Optimization of LpxC Inhibitors for Antibacterial Activity and Cardiovascular Safety.

UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a Zn2+ deacetylase that is essential for the survival of most pathogenic Gram-negative bacteria. ACHN-975 (N-((S)-3-amino-1-(hydroxyamino)-3-methyl-1-oxobutan-2-yl)-4-(((1R,2R)-2-(hydroxymethyl)cyclopropyl)buta-1,3-diyn-1-yl)benzamide) was the first LpxC inhibitor to reach human clinical testing and was discovered to have a dose-limiting cardiovascular toxicity of transient hypotension without compensatory tachycardia. Herein we report the effort beyond ACHN-975 to discover LpxC inhibitors optimized for enzyme potency, antibacterial activity, pharmacokinetics, and cardiovascular safety. Based on its overall profile, compound 26 (LPXC-516, (S)-N-(2-(hydroxyamino)-1-(3-methoxy-1,1-dioxidothietan-3-yl)-2-oxoethyl)-4-(6-hydroxyhexa-1,3-diyn-1-yl)benzamide) was chosen for further development. A phosphate prodrug of 26 was developed that provided a solubility of >30 mg mL-1 for parenteral administration and conversion into the active drug with a t1/2 of approximately two minutes. Unexpectedly, and despite our optimization efforts, the prodrug of 26 still possesses a therapeutic window insufficient to support further clinical development.

N'-(alpha-aminoacyl)- and N'-alpha-(N(alpha)-alkylamino)acyl derivatives of vancomycin and eremomycin. I. Synthesis of N'-(alpha-aminoacyl)- and N'-alpha-(N(alpha)-alkylamino)acyl derivatives of vancomycin and eremomycin by selective aminoacylation of the amino sugar of the disaccharide branch.

The acylation of unprotected vancomycin or eremomycin with activated esters of N(alpha)-protected amino acids or N(alpha)-alkyl-N(alpha)-Fmoc-amino acids is directed selectively to the amino group of the disaccharide branch (N') and after Fmoc-group removal leads to the corresponding N'-alpha-aminoacyl derivatives. A series of N'-alpha-aminoacyl and N'-alpha-(N(alpha)-alkylamino)acyl derivatives of eremomycin and vancomycin containing hydrophobic moieties has been synthesized. The structures of all derivatives were confirmed by Electrospray Ionization mass-spectral (ESI MS) analysis, and by chemical degradation methods. Position of the introduced N'-alpha-aminoacyl- and N-(N(alpha)-alkylamino)acyl groups were determined after Edman degradation and acidic hydrolysis. The structures of the synthesized starting reagents (N(alpha)-alkylamino acids or N(alpha)-alkyl-N(alpha)-Fmocamino acids) were confirmed by NMR-spectra data. In general, N'-(N-alkylglycyl)-derivatives were more active than the corresponding N'-alpha-(N(alpha)-alkylamino)acylated derivatives containing other amino acids (L-Lys, L-Met, L-Orn, L- and D-Ala, L- and D-Phe and benzyl-O-L-Tyr).

N'-(alpha-aminoacyl)- and N'-alpha-(N-alkylamino)acyl derivatives of vancomycin and eremomycin. II. Antibacterial activity of N'-(alpha-aminoacyl)- and N'-alpha-(N-alkylamino)acyl derivatives of vancomycin and eremomycin.

The antibacterial activities of the series of novel N'-(alpha-aminoacyl)- and N'-alpha-(N-akylamino)acyl derivatives of eremomycin and vancomycin containing hydrophobic moieties have been investigated. The N'-(N-alkylglycyl) derivatives of vancomycin are more active against vancomycin-susceptible staphylococci and enterococci and glycopeptide intermediate-resistant Staphylococcus aureus (GISA) than the corresponding eremomycin derivatives, but except for N'-[N-(p-octyloxybenzyl)glycyl-vancomycin] (28) and N'-[N-(p-octyloxybenzyl)-L-alanyl-vancomycin (33)--they are less active against glycopeptide-resistant enterococci (GRE). Derivatives 28 and 33 are the most active compounds (MIC's for glycopeptide-sensitive staphylococci and enterococci are 0.25 approximately 1 microg/ml, for GISA 1 approximately 2 microg/ml, for GRE 2 approximately 6 microg/ml). In in vivo studies, derivative 28 was active against S. aureus infections in mice with ED(50) 1 mg/kg versus 2 mg/kg for vancomycin (iv). In general N'-(N-alkylglycyl)-derivatives of vancomycin and eremomycin were more active than the corresponding N'-aminoacylated derivatives of these antibiotics containing other than glycin amino acids (L-Lys, L-Met, L-Orn, L- and D-Ala) and also L- and D-Phe or benzyl-O-L-Tyr.

Synthesis and antimalarial activity of new isotebuquine analogues.

Amodiaquine (AQ) and tebuquine are 4-aminoquinoline antimalarials with Mannich base side chain and are highly effective against chloroquine (CQ)-resistant strains of Plasmodium falciparum. Clinical use of AQ has been severely restricted due to hepatoxicity and agranulocytosis side effects associated with its long term use. Lysosomal accumulation and bioactivation to generate reactive quinoneimine metabolite are implicated to be the cause of the observed AQ toxicities. To avoid the quinoneimine formation and thus the toxicity, a series of isotebuquine analogues and their Nomega-oxides with hydroxy group meta to the amino rather than in para position of the aniline moiety were prepared. The new Mannich bases are highly active against both CQ-sensitive (D6) and -resistant (W2 and TM91C235) clones of P. falciparum with IC50 in the range of 0.3-120 ng/mL. New compounds are1000-fold less toxic (IC50 = 0.7-6 microg/mL) to mouse macrophage cell line than to parasite cell lines. Mono-Mannich bases are more active than bis-Mannich bases. Mono-Mannich base 1a (IC50 = 0.3 ng/mL) is 20-fold more active than the corresponding trifluoromethyl analogue 1b. No appreciable difference in either toxicity or efficacy were observed between the new Mannich bases (m-hydroxyaniline derivatives) 1a or 2a and the corresponding p-hydroxyaniline derivatives.

Antiretroviral activity of semisynthetic derivatives of glycopeptide antibiotics.

A variety of semisynthetic derivatives of natural antibacterial glycopeptide antibiotics such as vancomycin, eremomycin, ristocetin A, teicoplanin A(2)-2, DA-40926, their aglycons, and also the products of their partial degradation with a destroyed or modified peptide core show marked anti-retroviral activity in cell culture. In particular, aglycon antibiotic derivatives containing various substituents of a preferably hydrophobic nature displayed activity against human immunodeficiency virus type 1 (HIV-1), HIV-2, and Moloney murine sarcoma virus at a 50% inhibitory concentration in the lower micromolar (1-5 microM) concentration range while not being cytostatic against human lymphocytic cells at 250 microM or higher. The mode of anti-HIV action of the antibiotic aglycon derivatives could be ascribed to inhibition of the viral entry process.

Characterization of HERG potassium channel inhibition using CoMSiA 3D QSAR and homology modeling approaches.

A data set consisting of twenty-two sertindole analogues and ten structurally diverse inhibitors, spanning a wide range in potency, was analyzed using CoMSiA. A homology model of HERG was constructed from the crystal structure of the open MthK potassium channel. A complementary relationship between our CoMSiA and homology models is apparent when the long inhibitor axis is oriented parallel to the longitudinal axis of the pore, with the tail region pointed toward the selectivity filter. The key elements of the pharmacophore, the CoMSiA and the homology model are: (1) The hydrophobic feature optimally consists of an aromatic group that is capable of engaging in pi-stacking with a Phe656 side chain. Optionally, a second aromatic or hydrophobic group present in some inhibitors may contact an additional Phe656 side chain. (2) The basic nitrogen appears to undergo a pi-cation interaction with Tyr652. (3) The pore diameter (12A+), and depth of the selectivity loop relative to the intracellular opening, act as constraints on the conformation-dependent inhibitor dimensions.