was prepared regio- and stereoselectively from (?)-apopinene 1. The treatment of 2 with di-tert-butyl dicarbonate afforded N-Boc β-lactam 3, while acid-catalyzed ring opening of 2 resulted in amino acid 4. Nucleophilic ring opening of 3 with dimethylamine, followed by deprotection and benzylation, furnished β-amino amides 5, 8, and 11, which were transformed in two steps into the corresponding N-tosyldiamines 7, 10, and 13, respectively. Since the use of other amines, such as diethylamine, to study the influence of dialkyl substitution was unsuccessful, an alternative synthetic route was applied. Amidation of tosylated β-amino acid 14 furnished amides 15–25. Reduction of 15, 16, 19, 20, and 24 resulted in N-tosyl diamines 26–30. The β-amino amides and N-tosylated diamines were used as chiral ligands in the enantioselective alkylation of benzaldehyde with diethylzinc, resulting in (R)- and (S)-1-phenyl-1-propanol. The (R)-enantiomer was predominant except when 17, 22, 23, and 25 were used as ligands, in which case the opposite stereochemistry was observed. The best ee values (up to 83%) were obtained when 17, 20, 23, and 25 were used as catalysts.     

Cycloaddition reactions of 1,3-benzothiazines—I. : Reactions of 2-phenyl-4-H and 4-phenyl-2H-1,3-benzothiazine derivatives with substituted acetyl chlorides

6,7-Dimethoxy-2-phenyl-4$\text{H}$-1,3-benzothiazine (1) and 6,7-dimethoxy-4-phenyl-2$\text{H}$-1,3-benzothiazine (2) react with substituted acetyl chlorides to give linearly, and new angularly condensed β-lactam derivatives (4,5). Heating of the latter compounds with hydrogen chloride in anhydrous ethanol leads to the formation of the corresponding 4$\text{H}$- and 2$\text{H}$-1,3-benzothiazinium chloride, respectively. The configurations of these compounds (the mutual positions of the substituents relative to the β-lactam ring) were determined by ¹H and ¹³C studies, also making use of the aromatic solvent-induced shifts.     

Synthesis of new nanocopolymer containing β-lactams

Several new monocyclic β-lactam monomers bearing the NO₂ group 2a–g were synthesized via a [2 + 2] ketene–imine cycloaddition reaction (Staudinger reaction). Calculation of coupling constant of H-3 and H-4, and the X-ray crystallography of β-lactam 2e confirmed the cis stereochemistry of these β-lactams. Then aminophenyl β-lactams were synthesized by the reduction of NO₂ to NH₂ group in the presence of Raney Ni and hydrazine hydrate. Treatment of these aminophenyl β-lactams with acryloyl chloride and sodium bicarbonate (NaHCO₃), afforded the monomers bearing the NHCOCH=CH₂ group. These acrylated β-lactam monomers were dissolved in a warm mixture of butyl acrylate and styrene and then were converted to the corresponding polyacrylate nano β-lactams by emulsion polymerization in water. A unique feature of this methodology is the ability to incorporate water-insoluble compounds directly into the nanoparticle framework. Structures of the synthesized compounds were confirmed by physical and spectral analyses. Dynamic light scattering analysis and transmission electron microscopy of the final emulsions show that the nanoparticles were about 50–70 nm in diameter.     

A stereocontrolled formal total synthesis of (±)-thienamycin

The stereocontrolled synthesis of a key intermediate 20 for the preparation of (±)-thienamycin 1 is described. The key steps in the synthesis are the formation of the β-lactam ring by cyclization of the amide 5 via a complete S_N2 mechanism, and the stereospecific conversion of the azetidinone 5 to the amide (trans-11) which have the correct relative configurations at three contiguous chiral centres. The mechanism of the conversion of the azetidinone 16E to the N-free azetidinone 17 and the selenide compound 18 is presumed.     

Synthese von (5,10)-(7,8)-Bisepoxiden aus α- und β-4-Phenyl-1,2,4-triazolin-3,5-dion-Addukten von Vitamin D3 und Röntgenstrukturanalyse eines der Benzoylderivate

Oxidation of the α- and β-4-phenyl-1,2,4-triazolin-3,5-dione adducts of vitamin D₃ (2 and1) withMCPBA yields two diastereomeric mixtures of the (5,10)-(7,8)-dioxiranes3 a,3 b,3 c and4 a,4 b respectively. The corresponding benzoates5 a,5 b,6 a and6 b were prepared and the X-ray crystal structure of5 b was determined. This analysis proved5 b to be the (5R, 1 OS)-(7R, 8R)-dioxirane of the β-resp. (6S)-4-phenyl-1,2,4-triazolin-3,5-dione adduct1 of vitamin D₃.     

Total synthesis of the mushroom metabolite (+)-calopin

A synthesis of (+)-calopin (1a) was achieved employing a highly stereoselective ene reaction between 8-phenylmenthyl glyoxylate (3) and the β,β-dimethylstyrene 4c. Transesterification of the resulting homoallylic alcohol 5c, followed by allylic oxidation and hydrogenation yielded the δ-lactone 13 which was deprotected to the natural product 1a.     

Practical and efficient synthesis of chiral 2,4-disubstituted oxazolines from β-phosphonoamides

Herein we report a practical and efficient method for the synthesis of optically active 2,4-disubstituted oxazolines (S)-1a–h in good to excellent yields. The target compounds were prepared in good yield through the Horner–Wadsworth–Emmons reaction of β-phosphonoamide 3 bearing l-phenylalaninol with commercially available aryl aldehydes followed by the cyclodehydration of the corresponding N-(cinnamoyl)-(S)-phenylalaninol derivatives (S)-2a–h. Additionally, the cyclodehydration of β-phosphonoamide (S)-3 followed by the Horner–Wadsworth–Emmons reaction of β-phosphono-oxazoline (S)-4 with aryl aldehydes also gave the 2,4-disubstituted oxazolines (S)-1a–h.     

ABOUT THE REACTION OF 2,3-DIBROMO-2-METHYL-N-(1-ADAMANTYL)-PROPANAMIDE WITH SODIUM TERT-BUTOXIDE. A COMPETITION EXPERIMENT

2,3-Dibromo-2-methyl-N-(1-adamantyl)propanamide (4), a precursor equally suited for the preparation of an α-lactam and a β-lactam, upon treatment with sodium tert-butoxide ether gives no α-lactam (5), but an excellent yield of the isomeric β-lactam, 1-(1-adamantyl)-3-bromo-3-methylazetidinone (6) as the only product. Repeating the experiment using a large excess of sodium tert-butoxide still leads to β-lactam 6 in 76.1% yield, but now accompanied by its dehydrobrominated derivative, β-lactam 7, in 17.4% yield, and no trace of α-lactam 5