An alternative synthesis of the 1-oxacephem skeleton

1-Oxacephem skeletons were constructed in a convergent manner starting from building blocks $\text{B}$ and $\text{C}$, which were easily prepared from penicillin and diketene, respectively, followed by intramolecular carbene insertion reaction of the resulting intermediate $\text{A}$.     

Design,synthesis and antibacterial activity of novel 1-oxacephem analogs

A series of l-oxacephem analogs were synthesized and their antibacterial properties against five strains of Gram-positive and Gram-negative bacteria were evaluated in vitro while ceftazidine was selected as control. Some of the tested compounds, compound 2c in narticular,showed more active aeainst three selected strains than the standard.     

A chemical conversion of penicillin sulfoxides into 6,7-epi-1-oxocephams

Penicillin sulfoxides were converted into 6,7-epi-1-oxocephams by a simple and efficient method. The oxidation of 1,2-seco-Δ²-cephem with osmium tetroxide provided 1,2 diol 5 which was then converted to the chloro-β-lactams 6. Treatment of 6 with tin (II) chloride or silver tetrafluoroborate afforded 6,7-epi-1-oxocephams 2,3. Several reactions were attempted to obtain 1-oxo-exomethylene cephalosporins 13,15 from the oxazoline 11 prepared from the exomethylene cephalosporin 8.     

The trapping of sulfenic acids from penicillin sulfoxides. Ethyl 2-mercaptoacetate

The thermolysis of trichloroethyl 6-phenoxyacetamido penicillanate sulfoxide and ethyl 2-mercaptoacetate in toluene gave the unsym-azetidinone disulfide(β,γ-isomer) in 65% yield. With added catalytic amounts of N,N-dimethylaniline the α,β-isomer was the major product (60%), along with a $\text{new}$ β-lactam cleaved product, $\text{8}$ (5–6%).     

One-step synthesis of SBA-15 containing tungsten oxide nanoclusters: a chemoselective catalyst for oxidation of sulfides to sulfoxides under ambient conditions

Tungsten oxide nanoclusters supported highly ordered mesoporous SBA-15 material has been successfully synthesized in a single step using a non-ionic surfactant as a template and used for the selective oxidation of sulfur compounds, giving excellent yields at room temperature with exceptional catalyst recyclability.     

Thermal rearrangement of 1,3-thiazolidine sulfoxides: Thiolsulfinate and thioaldehyde intermediates

Stereospecific ring opening of the sulfoxides cis- 13 and trans- 14 in refluxing toluene gave the corre sponding sulfenic acids 9 , 10 intermediates respectively. The sulfenic acid 9 dimerized to the thiolsulfinate 17 by dual function of the sulfenic acid as S-nucleophile/S-electrophile with loss of water while the sulfenic acid 10 was unchanged. The stereospecific recyclization of 10 to the parent sulfoxide 14 increases the higher pi-electron density of the double. The thermolysis of the thiolsulfinate 17 gave the transient sulfenic acid 9 , which dimerized again to repeat the process and unisolable thioaldehyde 21 . The thioaldehyde 21 was con verted to either pyrrole 15 by the action of a sulfinic acid 20 catalyst formed inevitably by hydrolysis of 17 under the reaction conditions, or thiazole 18 under neutral conditions. In these rearrangements, the amide carbonyl group facilitated the elimination of a neighboring hydrogen.     

The synthesis of malonimide derivatives as potential penicillin analogs

Malonimidoacetic acid derivatives (VIII, XIII) were synthesized as a potential penicillin analogs, hut they failed to inhibit the growth of bacteria when tested in vitro against a range of Gram-positive and Gram-negative microorganisms.     

Studies on hydrozirconation of 1-alkynyl sulfoxides or sulfones and the application for the synthesis of stereodefined vinyl sulfoxides or sulfones

The hydrozirconation reaction of 1-alkynyl sulfoxides or sulfones with Cp2Zr(H)Cl in THF at room temperature predominantly gave Z-beta-zirconated vinyl sulfoxides or sulfones with excellent regioselectivity. Compared with 1-alkynyl sulfoxides, the hydrozirconation reaction of 1-alkynyl sulfones exhibits great synthetic potential, leading to the efficient preparation of Z-beta-halovinyl sulfones, Z-beta-sulfonyl alpha,beta-unsaturated ketones, and Z-beta-alkynyl vinyl sulfones. Although the reaction mechanisms are still not clear, the neighboring group participation of the sulfinyl or sulfonyl group may be playing an important role in this unique hydrozirconation reaction.     

One-step synthesis of biotinyl photoprobes from unprotected carbohydrates

A simple and versatile approach for the preparation of carbohydrate photoprobes has been developed. By a single-step reaction at 37 degrees C, a biotinylated carbene-generating unit was introduced to the reducing end of unprotected carbohydrates. Micromole quantities of N-acetyllactosamine, Lewis X trisaccharide, and sialyl Lewis X tetrasaccharide were easily converted to their biotinylated photoreactive analogues, which enabled the nonradioisotopic chemiluminescent detection of the photolabeled products. Thus, a sequence of lectin photoaffinity labeling, from the probe synthesis to the detection of labeled protein, was readily accomplished within one week. Our strategy may be applicable to any aldehyde-bearing ligand.     

Stereospecific synthesis of alpha- and beta-C-glycosides from glycosyl sulfoxides: scope and limitations

C-Glycosides derived from alpha-L-fuco-, alpha-D-gluco-, beta-D-gluco-, and alpha-D-mannopyranose have been synthesized from the corresponding glycosyl phenyl sulfoxide through phenylsulfinyl-lithium exchange, to generate an anomeric carbanion, and subsequent reaction with a carbon electrophile. The reactions were stereospecific and proceeded with retention of the configuration at the anomeric center. Improved yields of C-glycosides were obtained by an inverse addition protocol. Trapping of the anomeric carbanion with aldehydes gave best results. Reaction with ketones, chloroformates, nitriles, and alkyl halides was also explored. Mechanistic aspects of the reaction are discussed.     

One-step synthesis of (1-iodovinyl) arenes from trimethylsilyl ethynylarene through iodotrimethylsilane-mediated hydroiodation

One-step access to (1-iodovinyl) arenes from trimethylsilyl ethynylarenes is described. The method is superior to a conventional multi-step approach, and is enhanced by the Sonogashira reaction that provides ready access to a variety of trimethylsilyl ethynylarenes.