Amino-BChept-5-ene-COOH(R,R,S,S/S,S,R,R)

Upon development of a workflow to analyze (±)-Verapamil and its metabolites using differential mobility spectrometry (DMS), we noticed that the ionogram of protonated Verapamil consisted of two peaks. This was inconsistent with its metabolites, as each exhibited only a single peak in the respective ionograms. The unique behaviour of Verapamil was attributed to protonation at its tertiary amino moiety, which generated a stereogenic quaternary amine. The introduction of additional chirality upon N-protonation of Verapamil renders four possible stereochemical configurations for the protonated ion: (R,R), (S,S), (R,S), or (S,R). The (R,R)/(S,S) and (R,S)/(S,R) enantiomeric pairs are diastereomeric and thus exhibit unique conformations that are resolvable by linear and differential ion mobility techniques. Protonation-induced chirality appears to be a general phenomenon, as N-protonation of 12 additional chiral amines generated diastereomers that were readily resolved by DMS.

Synthetic monorhamnolipids differ from biologically produced material because they are produced as single congeners, depending on the β-hydroxyalkanoic acid used during synthesis. Each congener is produced as one of four possible diastereomers resulting from two chiral centers at the carbinols of the lipid tails [(R,R), (R,S), (S,R) and (S,S)]. We compare the biodegradability (CO2 respirometry), acute toxicity (Microtox assay), embryo toxicity (Zebrafish assay), and cytotoxicity (xCELLigence and MTS assays) of synthetic rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-C10-C10) monorhamnolipids against biosynthesized monorhamnolipid mixtures (bio-mRL). All Rha-C10-C10 diastereomers and bio-mRL were inherently biodegradable ranging from 34 to 92% mineralized. The Microtox assay showed all Rha-C10-C10 diastereomers and bio-mRL are slightly toxic according to the US EPA ecotoxicity categories with 5 min EC50 values ranging from 39.6 to 87.5 μM. The zebrafish assay showed that of 22 developmental endpoints tested, only mortality was observed at 120 h post fertilization; all Rha-C10-C10 diastereomers and bio-mRL caused significant mortality at 640 μM, except the Rha-C10-C10 (R,R) which showed no developmental effects. xCELLigence and MTS showed IC50 values ranging from 103.4 to 191.1 μM for human lung cell line H1299 after 72 h exposure. These data provide key information regarding Rha-C10-C10 diastereomers that is pertinent when considering potential applications.

An in-depth biodegradation test program was executed on the hexadentate ligand Ethylene Diamine Di Succinate (EDDS). The EDDS structure contains two chiral carbon atoms, and has three stereoisomers ([R,R], [R,S]/[S,R], [S,S]). Our research has focused on the isomer mixture (i.e. 25%[S,S]; 25%[R,R]; 50%[S,R]/[R,S], as produced from the reaction of ethylene diamine with maleic anhydride) and on the single [S,S]- and [R,R]-isomers. Biodegradation screening of the 14C-labelled EDDS isomer mixture in a Batch Activated Sludge (BAS) test with various inocula revealed incomplete mineralization, up to ca. 65% after 28 days. N-(2-aminoethyl) aspartic acid (AEAA), probably the d-isomer, was identified as the major portion of the 14C-material remaining in solution. Further testing revealed that the [S,S]-isomer is rapidly and completely mineralized in all test systems. By contrast, [R,R]-EDDS remained undegraded in a Sturm (OECD 301B) test, but was very slowly biotransformed into the recalcitrant metabolite AEAA in a BAS test. The [S,R]/[R,S] form undergoes biotransformation to AEAA in both high and low biomass systems. In a sewage treatment simulation test (OECD 303) the steady state DOC removal of mixture-EDDS in a CAS test was limited to 25-35%, even after extensive pre-acclimation, while the [S,S]-isomer achieved nearly complete removal (96%). This study illustrates the importance stereospecificity may have on the biodegradation and metabolite formation of a chemical. A biodegradation scheme for the different EDDS stereoisomers is proposed.