New Chirally Modified Bisphosphonates for Synthesis of Individual Beta,Gamma-CHX-Deoxynucleotide Diastereomers

Uridine Bisphosphonates Differentiate Phosphoglycosyl Transferase Superfamilies

Complex bacterial glycoconjugates drive interactions between pathogens, symbionts, and their human hosts. Glycoconjugate biosynthesis is initiated at the membrane interface by phosphoglycosyl transferases (PGTs), which catalyze the transfer of a phosphosugar from a soluble uridine diphosphosugar (UDP-sugar) substrate to a membrane-bound polyprenol-phosphate (Pren-P). The two distinct superfamilies of PGT enzymes (polytopic and monotopic) show striking differences in their structure and mechanism. We designed and synthesized a series of uridine bisphosphonates (UBPs), wherein the diphosphate of the UDP and UDP-sugar is replaced by a substituted methylene bisphosphonate (CXY-BPs; X/Y = F/F, Cl/Cl, (S)-H/F, (R)-H/F, H/H, CH3/CH3). UBPs and UBPs incorporating an N-acetylglucosamine (GlcNAc) substituent at the β-phosphonate were evaluated as inhibitors of a polytopic PGT (WecA from Thermotoga maritima) and a monotopic PGT (PglC from Campylobacter jejuni). Although CHF-BP most closely mimics diphosphate with respect to its acid/base properties, the less basic CF2-BP conjugate more strongly inhibited PglC, whereas the more basic CH2-BP analogue was the strongest inhibitor of WecA. These surprising differences indicate different modes of ligand binding for the different PGT superfamilies, implicating a modified P-O- interaction with the structural Mg2+. For the monoPGT enzyme, the two diastereomeric CHF-BP conjugates, which feature a chiral center at the Pα-CHF-Pβ carbon, also exhibited strikingly different binding affinities and the inclusion of GlcNAc with the native α-anomer configuration significantly improved binding affinity. UBP-sugars are thus revealed as informative new mechanistic probes of PGTs that may aid development of novel antibiotic agents for the exclusively prokaryotic monoPGT superfamily.

Uridine Bisphosphonates Differentiate Phosphoglycosyl Transferase Superfamilies

Complex bacterial glycoconjugates are essential for bacterial survival, and drive interactions between pathogens and symbionts, and their human hosts. Glycoconjugate biosynthesis is initiated at the membrane interface by phosphoglycosyl transferases (PGTs), which catalyze the transfer of a phosphosugar from a soluble uridine diphospho-sugar (UDP-sugar) substrate to a membrane-bound polyprenol-phosphate (Pren-P). Two distinct superfamilies of PGT enzymes, denoted as polytopic and monotopic, carry out this reaction but show striking differences in structure and mechanism. With the goal of creating non-hydrolyzable mimics (UBP-sugars) of the UDP-sugar substrates as chemical probes to interrogate critical aspects of these essential enzymes, we designed and synthesized a series of uridine bisphosphonates (UBPs), wherein the diphosphate bridging oxygen of the UDP and UDP-sugar is replaced by a substituted methylene group (CXY; X/Y = F/F, Cl/Cl, (S)-H/F, (R)-H/F, H/H, CH3/CH3). These compounds, which incorporated as the conjugating sugar an N-acetylglucosamine (GlcNAc) substituent at the β-phosphonate, were evaluated as inhibitors of a representative polytopic PGT (WecA from Thermotoga maritima) and a monotopic PGT (PglC from Campylobacter jejuni). Although CHF-BP most closely mimics pyrophosphate with respect to its acid/base properties, the less basic CF2-BP conjugate most strongly inhibited PglC, whereas the more basic CH2-BP analogue was the strongest inhibitor of WecA. These surprising differences indicate different modes of ligand binding for the different PGT superfamilies implicating a modified P-O- interaction with the structural Mg2+, consistent with their catalytic divergence. Furthermore, at least for the monoPGT superfamily example, this was not the sole determinant of ligand binding: the two diastereomeric CHF-BP conjugates, which feature a chiral center at the Pα-CHF-Pβ carbon, exhibited strikingly different binding affinities and the inclusion of GlcNAc with the native α-anomer configuration significantly improved binding affinity. UBP-sugars are a valuable tool for elucidating the structures and mechanisms of the distinct PGT superfamilies and offer a promising scaffold to develop novel antibiotic agents for the exclusively prokaryotic monoPGT superfamily.

Rapid Entry into Biologically Relevant α,α-Difluoroalkylphosphonates Bearing Allyl Protection-Deblocking under Ru(II)/(IV)-Catalysis

A convenient synthetic route to α,α-difluoroalkylphosphonates is described. Structurally diverse aldehydes are condensed with LiF2CP(O)(OCH2CH═CH2)2. The resultant alcohols are captured as the pentafluorophenyl thionocarbonates and efficiently deoxygenated with HSnBu3, BEt3, and O2, and then smoothly deblocked with CpRu(IV)(π-allyl)quinoline-2-carboxylate (1-2 mol %) in methanol as an allyl cation scavenger. These mild deprotection conditions provide access to free α,α-difluoroalkylphosphonates in nearly quantitative yield. This methodology is used to rapidly construct new bis-α,α-difluoroalkyl phosphonate inhibitors of PTPIB (protein phosphotyrosine phosphatase-1B).