Total synthesis of mycolic acids and site-selective functionalization of aminoglycoside antibiotics

It is estimated that roughly a quarter of the world population is infected by Tuberculosis (TB), either by a latent or active form. TB can be treated by subjecting the patient to a dedicated antibiotic regimen. However, as a result of the rising multi-drug resistant (MDR-TB) and extensively multi-drug resistant (XDR-TB) tuberculosis forms, the commonly used antibiotics are losing their effectiveness. The treatment is further complicated by M. tuberculosis’ unusually fortified cell wall, which consists of a high abundance of mycolic acids in the outer layer. These mycolic acids are essential for the survival of pathogenic TB bacteria, and are partially responsible for the immune response upon infection. Although the chemical structure of mycolic acids has been elucidated, their full stereochemical arrangement (i.e. the precise arrangement of atoms in 3D space) is yet to be determined. The tuberculosis field is developing vaccine candidates and diagnostic kits based on mycolic acids, but is reluctant doing so based on natural material, because of potential contamination and the cumbersome culturing of pathogenic M. tuberculosis. Therefore, the tuberculosis field would gain considerable progress with the complete determination of the stereochemistry, and a high yielding chemical synthesis of mycolic acids. During my PhD, I prepared these mycolic acids by chemical synthesis. These synthetic molecules will allow for future biological studies, and aid in the determination of the stereochemistry. In addition, I also prepared novel (aminoglycoside) antibiotics, which potentially could lead to useful antibiotics. Future tests will be needed to determine their effectiveness

A Current Overview of Two Viroids Prevailing in Citrus Orchards: Citrus Exocortis Viroid and Hop Stunt Viroid

Citrus exocortis viroid (CEVd) and hop stunt viroid (HSVd) are the main viroids circulating in all citrus-growing areas worldwide, and causing two well-known diseases on citrus trees; exocortis and cachexia, respectively. These viroids are small, covalently closed single-stranded RNA, allocated to the Pospiviroidae family. CEVd is the first viroid being described on citrus trees in 1948 in California. It is considered the largest citrus viroid at 371 nucleotides. It causes bark scaling disorder on the rootstock of citrus trees grafted on trifoliate orange and its hybrids and can cause dwarfing of trees grown on these rootstocks. HSVd was first observed in 1945 in Florida. It consists of 299 nucleotides. Stunting, chlorosis, bark gumming, stem pitting, decline, and depressions in the wood are the main symptoms of HSVd in mandarin and its hybrids. The introduction and propagation of infected budwoods are the main causes of viroids spread in citrus orchards. These agents are mechanically sap-transmissible and spread by contaminated tools. Neither seed transmission nor vectors have been reported for both viroids. Root transmission, though possible, would be overshadowed by mechanical transmission. Rapid and sensitive molecular-based detection methods specific to both viroids are available. Both diseases are controlled by using viroids-free budwoods for new plantations, launching budwood certification programs, and establishing a quarantine system for new citrus varieties introduction. The most important achievements in CEVd and HSVd researches are outlined in this chapter. This would help to provide a clearer understanding of the diseases they cause and contribute to the development of better control strategies

Total Synthesis of a Mycolic Acid from Mycobacterium tuberculosis

In Mycobacterium tuberculosis, mycolic acids and their glycerol, glucose, and trehalose esters ("cord factor") form the main part of the mycomembrane. Despite their first isolation almost a century ago, full stereochemical evaluation is lacking, as is a scalable synthesis required for accurate immunological, including vaccination, studies. Herein, we report an efficient, convergent, gram-scale synthesis of four stereo-isomers of a mycolic acid and its glucose ester. Binding to the antigen presenting protein CD1b and T cell activation studies are used to confirm the antigenicity of the synthetic material. The absolute stereochemistry of the syn-methoxy methyl moiety in natural material is evaluated by comparing its optical rotation with that of synthetic material

Stereoselective Protection-Free Modification of 3-Keto-saccharides

Unprotected 3-keto-saccharides have become readily accessible via site-selective oxidation, but their protection-free functionalization is relatively unexplored. Here we show that protecting groups are obsolete in a variety of stereoselective modifications of our model substrate methyl α-glucopyranoside. This allows the preparation of rare sugars and the installation of click handles and reactive groups. To showcase the applicability of the methodology, maltoheptaose has been converted into a chemical probe, and the rare sugar evalose has been synthesized

ATR-FTIR spectroscopy combined with DNA barcoding and GC-MS to assess the quality and purity of saffron (Crocus Sativus L.)

peer reviewedFourier transform infrared spectra of saffron (Crocus sativus L.) samples were acquired using attenuated total reflectance (ATR-FTIR). The main objective of the study was to determine the chemical composition of 11 samples of saffron collected from different areas in Morocco using the chemometric analysis of ATR-FTIR fingerprints and identifying the adulterated saffron among samples bought from local markets in different countries (Spain, Iran, and Morocco). The the authenticity and the purity of saffron samples was validated through a molecular analysis (DNA barcoding coupled to sequencing) and chromatographic analysis GC-MS. The results of ATR-FTIR showed vibration intensities of six distinct fingerprint regions displaying statistically significant differences. The spectrum of the sample from Timjicht (Taznakht) showed typical bands due to the vibration in 3000-2800 cm-1 (the richest in carbohydrates, lipids, and amino acids) and 1800 to 1725 cm-1 region (the richest in carbonyl and ester groups) and was classified a single subset in samples scatter plot. Then samples from Boulmane (S2), Ain Leuh (S3), Taliouine (S6), and Taznakht (S7-S8) were classified close to each other, which indicates the similarity in their vibration intensities mainly in the region of carbohydrates, lipids, amino acids, and esters. Similarities in terms of proteins and hydroxyl groups were revealed between the samples from El Mers (S11) and Taliouine (S1). Finally, the last subgroup contained samples from Ourika, Azilal and Ain Atia, which showed low composition in all components. Furthermore, to detect adulterated saffron from samples of unknown origin, a comparison of the ATR-FTIR spectra were carried out with spectra of pure saffron and results Journal Pre-proof 2 showed that the peaks at 1706, 1732, and 1225 cm-1 (linked to crocin which are present primarily in saffron) were absent in one sample (SI). Interestingly, the use of another plant species named Arrhenatherum elatius as materiel for saffron adulteration was confirmed by the molecular study (DNA barcoding) and chromatographic analysis GC-M

Viruses of cucurbit crops: current status in the Mediterranean Region

peer reviewedCucurbits are among the most cultivated crops, and the most economically important species are melon (Cucumis melo L.), cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thumb.), squash (Cucurbita pepo L.), and pumpkin (Cucurbita spp.). These crops have become important income sources providing export and local consumption commodities in many Mediterranean countries. Increased area of cucurbits has led to the emergence of several viral diseases, which can have impacts on crop production and threaten agricultural sustainability. An overview of the most damaging cucurbit viruses in the Mediterranean area is provided to improve understanding of the diseases they cause and to emphasize effective disease management strategies. An updating of the geographical distribution of these viruses, the symptoms they cause and their means of transmission is also provided. Disease management methods and measures by farmers and phytosanitary authorities to address the virus outbreaks are outlined, including diagnostics, use of tolerant cultivars, and chemical and biological vector control. Mediterranean region farmers have learned many lessons from the damaging pandemics caused by cucurbit viruses, through the extensive published research, and this review provides a basis for managing future outbreaks of newly emerging virus infections

Late-Stage Modification of Aminoglycoside Antibiotics Overcomes Bacterial Resistance Mediated by APH(3') Kinases

The continuous emergence of antimicrobial resistance is causing a threat to patients infected by multidrug‐resistant pathogens. In particular, the clinical use of aminoglycoside antibiotics, broad‐spectrum antibacterials of last resort, is limited due to rising bacterial resistance. One of the major resistance mechanisms in Gram‐positive and Gram‐negative bacteria is phosphorylation of these amino sugars at the 3’‐position by O‐phosphotransferases [APH(3’)s]. Structural alteration of these antibiotics at the 3’‐position would be an obvious strategy to tackle this resistance mechanism. However, the access to such derivatives requires cumbersome multi‐step synthesis, which is not appealing for pharma industry in this low‐return‐on‐investment market. To overcome this obstacle and combat bacterial resistance mediated by APH(3’)s, we introduce a novel regioselective modification of aminoglycosides in the 3’‐position via palladium‐catalyzed oxidation. To underline the effectiveness of our method for structural modification of aminoglycosides, we have developed two novel antibiotic candidates overcoming APH(3’)s‐mediated resistance employing only four synthetic steps

T Cells Specific for a Mycobacterial Glycolipid Expand after Intravenous Bacillus Calmette-Guérin Vaccination

Intradermal vaccination with Mycobacterium bovis bacillus Calmette-Guérin (BCG) protects infants from disseminated tuberculosis, and i.v. BCG protects nonhuman primates (NHP) against pulmonary and extrapulmonary tuberculosis. In humans and NHP, protection is thought to be mediated by T cells, which typically recognize bacterial peptide Ags bound to MHC proteins. However, during vertebrate evolution, T cells acquired the capacity to recognize lipid Ags bound to CD1a, CD1b, and CD1c proteins expressed on APCs. It is unknown whether BCG induces T cell immunity to mycobacterial lipids and whether CD1-restricted T cells are resident in the lung. In this study, we developed and validated Macaca mulatta (Mamu) CD1b and CD1c tetramers to probe ex vivo phenotypes and functions of T cells specific for glucose monomycolate (GMM), an immunodominant mycobacterial lipid Ag. We discovered that CD1b and CD1c present GMM to T cells in both humans and NHP. We show that GMM-specific T cells are expanded in rhesus macaque blood 4 wk after i.v. BCG, which has been shown to protect NHP with near-sterilizing efficacy upon M. tuberculosis challenge. After vaccination, these T cells are detected at high frequency within bronchoalveolar fluid and express CD69 and CD103, markers associated with resident memory T cells. Thus, our data expand the repertoire of T cells known to be induced by whole cell mycobacterial vaccines, such as BCG, and show that lipid Ag-specific T cells are resident in the lungs, where they may contribute to protective immunity