Structural and Initial Biological Analysis of Synthetic Arylomycin A₂

Abstract

The growing threat of untreatable bacterial infections has refocused efforts to identify new antibiotics, especially those acting by novel mechanisms. While the inhibition of pathogen proteases has proven to be a successful strategy for drug development, such inhibitors are often limited by toxicity due to their promiscuous inhibition of homologous and mechanistically related human enzymes. Unlike many protease inhibitors, inhibitors of the essential type I bacterial signal peptidase (SPase) may be more specific and thus less toxic due to the enzyme's unique structure and catalytic mechanism. Recently, the arylomycins and related lipoglycopeptide natural products were isolated and shown to inhibit SPase. The core structure of the arylomycins and lipoglycopeptides consists of a biaryl-linked, N-methylated peptide macrocycle attached to a lipopeptide tail, and in the case of the lipoglycopeptides, a deoxymannose moiety. Herein, we report the first total synthesis of a member of this group of antibiotics, arylomycin A2. The synthesis relies on Suzuki-Miyaura-mediated biaryl coupling, which model studies suggested would be more efficient than a lactamization-based route. Biological studies demonstrate that these compounds are promising antibiotics, especially against Gram-positive pathogens, with activity against S. epidermidis that equals that of the currently prescribed antibiotics. Structural and biological studies suggest that both N-methylation and lipidation may contribute to antibiotic activity, whereas glycosylation appears to be generally less critical. Thus, these studies help identify the determinants of the biological activity of arylomycin A2 and should aid in the design of analogs to further explore and develop this novel class of antibiotic.

Pseudomonas aeruginosa Possesses Two Putative Type I Signal Peptidases, LepB and PA1303, Each with Distinct Roles in Physiology and Virulence

“…The carboxy-terminal catalytic domains of Gram-negative SPases are present on the outer surface of the cytoplasmic membrane facing into the periplasm and therefore would be accessible to any inhibitor that could traverse the outer membrane. SPases have been shown to be viable drug targets in other bacteria, with lipoglycopeptides showing antibacterial activity against E. coli and S. pneumoniae while S. epidermidis is sensitive to the related arylomycins (5,31,51). Unfortunately, the type I SPase inhibitors identified to date have not shown antibacterial activity against P. aeruginosa.…”

“…In addition, its natural resistance to many frontline antibiotics is compounded by its genetic capacity to express a wide repertoire of resistance mechanisms and acquisition of additional resistance genes and beneficial mutations (33). The need for a functional SPase for viability has been demonstrated in other organisms, such as E. coli, S. aureus, and Streptococcus pneumoniae (10,13,79), and several inhibitors, including arylomycin and lipoglycopeptide natural products and ␤-lactam analogs (penem inhibitors), have been shown to have activity against SPases (3,5,31,34,37,43,51). In this study, we performed a molecular characterization of the two SPase homologues present within the P. aeruginosa genome, LepB and PA1303, in order to determine their physiological roles and their suitability as drug targets.…”

Broadening the Spectrum of β-Lactam Antibiotics through Inhibition of Signal Peptidase Type I

“…Krisynomycin was isolated from Streptomyces fradiae strain MA7310, and actinocarbasin was isolated from Actinoplanes ferrugineus strain MA7383 (Wilson et al, unpublished). M131 is a synthetic derivative of actinocarbasin that was synthesized by following the approach of Roberts et al (30;Kevin et al,unpublished data). M131(R,Slysine) is an early preparation of M131 consisting of a 1:1 mixture of diastereomers at the lysine stereogenic center, of which the single (S,S,S,S) diastereomer (M131) is more active (4-fold).…”

Type I Signal Peptidase and Protein Secretion inStaphylococcus epidermidis

“…Arylomycin C 16 was synthesized as described previously (47). S. epidermidis RP62A was obtained from the ATCC (ATCC 35984).…”