Search

Apramycin is a structurally unique member of the 2-deoxystreptamine class of aminoglycoside antibiotics characterized by a monosubstituted 2-deoxystreptamine ring that carries an unusual bicyclic eight-carbon dialdose moiety. Because of its unusual structure, apramycin is not susceptible to the most prevalent mechanisms of aminoglycoside resistance including the aminoglycoside-modifying enzymes and the ribosomal methyltransferases whose widespread presence severely compromises all aminoglycosides in current clinical practice. These attributes coupled with minimal ototoxocity in animal models combine to make apramycin an excellent starting point for the development of next-generation aminoglycoside antibiotics for the treatment of multidrug-resistant bacterial infections, particularly the ESKAPE pathogens. With this in mind, we describe the design, synthesis, and evaluation of three series of apramycin derivatives, all functionalized at the 5-position, with the goals of increasing the antibacterial potency without sacrificing selectivity between bacterial and eukaryotic ribosomes and of overcoming the rare aminoglycoside acetyltransferase (3)-IV class of aminoglycoside-modifying enzymes that constitutes the only documented mechanism of antimicrobial resistance to apramycin. We show that several apramycin-5-O-β-d-ribofuranosides, 5-O-β-d-eryrthofuranosides, and even simple 5-O-aminoalkyl ethers are effective in this respect through the use of cell-free translation assays with wild-type bacterial and humanized bacterial ribosomes and of extensive antibacterial assays with wild-type and resistant Gram negative bacteria carrying either single or multiple resistance determinants. Ex vivo studies with mouse cochlear explants confirm the low levels of ototoxicity predicted on the basis of selectivity at the target level, while the mouse thigh infection model was used to demonstrate the superiority of an apramycin-5-O-glycoside in reducing the bacterial burden in vivo.

Propylamycin (4'-deoxy-4'-propylparomomycin) is a next generation aminoglycoside antibiotic that displays increased antibacterial potency over the parent, coupled with reduced susceptibility to resistance determinants and reduced ototoxicity in the guinea pig model. Propylamycin nevertheless is inactivated by APH(3')-Ia, a specific aminoglycoside phosphotransferase isozyme that acts on the primary hydroxy group of the ribofuranosyl moiety (at the 5''-position). To overcome this problem, we have prepared and studied the antibacterial and antiribosomal activity of various propylamycin derivatives carrying amino or substituted amino groups at the 5''-position in place of the vulnerable hydroxy group. We find that the introduction of an additional basic amino group at this position, while overcoming the action of the aminoglycoside phosphoryltransferase isozymes acting at the 5''-position as anticipated, results in a significant drop in selectivity for the bacterial over the eukaryotic ribosomes that is predictive of increased ototoxicity. In contrast, 5''-deoxy-5''-formamidopropylamycin retains the excellent across-the-board levels of antibacterial activity of propylamycin itself, while circumventing the action of the offending aminoglycoside phosphotransferase isozymes and affording even greater selectivity for the bacterial over the eukaryotic ribosomes. Other modifications to address the susceptibility of propylamycin to the APH(3')-Ia isozyme including deoxygenation at the 3'-position and incorporation of a 6',5''-bis(hydroxyethylamino) modification offer no particular advantage.

Herein, we report a strategy for the total synthesis of a structurally unique fungal glycolipid fusaroside. The first total synthesis of the proposed structure involved construction of the complex, branched lipid chain having a variety of alkenes with

Mycobacterium tuberculosis (Mtb) serves as the epitome of how lipids-next to proteins-are utilized as central effectors in pathogenesis. It synthesizes an arsenal of structurally atypical lipids (C60-C90) to impact various membrane-dependent steps involved in host interactions. There is a growing precedent to support insertion of these exposed lipids into the host membrane as part of their mode of action. However, the vital role of specific virulence-associated lipids in modulating cellular functions by altering the host membrane organization and associated signaling pathways remain unanswered questions. Here, we combined chemical synthesis, biophysics, cell biology, and molecular dynamics simulations to elucidate host membrane structure modifications and modulation of membrane-associated signaling using synthetic Mycobacterium tuberculosis sulfoglycolipids (Mtb SL). We reveal that Mtb SL reorganizes the host cell plasma membrane domains while showing higher preference for fluid membrane regions. This rearrangement is governed by the distinct conformational states sampled by SL acyl chains. Physicochemical assays with SL analogues reveal insights into their structure-function relationships, highlighting specific roles of lipid acyl chains and headgroup, along with effects on autophagy and cytokine profiles. Our findings uncover a mechanism whereby Mtb uses specific chemical moieties on its lipids to fine-tune host lipid interactions and confer control of the downstream functions by modifying the cell membrane structure and function. These findings will inspire development of chemotherapeutics against Mtb by counteracting their effects on the host-cell membrane.

Syntheses of the 6'- N-(2-hydroxyethyl) and 1- N-(4-amino-2 S-hydroxybutyryl) derivatives of the 4,6-aminoglycoside sisomicin and that of the doubly modified 1- N-(4-amino-2 S-hydroxybutyryl)-6'- N-(2-hydroxyethyl) derivative known as plazomicin are reported together with their antibacterial and antiribosomal activities and selectivities. The 6'- N-(2-hydroxyethyl) modification results in a moderate increase in prokaryotic/eukaryotic ribosomal selectivity, whereas the 1- N-(4-amino-2 S-hydroxybutyryl) modification has the opposite effect. When combined in plazomicin, the effects of the two groups on ribosomal selectivity cancel each other out, leading to the prediction that plazomicin will exhibit ototoxicity comparable to those of the parent and the current clinical aminoglycoside antibiotics gentamicin and tobramycin, as borne out by ex vivo studies with mouse cochlear explants. The 6'- N-(2-hydroxyethyl) modification restores antibacterial activity in the presence of the AAC(6') aminoglycoside-modifying enzymes, while the 1- N-(4-amino-2 S-hydroxybutyryl) modification overcomes resistance to the AAC(2') class but is still affected to some extent by the AAC(3) class. Neither modification is able to circumvent the ArmA ribosomal methyltransferase-induced aminoglycoside resistance. The use of phenyltriazenyl protection for the secondary amino group of sisomicin facilitates the synthesis of each derivative and their characterization through the provision of sharp NMR spectra for all intermediates.

The adamantanyl thioglycosides of 5-isothiocyano and 5-azido 5-desamino-4,7,8,9-tetra-O-acetylneuraminic acid methyl ester were converted into the corresponding dibutyl phosphates, which proved to be excellent α-selective donors for O-sialidation with a range of typical acceptors, and good donors for reaction with allyltributylstannane, albeit without significant anomeric selectivity. In the KDN series the dibuylphosphate derived from a donor carrying a 4,5-cyclic carbonate protecting group afforded the corresponding C-glycoside with excellent α-selectivity on activation in the presence of allyltributylstannane, whereas the corresponding donor carrying acetate esters at the 4- and 5-positions was unselective. Overall, it is revealed that while the strongly electron-withdrawing isothiocyanato and azido groups are sufficient to promote highly α-selective O-sialidation, they are inadequate when faced with less reactive nucleophiles when mixtures of anomers are obtained.

Fungal glycolipids emmyguyacins A and B inhibit the pH-dependent conformational change of hemaglutinin A during replication of the Influenza virus. Herein, we report the first total synthesis and structure confirmation of emmyguyacins A and B. Our efficient route, which involves regioselective functionalization of trehalose, allows rapid access to adequate amounts of chemically pure emmyguyacin analogues including the desoxylate derivatives for SAR studies.

A novel methodology for the regioselective O6 acylation of the 2,3-diaryl trehaloses to access Mycobacterium tuberculosis sulfolipid SL-3 and related 2,3,6-triester glycolipid analogues is reported for the first time. The methodology was successfully extended to achieve the first total synthesis of the tetraacylated trehalose glycolipid from Mycobacterium paraffinicum. The corresponding 2,3,6'-triesters trehalose glycolipids were also synthesized starting from the common 2,3-diacyl trehalose. These synthetic glycolipids are potential candidates for serodiagnosis and vaccine development for tuberculosis.

Total synthesis of three important trehalose containing tetra-saccharides isolated from Mycobacterium smegmatis is reported for the first time, using regioselective opening of benzylidene acetals and stereoselective glycosylations as key steps. The 1,2-cis stereoselectivity in the glycosylation reactions was achieved using anchimeric assistance from a remote participating group, steric effects and solvent participation. The synthetic strategy can also be utilized for the assembly of structurally related oligosaccharides from M. tuberculosis.

The first synthesis of maradolipid, a unique dissymmetrically 6,6'-di-O-acylated trehalose glycolipid isolated from C. elegans, is accomplished in five steps starting from trehalose in 45% overall yield. The short synthesis relies on dissymmetrization of trehalose core via regioselective acylation of a 2,3,4,2',3',4'-hexa-O-TMS trehalose 6,6'-diol derivative as a key step.