Isoxazoline derivatives as potential inhibitors of the proteolytic enzymes human leukocyte elastase, cathepsin G and proteinase 3: a structure-activity relationship study

A Facile Synthesis of 2,5-Dihydroisoxazoles via an Organoselenium-Induced Stereoselective Cyclisation and Deselenylation Reaction

The organoselenium-induced ring-closure reactions of O-allyl oximes give cyclic iminium salts that can be reduced in situ with NaBH4 to produce N-alkyl-4–phenylselenoisoxazolidines; selenoxide syn-elimination follows to form 2, 5-dihydroisoxazoles in good yields.

Design and synthesis of D-ring steroidal isoxazolines and oxazolines as potential antiproliferative agents against LNCaP, PC-3 and DU-145 cells

Two series of novel steroidal isoxazolines and oxazolines were synthesized through different routes from dehydroepiandrosterone acetate and pregnenolone acetate, respectively. The synthesis of the analogs of both series is multistep and proceeds in good overall yields. While the key step in the synthesis of former is the cycloaddition of aromatic nitrile oxides across α,β-unsaturated olefins, it is the condensation of α,β-azidoalcohols with aromatic aldehydes in the later. Compounds of both the series were tested for their cytotoxic activities against LNCaP, PC-3 and DU-145 prostate cancer cell lines. Amongst all the compounds of both the series screened for their prostate cancer activity, compound 6a, 6e and 12a are the most active especially against LNCaP and DU-145 cancer cell lines.

Synthesis of novel steroidal D-ring substituted isoxazoline derivatives of 17-oxoandrostanes

A facile synthesis of isoxazoline derivatives of 17-oxoandrostane at the side chain of D-ring is reported. The scheme involves the transformation of the starting dehydroepiandrosterone acetate (ketone) to the Knoevenegel product, reduction to the nitrile, and elimination to the carboxaldehyde. Cycloaddition of nitrileoxides across olefinic aldehyde intermediate led to the synthesis of novel side chain isoxazoline derivatives.

Novel Synthesis of 1,3,5-Trisubstituted 2-Pyrazolines Promoted by Chlorotrimethylsilane

1,3,5-Trisubstituted-2-pyrazolines were effectively synthesised by utilising chlorotrimethylsilane as an efficient promoter in the cyclisation addition of phenylhydrazine to chalcones under nitrogen in acetonitrile. The clean, mild reaction conditions, high yields and a simple workup of target compounds were attractive features of the reaction which enables a facile preparative procedure for building the pyrazoline ring.

Discovery of novel isoxazolines as anti-tuberculosis agents

Nitrofuranyl isoxazolines with increased proteolytic stability over nitrofuranyl amides were designed and synthesized leading to discovery of several compounds with potent in vitro anti-tuberculosis activity. However, their in vivo activity was limited by high protein binding and poor distribution. Consequently, a series of non-nitrofuran containing isoxazolines were prepared to determine if the core had residual anti-tuberculosis activity. This led to the discovery of novel isoxazoline 12 as anti-tuberculosis agent with a MIC(90) value of 1.56microg/mL.

One-pot synthesis of functionalized 4,5-dihydroisoxazole derivatives via nitrile oxides and biological evaluation with plant cells

1,3 Dipolar cycloadditions of nitrile oxides generated in situ in the presence of a variety of olefins provided 4,5-dihydroisoxazoles. The whole procedure could be performed in a practical and efficient one-pot operation. The products are of excellent purity (95%) and are isolated in 60-83% yields. Some of them enhanced the accumulation of indole alkaloids in periwinkle cell cultures.

1-Alkoxycarbonyl-3-halogenoazetidin-2-ones as elastase (PPE) inhibitors

A series of 1-alkoxycarbonyl-3-halogenoazetidin-2-ones, designed as potential suicide inhibitors of serine proteases, has been synthesized and evaluated against porcine pancreatic elastase (PPE). All the compounds were transient inhibitors, their activity depending mainly on the nature of the halogen substituent: bromo- and iodo- derivatives are more active (K(i) approximately 2-22 microM) than 3-chloroazetidinones (K(i) approximately 20-150 microM). The lipophilicity of the N-1 substituent appeared to exert a slightly positive effect.

Solid-phase synthesis of novel isoxazolocyclobutanones and isoxazolinocyclobutenones

[reaction: see text] The preparation of novel isoxazolocyclobutanone and isoxazolinocyclobutenone derivatives via a traceless solid-phase sulfone linker strategy is described. Key steps in the solid-phase protocol reported here include (i) sulfinate right arrow sulfone alkylation, (ii) four-member ring formation by sulfone dianion alkylation, (iii) heterocycle formation by nitrile oxide 1,3-dipolar cycloaddition, and (iv) traceless product release by cyclobutanol right arrow cyclobutanone oxidation with concomitant linker cleavage by sulfinate elimination.

Preparation of a 990-member chemical compound library of hydantoin- and isoxazoline-containing heterocycles using multipin technology

The development of a useful chemistry for the construction of polyfunctional heterocycles--first through solution and solid phase (resins) and then library production via SynPhase crowns--is reported. Bead-based synthetic work was done on Merrifield resin where treatment with benzylamine in the presence of DBU followed by reaction with 4-chloromethylbenzoyl chloride afforded amide-linked resin 9. Finally, TFA.NH2-polystyrene macro crowns were derivatized with 4-(hydroxymethyl)benzoic acid to afford pin 14 which was coupled with Boc-protected amino acid 2 in the presence of DIC to deliver pin 15. Deprotection and reaction with phenyl isocyanate afforded urea functionalized pin 17 which underwent 1,3-dipolar cycloaddition reaction to give pin 19. Finally, compound 20 was obtained with moderate diastereoselectivity (20:21::8:1) by the reaction of pin 19 with a catalytic amount of Et3N.

Diastereoselective synthesis of hydantoin- and isoxazoline-substituted dispirocyclobutanoids

Synthetic strategies for constructing novel achiral cyclobutanoid isoxazolidinoimidazolidinedione heterocycles, with a generalized structure of II, have been developed via 1,3-dipolar cycloaddition and carbanilide cyclization transformations from methylenecyclobutane 13. The exo methylene cyclobutane system has made the realization of some diasteroselectivity possible, such that the H-bond (Boc-NH) directed product (i.e., 14) was obtained with 3:1 selectivity relative to the non-H-bond directed product (i.e., 15).

6-Acylamino-2-[(alkylsulfonyl)oxy]-1H-isoindole-1,3-dione mechanism-based inhibitors of human leukocyte elastase

A study of various 2-[(alkylsulfonyl)oxy]-6-substituted-1H-isoindole-1,3-diones' inhibition of chymotrypsin compared to inhibition of HLE reveals that acylamino substitution in the 6-position increases selectivity and potency of these inhibitors for HLE. The best HLE inhibitor in this series was 6-(methylglutaryl)amino-2-[(ethylsulfonyl)oxy]-1H-isoindole-1,3-di one with a kobs/[I] = 220,000 M(-1) s(-1).

Diastereoselective Synthesis of Cyclopentanoids with Hydantoin and Isoxazoline Substituents

Exploiting 1,3-dipolar cycloaddition and urea --> hydantoin cyclization transformations, novel spiro[cyclopenta[d]isoxazole-4',5-imidazolindine] heterocycles of generalized structure I have been prepared. The 1-amino-3-cyclopentenecarboxylate precursor II was prepared from a suitably activated/protected derivative of glycine and the bis-alkylating agent cis-1,4-dichloro-2-butene.