Synthesis of isothiochroman 2,2-dioxide and 1,2-benzooxathiin 2,2-dioxide gyrase B inhibitors

1,2-Benzoxathiin-4(3H)-one 2,2-dioxide - new enol nucleophile in three-component interaction with benzaldehydes and active methylene nitriles

The reactivity of 1,2-benzoxathiin-4(3H)-one 2,2-dioxide was studied in multicomponent type reactions for the first time, namely, in a three-component interaction with active methylene nitriles and aromatic aldehydes in order to construct condensed 2-amino-4H-pyran derivatives. The reaction outcome strongly depended on the nature of an active methylene nitrile and an arenecarbaldehyde. Application of malononitrile resulted in novel 2-amino-4-aryl-4H-pyrano[3,2-c][1,2]benzoxathiine-3-carbonitrile 5,5-dioxides in most cases, whereas the utilization of ethyl cyanoacetate resulted in a complex mixture of products. In the last case, three different products were isolated depending on the arenecarbaldehyde used, namely ethyl 2-amino-4-aryl-4H-pyrano[3,2-c][1,2]benzoxathiine-3-carboxylate 5,5-dioxides, ethyl 2-cyano-3-arylacrylates, and salts of 3,3′-(arylmethylene)bis(4-hydroxybenzo[e][1,2]oxathiine 2,2-dioxides). Attempts to obtain separately ethyl 2-amino-4-aryl-4H-pyrano[3,2-c][1,2]benzoxathiine-3-carboxylate 5,5-dioxides enabled us to propose reaction pathways leading to these products. The salts were obtained for the first time. The preparative method for the synthesis of triethylammonium salts of 3,3′-(arylmethylene)bis(4-hydroxybenzo[e][1,2]oxathiine 2,2-dioxides) was proposed by the direct interaction of 1,2-benzoxathiin-4(3H)-one 2,2-dioxide with arenecarbaldehydes. The application of ammonium acetate as a catalyst allowed us to synthesize 7-aryl-7,14-dihydrobenzo[5,6][1,2]oxathiino[4,3-b]benzo[5,6][1,2]oxathiino[3,4-e]pyridine 6,6,8,8-tetraoxides containing a novel heterocyclic system. These facts, combined with our past investigations, allowed us to assert that the reactivity of enol nucleophiles that include the COCH₂SO₂X fragment has not been reported previously.

Reactivity of 1,2-benzoxathiin-4(3H)-one 2,2-dioxide was for the first time studied in multicomponent type reactions involving active methylene nitriles and aromatic aldehydes.

Mannich reaction derivatives of novobiocin with modulated physiochemical properties and their antibacterial activities

Synthetic derivatives of the natural product antibiotic novobiocin were synthesized in order to improve their physiochemical properties. A Mannich reaction was used to introduce new side chains at a solvent-exposed position of the molecule, and a diverse panel of functional groups was evaluated at this position. Novobiocin and the new derivatives were tested for their binding to gyrase B and their antibacterial activities against Staphylococcus aureus, Mycobacterium tuberculosis, Francisella tularensis and Escherichia coli. While the new derivatives still bound the gyrase B protein potently (0.07-1.8 μM, IC(50)), they had significantly less antibacterial activity. Two compounds were identified with increased antibacterial activity against M. tuberculosis, with a minimum inhibitory concentration of 2.5 μg/ml.

Coumabiocins A-F, aminocoumarins from an organic extract of Streptomyces sp. L-4-4

Bioassay-directed fractionation of the butanol extract of Streptomyces sp. L-4-4, using the hyphae formation inhibition assay of a prokaryotic whole cell, led to the isolation of six new aminocoumarins, coumabiocins A-F (1-6), along with two known compounds, novobiocin (7) and isonovobiocin (8). Coumabiocins A-E (1-5) contain three structural elements, a central 3-amino-7-hydroxycoumarin that is linked at the 3-amino group to a prenylated 4-hydroxybenzoic acid moiety and at the 7-position to an l-noviosyl sugar, while coumabiocin F (6) lacks the sugar moiety. Their structures were elucidated by spectroscopic methods including 1D- and 2D-NMR techniques and mass spectrometric analyses. Coumabiocins A-E (1-5) exhibited significant inhibitory activity against Streptomyces 85E and gave a 10-15 mm clear zone of inhibition at 20 microg/disk and a 10 mm bald and a 10 mm clear zone of inhibition at 5 and 10 microg/disk, respectively, whereas coumabiocin F (6) was inactive.

Syntheses of photolabile novobiocin analogues

Novobiocin was recently shown to inhibit Hsp90 through a previously unrecognized C-terminal ATP binding site. Although the N-terminal region of Hsp90 has been solved by X-ray crystallography, the C-terminal region has not. In an effort to elucidate the C-terminal binding site of Hsp90, four photolabile analogues of novobiocin were prepared.

Antimicrobial and DNA gyrase-inhibitory activities of novel clorobiocin derivatives produced by mutasynthesis

Twenty-eight novel clorobiocin derivatives obtained from mutasynthesis experiments were investigated for their inhibitory activity towards Escherichia coli DNA gyrase and for their antibacterial activities towards clinically relevant gram-positive and gram-negative bacteria in comparison to novobiocin and clorobiocin. Clorobiocin was the most active compound both against E. coli DNA gyrase in vitro and against bacterial growth. All tested modifications of the 3-dimethylallyl-4-hydroxybenzoyl moiety reduced biological activity. The highest activities were shown by compounds containing a hydrophobic alkyl substituent at position 3 of the 4-hydroxybenzoyl moiety. Polar groups in this side chain, especially amide functions, strongly reduced antibacterial activity. Replacement of the alkyl side chain with a halogen atom or a methoxy group at the same position markedly reduced activity. Transfer of the pyrrole carboxylic acid moiety from O-3" to O-2" of L-noviose moderately reduced activity, whereas the complete absence of the pyrrole carboxylic acid moiety led to a loss of activity. Desclorobiocin derivatives lacking the chlorine atom at C-8 of the 3-amino-4,7-dihydroxycoumarin moiety also showed low activity. Lack of a methyl group at O-4" of L-noviose resulted in an inactive compound. From these findings it appears that clorobiocin represents a "highly evolved" structure optimized for bacterial transport and DNA gyrase inhibition.

D-Gulonolactone as a synthon for L-noviose: first preparation of 4-O-demethyl-L-noviofuranose and related derivatives

[reaction: see text] A new synthesis of L-noviose (11), a sugar moiety of novobiocin, is presented. D-Gulonolactone was initially converted in a few steps to the key ester derivative 7 [1-O-benzyl methyl 2,3-O-(1-methylethylidene)-alpha-L-lyxofuranosiduronate]. An appropriate selection of protecting groups enabled transformation of 7 under mild reaction conditions to 4-O-demethyl-L-noviofuranose 9a and related 9b-c. Derivatives 9 were further converted either to L-lyxopyranoses (10a and 10b) or to methyl L-lyxofuranoside 12.

Identification of the coumermycin A(1) biosynthetic gene cluster of Streptomyces rishiriensis DSM 40489

The biosynthetic gene cluster of the aminocoumarin antibiotic coumermycin A(1) was cloned by screening of a cosmid library of Streptomyces rishiriensis DSM 40489 with heterologous probes from a dTDP-glucose 4,6-dehydratase gene, involved in deoxysugar biosynthesis, and from the aminocoumarin resistance gyrase gene gyrB(r). Sequence analysis of a 30.8-kb region upstream of gyrB(r) revealed the presence of 28 complete open reading frames (ORFs). Fifteen of the identified ORFs showed, on average, 84% identity to corresponding ORFs in the biosynthetic gene cluster of novobiocin, another aminocoumarin antibiotic. Possible functions of 17 ORFs in the biosynthesis of coumermycin A(1) could be assigned by comparison with sequences in GenBank. Experimental proof for the function of the identified gene cluster was provided by an insertional gene inactivation experiment, which resulted in an abolishment of coumermycin A(1) production.