Stereocontrolled Total Synthesis of Muraymycin D1 Having a Dual Mode of Action against Mycobacterium tuberculosis

Abstract

A stereocontrolled first total synthesis of muraymycin D1 (1) has been achieved. The synthetic route is highly stereoselective, featuring 1) selective β-ribosylation of the C2-methylated amino ribose, 2) selective Strecker reaction, 3) ring-opening reaction of a diastereomeric mixture of a diaminolactone to synthesize muraymycidine (epi-capreomycidine). The acid-cleavable protecting groups for secondary alcohol and uridine ureido nitrogen are applied for simultaneous deprotections with the Boc and tBu groups. Muraymycin D1 (1) and its amide derivatives (2 and 3) exhibited growth inhibitory activity against Mycobacterium tuberculosis (MIC50 1.56–6.25 μg/mL) and strong enzyme inhibitory activities against the bacterial phosphotransferases (MurX and WecA) (IC50 0.096−0.69 μM).

Insights into the Target Interaction of Naturally Occurring Muraymycin Nucleoside Antibiotics

“…[10] Further insights into the biological action of muraymycins were recently obtained from the X-ray co-crystal structure of MraY from Aquifex aeolicus in complex with the natural product muraymycin D2. [11] In many of the aforementioned SAR investigations on muraymycin analogues, biological potencies were mainly evaluated on the basis of antibacterial activities (i.e., minimal inhibitory concentrations (MIC)).…”

“…Such an approach has only been pursued for some of the previously reported muraymycin analogues. [10] Remarkably, even information on the MraY-inhibiting properties of the parent natural products is scarce. The originally isolated, naturally occurring muraymycins were solely assessed by their inhibition of the formation of lipid II (i.e., the biosynthetic intermediate following lipid I 2 ) and peptidoglycan in coupled assays, thus only indirectly supporting MraY inhibition.…”

“…All isolated natural products 3 – 8 were initially tested for their inhibitory potency towards two different preparations of MraY: (i) MraY from S. aureus , overexpressed in E. coli and used as crude membranes from overexpressing cells; [5a,10f,12d] and (ii) MraY from Aquifex aeolicus , overexpressed in E. coli and purified to homogeneity in the presence of a non-denaturing detergent (modified protocol from ref. [6b,11a] ).…”

“…Activity assays were performed in triplicates, providing (after data fitting) IC 50 values for inhibition with standard deviations (Table 1). We had previously reported the synthetic 5′-defunctionalized (i.e., 5′-deoxy) muraymycin analogue 9 (Table 1), [10f] which was also included in this study.…”

“…This finding supports a previous hypothesis that the fatty acyl unit might instead contribute primarily to the cellular uptake rather than target interaction. [10d,13] On the other hand, muraymycin D1 7 was a ca. 30-fold less active MraY inhibitor than C1 6 , although it only differs in the missing β-hydroxy group in the leucine moiety.…”