Synthesis of novel 15-membered 8a-azahomoerythromycin A acylides: Consequences of structural modification at the C-3 and C-6 position on antibacterial activity.

A novel series of 6-O-substituted 8a-aza-8a-homoerythromycin A 3-O-acylides has been discovered with potent activity against key respiratory pathogens, including those inducibly and constitutively resistant to erythromycin. The best compounds in this series 15na and 15nd showed activity comparable to telithromycin, especially against Haemophilus influenzae and constitutively MLSB-resistant strains of Streptococcus pneumoniae and Streptococcus pyogenes. Furthermore, 15na exhibited a number of drug-like attributes including favorable pharmacokinetic properties and in vivo efficacy. For instance, 15na exhibited good oral bioavailability (average F = 42%) and demonstrated in vivo efficacy superior to telithromycin (1) against erythromycin-susceptible S. pneumoniae. As such, 15na has a significant potential for further development of this novel macrolide antibiotics class.

Synthesis and antibacterial evaluation of novel 4″-glycyl linked quinolyl-azithromycins with potent activity against macrolide-resistant pathogens.

A new azithromycin-based series of antibacterial macrolones is reported, which features the use of a 4″-ester linked glycin for tethering the quinolone side chain to the macrolide scaffold. Among the analogs prepared, compounds 9e and 22f with a quinolon-6-yl moiety were found to have potent and well-balanced activity against clinically important respiratory tract pathogens, including erythromycin-susceptible and MLSB resistant strains of Streptococcus pneumoniae, Streptococcus pyogenes, and Haemophilus influenzae. In addition, potential lead compounds 9e and 22f demonstrated outstanding levels of activity against Moraxella catarrhalis and inducibly MLSB resistant Staphylococcus aureus. The best member of this series 22f rivals or exceeds, in potency, some of the most active ketolide antibacterial agents known today, such as telithromycin and cethromycin.

Synthesis and Structure-Activity Relationships of α-Amino-γ-lactone Ketolides: A Novel Class of Macrolide Antibiotics.

An efficient synthesis of α-amino-γ-lactone ketolide (3) was developed, which provided a versatile intermediate for the incorporation of a variety of aryl and heteroaryl groups onto the C-21 position of clarithromycin via HBTU-mediated amidation. The biological data for this important new class of macrolides revealed significantly potent activity against erythromycin-susceptible strains as well as efflux-resistant and erythromycin MLSB-resistant strains of S. pneumoniae and S. pyogenes. In addition, ketolide 11o showed excellent in vitro antibacterial activity against H. influenzae strain as compared to telithromycin. These results indicate that C-21 substituted γ-lactone ketolides have potential as a next generation macrolide antibiotics.

Synthesis, activity and pharmacokinetics of novel antibacterial 15-membered ring macrolones.

Synthesis, antibacterial activity and pharmacokinetic properties of a novel class of macrolide antibiotics-macrolones-derived from azithromycin, comprising oxygen atom(s) in the linker and either free or esterified quinolone 3-carboxylic group, are reported. Selected compounds showed excellent antibacterial potency towards key erythromycin resistant respiratory pathogens. However, the majority of compounds lacked good bioavailability. The isopropyl ester, compound 35, and a macrolone derivative with an elongated linker 29 showed the best oral bioavailability in rats, both accompanied with an excellent overall microbiology profile addressing inducible and constitutive MLSb as well as efflux mediated macrolide resistance in streptococci, while compound 29 is more potent against staphylococci.

Discovery of 4''-ether linked azithromycin-quinolone hybrid series: influence of the central linker on the antibacterial activity.

A series of novel C-4''-substituted azithromycins was synthesized and evaluated for in vitro antibacterial activity against a panel of representative erythromycin-susceptible and macrolide-lincosamide-streptogramin (MLS) resistant pathogens. In summary, azithromycin and quinolone substructures merged in a mutually SAR-compatible design gave rise to a new class of antimicrobials with an improved spectrum and potency over azithromycin. Prototypical analogues 7f and 8f display an improved potency versus azithromycin against Gram-positive and fastidious Gram-negative pathogens. In particular, these new leads maintain activity against MLS-resistant strains of Streptococcus pneumoniae and Streptococcus pyogenes. In addition, they represent an improvement over telithromycin (1) and cethromycin (2) against the fastidious Gram-negative pathogen Haemophilus influenzae.

Novel hybrids of 15-membered 8a- and 9a-azahomoerythromycin A ketolides and quinolones as potent antibacterials.

A series of novel 6-O-substituted and 6,12-di-O-substituted 8a-aza-8a-homoerythromycin A and 9a-aza-9a-homoerythromycin A ketolides were synthesized and evaluated for in vitro antibacterial activity against a panel of representative erythromycin-susceptible and erythromycin-resistant test strains. Another series of ketolides based on 14-membered erythromycin oxime scaffold was also synthesized and their antibacterial activity compared to those of 15-membered azahomoerythromycin analogues. In general, structure-activity studies have shown that 14-membered ketolides displayed favorable antibacterial activity in comparison to their corresponding 15-membered analogues within 9a-azahomoerythromycin series. However, within 8a-azahomoerythromycin series, some compounds incorporating a ketolide combined with either quinoline or quinolone pharmacophore substructures showed significantly potent activity against a variety of erythromycin-susceptible and macrolide-lincosamide-streptogramin B (MLS(B))-resistant Gram-positive pathogens as well as fastidious Gram-negative pathogens. The best compounds in this series overcome all types of resistance in relevant clinical Gram-positive pathogens and display hitherto unprecedented in vitro activity against the constitutively MLS(B)-resistant strain of Staphylococcus aureus. In addition, they also represent an improvement over telithromycin (2) and cethromycin (3) against fastidious Gram-negative pathogens Haemophilus influenzae and Moraxella catarrhalis.

Synthesis and structure-activity relationships of novel 8a-aza-8a-homoerythromycin A ketolides.

A series of novel 6-O-substituted 8a-aza-8a-homoerythromycin A ketolides was synthesized and evaluated for in vitro antibacterial activity. Key strategic elements of the synthesis include the base-induced E-Z isomerization of 3-O-descladinosyl-6-O-allylerythromycin A 9(E)-oxime followed by ring-expanding reaction of the resulting 9(Z)-oxime via Beckmann rearrangement. The ketolides showed potent activity against a variety of erythromycin-susceptible and macrolide-lincosamide-streptogramin B (MLS(B)) resistant Gram-positive and fastidious Gram-negative pathogens. The best compounds in this series overcome all types of resistance in relevant clinical Gram-positive pathogens and display in vitro activity comparable to telithromycin and cethromycin.

Synthesis and biological activity of 4''-O-acyl derivatives of 14- and 15-membered macrolides linked to omega-quinolone-carboxylic unit.

The synthesis and antimicrobial activity of a new class of macrolide antibiotics which consist of a macrolide scaffold and a quinolone unit covalently connected by an appropriate linker are described. Optimization of several synthetic steps and structural properties of lead compound 26 are discussed. Promising antibacterial properties of this compound and some of its analogues are reported.

Novel 8a-aza-8a-homoerythromycin--4''-(3-substituted-amino)propionates with broad spectrum antibacterial activity.

Fifteen-membered 8a-aza-8a-homoerythromycins derived from either erythromycin or clarithromycin have been acylated to form 4''-O-propenoyl derivative. These functionalized analogues underwent Michael reaction with primary or secondary amines to afford novel 8a-aza-8a-homoerythromycin-4''-(3-substituted-amino)propionates. This preparative sequence was adapted so that analogues could be made by parallel synthesis. Among them, 4-quinolone derivatives show particularly good antibacterial potency against macrolide resistant bacteria, comparable or better than azithromycin and telithromycin.

Synthesis and biological properties of 4''-O-acyl derivatives of 8a-Aza-8a-homoerythromycin.

A series of 4''-O-acyl derivatives of 8a-aza-8a-homoerythromycins A were synthesized and tested against Gram-positive and Gram-negative bacteria. Derivatives of 8a-aza-8a-homoerythromycin A have potent anti-bacterial activity against not only azithromycin-susceptible strains, but also efflux (M) and inducible macrolide-lincosamide-streptogramin-resistant Gram-positive pathogens. These compounds show moderate to high clearance and low oral bioavailability in preliminary in vivo pharmacokinetic studies in rat.

Novel 9a-carbamoyl- and 9a-thiocarbamoyl-3-decladinosyl-6-hydroxy and 6-methoxy derivatives of 15-membered macrolides.

An efficient method for the synthesis of diverse 9a-carbamoyl- and 9a-thiocarbamoyl-3-decladinosyl-6-hydroxy and 3-decladinosyl-6-methoxy derivatives of 15-membered azalides has been developed. These derivatives bear various alkyl and aryl groups attached to macrolide scaffold through urea or thiourea moieties at 9a position. Chemical transformations of hydroxy group at position C-3 afforded range of ketolides, anhydrolides, hemiketals, cyclic ethers, and acylides. It has been shown that 6-hydroxy and 6-methoxy derivatives undergo different chemical transformations under otherwise identical reaction conditions. Antimicrobial properties of prepared compounds were evaluated.

Azalides from azithromycin to new azalide derivatives.

Azalides are semi-synthetic macrolides, in which a nitrogen atom is introduced into a macrolactone ring via a Beckmann rearrangement. Starting from erythromycin, oximes, depending on the reaction conditions lactams, or bicyclic-imino-ethers were formed, which were further reduced to aminolactones. The cyclic amine 9a- became the precursor for novel, significantly more active derivatives, especially for 9-dihydro-9-deoxo-9a-methyl-9a-aza-9a-homoerythromycin A with the generic name azithromycin. It showed a broad spectrum of antibacterial activity covering all significant bacteria causing respiratory tract infections. The greatest advantages of azithromycin are its unusual pharmacokinetics (high tissue distribution), metabolic stability and high tolerability. These properties have led in recent years to the widespread use of the azalide scaffold for the synthesis of new compounds with advantageous pharmacokinetics. The azalide scaffold possesses an amino and several hydroxyl groups, which could be substituted or transformed to obtain new compounds. Different derivatives were obtained by substitution on the nitrogen but a large variety of derivatives, such as ethers, esters and carbamates, were made by reactions with various hydroxyl groups. Substitutions on both nitrogen and hydroxyl or two hydroxyl groups yielded new, bridged compounds. The 4''-hydroxy group was oxidized to 4-oxo-, which was transformed via the oxime to 4-amino, or via epoxide to 4''-methylamino compounds. Cleavage of the cladinose sugar and further transformations gave 3-acyl or 3-oxo compounds, which were less active than 14-membered acylides or ketolides. Beckmann rearrangement of some 16-membered macrolide oximes yielded only 17-membered lactams, which were less active than starting macrolides, and could not be reduced to amines. Intramolecular rearrangement of azalide imino-ethers yielded 13-membered azalides. Some new 11a-azalides were obtained after oxidative cleavage of some 16-membered macrolides and additional cyclisation.

Synthesis and antibacterial activity of isomeric 15-membered azalides.

A series of 3-keto and 3-O-acyl derivatives of both 6-O-alkyl-8a-aza-8a-homoerythromycin A and 6-O-alkyl-9a-aza-9a-homo-erythromycin A were synthesised and tested against Gram-positive and Gram-negative bacteria. Derivatives of 8a-aza-8a-homoerythromycin A have potent antibacterial activity against not only azithromycin-susceptible strains, but also efflux (M) and inducible macrolide-lincosamide-streptogramin (iMLSB) resistant Gram-positive pathogens, while the corresponding 9a-isomers were less active. Introduction of an additional ring such as 11,12-cyclic carbonate reduced antibacterial activity of both series. 3-Keto and 3-O-(4-nitrophenyl)-acetyl derivatives of 6-O-methyl-8a-aza-8a-homo-erythromycin A show typical macrolide pharmacokinetics in preliminary in vivo studies in mice, and their in vivo efficacy is demonstrated.

Semisynthetic macrolide antibacterials derived from tylosin. Synthesis and structure-activity relationships of novel desmycosin analogues.

A series of 20-O-substituted and 3,20-di-O-substituted derivatives of desmycosin were synthesized and their biological properties were evaluated. In particular, we have synthesized numerous side chain modified analogues of desmycosin as well as some analogues possessing a combination of modified side chain and alternative C-3 substituents. Thus, alpha,beta-unsaturated analogues of desmycosin (2), tylosin (1), 10,11,12,13-tetrahydrotylosin (11), and 2,3-didehydrodesmycosin (13) were prepared from the corresponding aldehydes by a Wittig reaction with the stabilized ylides (a-d), generating a trans-double bond, followed by modified Pfitzner-Moffat oxidation of the C-3 hydroxyl group. To evaluate the importance of the C-3 position of desmycosin for biological activity, the C-3 substituted derivatives were synthesized by a standard sequence of protective group chemistry followed by Wittig reaction and esterification as the key steps. For the attachment of the C-3 ester functionality, a mixed anhydride protocol was adopted. Reaction proceeded smoothly to give corresponding esters in yields ranging from 70 to 80%. Base- and acid-catalyzed rearrangement products including desmycosin 8,20-aldols (24a and 24b) and desmycosin 3,19-aldol (25) are also described. Parallel array synthesis and purification techniques allowed for the rapid exploration of structure-activity relationships within this class and for the improvement in potency. In vitro evaluation of these derivatives demonstrated good antimicrobial activity against Gram-positive bacteria for most of the compounds. The present derivatives of 16-membered macrolides were active against MLS(B)-resistant strains that were inducibly resistant, but not those constitutively resistant to erythromycin.

New amidino-benzimidazolyl derivatives of tylosin and desmycosin.

New amidino-benzimidazolyl derivatives of antibiotics tylosin and desmycosin are prepared in the reaction of corresponding amidino-substituted o-phenylendiamine with tylosin respectively desmyicosin on the 20-C aldehyde group. The reaction was carried out in absolute ethanol in the presence ofp-benzoquinone. On this way are prepared: 20-[5-(N-isopropylamidino)-2-benzimidazolyl]tylosin hydrochloride 9, 20-[5-(2-imidazolinyl)-2-benzimidazolyl]tylosin hydrochloride 10, 20-[5-(N-morpholinylamidino)-2-benzimidazolyl]tylosin hydrochloride 11, 20-[5-(N-isopropylamidino)-2-benzimidazolyl]desmycosin hydrochloride 12, 20-[5-(2-imidazolinyl)-2-benzimidazolyl]desmycosin hydrochloride 13, 20-[5-(N-morpholinylamidino)-2-benzimidazolyl]desmycosin hydrochloride 14. Their antimicrobial activity was tested on a series of microorganisms.