Enhancing the therapeutic window for Spectinamide anti-tuberculosis Agents: Synthesis, Evaluation, and activation of phosphate prodrug 3408.

Spectinamides are a novel class of narrow-spectrum antitubercular agents with the potential to treat drug-resistant tuberculosis infections. Spectinamide 1810 has shown a good safety record following subcutaneous injection in mice or infusion in rats but exhibits transient acute toxicity following bolus administration in either species. To improve the therapeutic index of 1810, an injectable prodrug strategy was explored. The injectable phosphate prodrug 3408 has a superior maximum tolerated dose compared to 1810 or Gentamicin. Following intravenous administration in rodents, prodrug 3408 was quickly converted to 1810. The resulting 1810 exposure and pharmacokinetic profile after 3408 administration was identical to equivalent molar amounts of 1810 given directly by intravenous administration. 3408 and the parent 1810 exhibited similar overall efficacy in a BALB/c acute tuberculosis efficacy model. Delivery of 1810 in phosphate prodrug form, therefore, holds the potential to improve further the therapeutic index of an already promising tuberculosis antibiotic.

Synthesis and antibacterial action of 3',6'-disubstituted spectinomycins.

Spectinomycin is an aminocyclitol antibiotic with a unique ribosomal binding site. Prior synthetic modifications of spectinomycin have enhanced potency and antibacterial spectrum through addition at the 6'-position to produce trospectomycin and to the 3'-position to produce spectinamides and aminomethyl spectinomycins. This study focused on the design, synthesis, and evaluation of three 3',6'-disubstituted spectinomycin analogs: trospectinamide, N-benzyl linked aminomethyl, and N-ethylene linked aminomethyl trospectomycins. Computational experiments predicted that these disubstituted analogs would be capable of binding within the SPC ribosomal binding site. The new analogs were synthesized from trospectomycin, adapting the previously established routes for the spectinamide and aminomethyl spectinomycin series. In a cell-free translation assay, the disubstituted analogs showed ribosomal inhibition similar to spectinomycin or trospectomycin. These disubstituted analogs demonstrated inhibitory MIC activity against various bacterial species with the 3'-modification dictating spectrum of activity, leading to improved activity against mycobacterium species. Notably, N-ethylene linked aminomethyl trospectomycins exhibited increased potency against Mycobacterium abscessus and trospectinamide displayed robust activity against M. tuberculosis, aligning with the selective efficacy of spectinamides. The study also found that trospectomycin is susceptible to efflux in M. tuberculosis and M. abscessus. These findings contribute to the understanding of the structure-activity relationship of spectinomycin analogs and can guide the design and synthesis of more effective spectinomycin compounds.

Synthesis of All Stereoisomers of Monomeric Spectomycin A1/A2 and Evaluation of Their Protein SUMOylation-Inhibitory Activity.

A synthetic methodology to access all possible stereoisomers of spectomycin A1 (SMA1) and A2 (SMA2) has been established through late-stage diversification. The key reaction for the construction of all four diastereomers is an intramolecular cyclization based on the umpolung of π-allyl palladium species with bis(pinacolato)diborane (B2 (pin)2 ). Silyl group assisted direct benzylic oxidation of each isomer enabled construction of the fragile ß-hydroxytetralone skeleton to provide the SMAs. The relative and absolute stereochemistry of SMA2 was also determined, and the absolute stereochemistry of SMA1 was extrapolated based on the optical rotation of SMA2. The axial chirality of SMAs is discussed based on circular dichroism spectra and DFT calculations, and it is concluded that the M isomer is predominant in solution. Biochemical assessment of all isomers in vitro revealed that the C9 hydroxyl group and dimeric structure were both important for protein SUMOylation-inhibitory activity.

Aminomethyl spectinomycins as therapeutics for drug-resistant respiratory tract and sexually transmitted bacterial infections.

The antibiotic spectinomycin is a potent inhibitor of bacterial protein synthesis with a unique mechanism of action and an excellent safety index, but it lacks antibacterial activity against most clinically important pathogens. A series of N-benzyl-substituted 3'-(R)-3'-aminomethyl-3'-hydroxy spectinomycins was developed on the basis of a computational analysis of the aminomethyl spectinomycin binding site and structure-guided synthesis. These compounds had ribosomal inhibition values comparable to spectinomycin but showed increased potency against the common respiratory tract pathogens Streptococcus pneumoniae, Haemophilus influenzae, Legionella pneumophila, and Moraxella catarrhalis, as well as the sexually transmitted bacteria Neisseria gonorrhoeae and Chlamydia trachomatis. Non-ribosome-binding 3'-(S) isomers of the lead compounds demonstrated weak inhibitory activity in in vitro protein translation assays and poor antibacterial activity, indicating that the antibacterial activity of the series remains on target against the ribosome. Compounds also demonstrated no mammalian cytotoxicity, improved microsomal stability, and favorable pharmacokinetic properties in rats. The lead compound from the series exhibited excellent chemical stability superior to spectinomycin; no interaction with a panel of human receptors and drug metabolism enzymes, suggesting low potential for adverse reactions or drug-drug interactions in vivo; activity in vitro against a panel of penicillin-, macrolide-, and cephalosporin-resistant S. pneumoniae clinical isolates; and the ability to cure mice of fatal pneumococcal pneumonia and sepsis at a dose of 5 mg/kg. Together, these studies indicate that N-benzyl aminomethyl spectinomycins are suitable for further development to treat drug-resistant respiratory tract and sexually transmitted bacterial infections.

Spectinomycin modification. IV. The synthesis of 3'-aminomethyldihydrospectinomycins via spectinomycin 3'-cyanohydrins.

The C-3'-carbonyl group of N-protected spectinomycin is converted into the corresponding aminomethylalcohols via the intermediacy of cyanohydrins. Methodology for the selective synthesis of either epimer with retention of protection in the aminocyclitol ring provides valuable synthetic intermediates for the preparation of analogs of this important antibiotic. The new methodology provides an efficient synthesis of the highly active 3'-aminomethyldihydrospectinomycins.

Spectinomycin modification. V. The synthesis and biological activity of spectinomycin analogs with ring-expanded sugars.

Tiffeneau-Demjanov rearrangement of 3'-(R)-N,N'-dibenzyloxycarbonyl-3'-aminomethyl-dihydrospectinom ycin results in ring expansion affording the homologous analog with a seven-membered sugar ring. In stark contrast, attempted rearrangement of the 3'-S-isomer leads only to epoxide formation. Deprotection of the ring-expanded homolog gives homospectinomycin. The synthesis and biological activity of this interesting new member of the spectinomycin series and the derived dihydrohomospectinomycin is detailed in this paper.

Modification of spectinomycin. 2. Derivatives of 4-dihydro-4-deoxy-4(R)-aminospectinomycin.

Acyl derivatives 5a approximately j and alkyl derivatives 7a approximately r of 4-dihydro-4-deoxy-4(R)-aminospectinomycin (1a) were prepared and tested for antibacterial activity. Only acyl compounds derived from long chain aliphatic acids showed activity in vitro, but were inactive when tested in vivo. All alkyl derivatives were active in vitro. In vivo however only the short chain derivatives 7a approximately c were active. Compound 7b showed higher activity than spectinomycin.

Studies directed toward the total synthesis of antibiotics: (+)-spectinomycin.

The presence of a dioxaspiro or a fused bicyclic ring system resulting from a diastereoselective intramolecular acetalization of keto diol or keto alcohol units respectively, is a unique structural feature among a number of biologically important natural products. The particular bond arrangement around the ketal carbon atom is, in part, a reflection of the preference for anomeric stereoselection in nature, either at the site of acetalization or in its vicinity. This phenomenon manifests itself in the constitutional structures of several ionophores (polyether type), in the antibiotic spectinomycin as well as other natural products. Synthetic efforts in this area will be discussed, with particular emphasis on spectinomycin as a challenging target.

Spectinomycin modification. IV. 7-deoxy-4(R)-dihydrospectinomycin.

7-Deoxy-4(R)-dihydrospectinomycin (7) has been prepared and its structure firmly established by proton magnetic resonance and high resolution mass spectrometry. This spectinomycin analog is devoid of antibiotic activity.

Spectinomycin modification. I 7-EPI-9-deoxy-4(R)-dihydrospectinomycin.

7-EPI-9-deoxy-4(R)-dihydrospectinomycin (10) had been prepared and its structure firmly established by complete analysis of its pmr spectrum. This analog of spectinomycin is devoid of antibiotic activity.

Spectinomycin modification. II. 7-EPI-sectinomycin.

7-Epi-spectinomycin (9) and 7-epi-4(R)-dihydrospectinomycin (10) have been prepared and their structure firmly established by proton magnetic resonance. Both of these spectinomycin analogs are devoid of antibiotic activity.