Determination of Enantiomeric Excess and Diastereomeric Excess via Optical Methods. Application to α-methyl-ß-hydroxy-carboxylic acids.

Characterization of chiral molecules in solution is paramount for measuring reaction success. However, techniques to distinguish between chiral molecules containing more than one stereocenter through the use of optical techniques remains a challenge. Herein, we report a techique using a series of circular dichroism spectra to train multivariate regression models that are capable of predicting the complete speciation of 3-hydroxy-2-methylbutanoic acid stereoisomers. From this, it is possible to rapidly and accurately determine the enantiomeric excess and diastereomeric excess of the solution without the need for chiral chromatography.

Molecular Encryption and Steganography Using Mixtures of Simultaneously Sequenced, Sequence-Defined Oligourethanes.

Molecular encoding in abiotic sequence-defined polymers (SDPs) has recently emerged as a versatile platform for information and data storage. However, the storage capacity of these sequence-defined polymers remains underwhelming compared to that of the information storing biopolymer DNA. In an effort to increase their information storage capacity, herein we describe the synthesis and simultaneous sequencing of eight sequence-defined 10-mer oligourethanes. Importantly, we demonstrate the use of different isotope labels, such as halogen tags, as a tool to deconvolute the complex sequence information found within a heterogeneous mixture of at least 96 unique molecules, with as little as four micromoles of total material. In doing so, relatively high-capacity data storage was achieved: 256 bits in this example, the most information stored in a single sample of abiotic SDPs without the use of long strands. Within the sequence information, a 256-bit cipher key was stored and retrieved. The key was used to encrypt and decrypt a plain text document containing The Wonderful Wizard of Oz. To validate this platform as a medium of molecular steganography and cryptography, the cipher key was hidden in the ink of a personal letter, mailed to a third party, extracted, sequenced, and deciphered successfully in the first try, thereby revealing the encrypted document.

High-throughput screening of α-chiral-primary amines to determine yield and enantiomeric excess.

A novel screening protocol was developed using a combination of a fluorescent indicator displacement assay and a circular dichroism (CD) active Fe(II) complex to determine concentration and enantiomeric excess (ee) of α-chiral amines, respectively. The analyte concentration is quantified with a pre-formed non-fluorescent imine, where transimination with the chiral amine results in displacement of the fluorophore 2-naphthylamine. After discerning the concentration of amine via fluorescence in a wellplate reader, the analyte is then incorporated into a three-component octahedral Fe(II) assembly for ee determination using an EKKO CD plate-reader. With these two assays, both the ee and yield of asymmetric transformations of 192 samples could be determined with acceptable errors in under fifteen minutes (not counting the preparation time). This combined speed and accuracy provides an attractive solution to overcoming analytical bottlenecks when creating α-chiral amines.

Efficient molecular encoding in multifunctional self-immolative urethanes.

Molecular encoding in sequence-defined polymers shows promise as a new paradigm for data storage. Here, we report what is, to our knowledge, the first use of self-immolative oligourethanes for storing and reading encoded information. As a proof of principle, we describe how a text passage from Jane Austen's Mansfield Park was encoded in sequence-defined oligourethanes and reconstructed via self-immolative sequencing. We develop Mol.E-coder, a software tool that uses a Huffman encoding scheme to convert the character table to hexadecimal. The oligourethanes are then generated by a high-throughput parallel synthesis. Sequencing of the oligourethanes by self-immolation is done concurrently in a parallel fashion, and the liquid chromatography-mass spectrometry (LC-MS) information decoded by our Mol.E-decoder software. The passage is capable of being reproduced wholly intact by a third-party, without any purifications or the use of tandem MS (MS/MS), despite multiple rounds of compression, encoding, and synthesis.

"Benchtop" Biaryl Coupling Using Pd/Cu Cocatalysis: Application to the Synthesis of Conjugated Polymers.

Typically, Suzuki couplings used in polymerizations are performed at raised temperatures in inert atmospheres. As a result, the synthesis of aromatic materials that utilize this chemistry often demands expensive and specialized equipment on an industrial scale. Herein, we describe a bimetallic methodology that exploits the distinct reactivities of palladium and copper to perform high yielding aryl-aryl dimerizations and polymerizations that can be performed on a benchtop under ambient conditions. These couplings are facile and can be performed by simple mixing in the open vessel. To demonstrate the utility of this method in the context of polymer synthesis: polyfluorene, polycarbazole, polysilafluorene, and poly(6,12-dihydro-dithienoindacenodithiophene) were created at ambient temperature and open to air.

Next-Generation TLC: A Quantitative Platform for Parallel Spotting and Imaging.

A high-throughput screening approach for simultaneous analysis and quantification of the percent conversion of up to 48 reactions has been developed using a thin-layer chromatography (TLC) imaging method. As a test-bed reaction, we monitored 48 thiol conjugate additions to a Meldrum's acid derivative (1) in parallel using TLC. The TLC elutions were imaged using a cell phone and a LEGO brick-constructed UV/vis light box. Further, a spotting device was constructed from LEGO bricks that allows simple transfer of the samples from a well-plate to the TLC plate. Using software that was developed to detect "blobs" and report their intensity, we were able to quantitatively determine the extent of completion of the 48 reactions with one analysis.

Sequencing of Sequence-Defined Oligourethanes via Controlled Self-Immolation.

Sequence-defined polymers show promise for biomimetics, self-assembly, catalysis, and information storage, wherein the primary structure begets complex chemical processes. Here we report the solution-phase and the high-yielding solid-phase syntheses of discrete oligourethanes and methods for their self-immolative sequencing, resulting in rapid and robust characterization of this class of oligomers and polymers, without the use of MS/MS. Crucial to the sequencing is the inherent reactivity of the terminal alcohol to "unzip" the oligomers, in a controlled and iterative fashion, releasing each monomer as a 2-oxazolidinone. By monitoring the self-immolation reaction via LC/MS, an applied algorithm rapidly produces the sequence of the oligourethane. Not only does this process provide characterization of structurally complex molecules, it works as a reader of molecular information.

Rapid Optical Determination of Enantiomeric Excess, Diastereomeric Excess, and Total Concentration Using Dynamic-Covalent Assemblies: A Demonstration Using 2-Aminocyclohexanol and Chemometrics.

Optical analysis of reaction parameters such as enantiomeric excess (ee), diastereomeric excess (de), and yield are becoming increasingly useful as assays for differing functional groups become available. These assays typically exploit reversible covalent or noncovalent assemblies that impart optical signals, commonly circular dichroism (CD), that are indicative of the stereochemistry and ee at a stereocenter proximal to the functional group of interest. Very few assays have been reported that determine ee and de when two stereocenters are present, and none have targeted two different functional groups that are vicinal and lack chromophores entirely. Using a CD assay that targets chiral secondary alcohols, a separate CD assay for chiral primary amines, a UV-vis assay for de, and a fluorescence assay for concentration, we demonstrate a work-flow for speciation of the enantiomers and diastereomers of 2-aminocyclohexanol as a test-bed analyte. Because of the fact the functional groups are vicinal, we found that the ee determination at the two stereocenters is influenced by the adjacent center, and this led us to implement a chemometric patterning approach, resulting in a 4% absolute error in full speciation of the four stereoisomers. The procedure presented herein would allow for the total speciation of around 96 reactions in 27 min using a high-throughput experimentation routine. While 2-aminocyclohexanol is used to demonstrate the methods, the general workflow should be amenable to analysis of other stereoisomers when two stereocenters are present.

Mathematical Relationships of Individual Stereocenter er Values to dr Values.

A mathematical relationship is derived for relating the enantiomeric ratios (er values) of two individual stereocenters within a single chiral molecule to the diastereomeric ratio (dr). Whereas the er (or enantiomeric excess, ee) of chiral molecules is readily determined by chiral chromatography and dr values can be determined by chromatography or NMR, modern methods for the optical determination of er values at individual functional groups do not normally determine the er and dr of the entire molecule. We find there is only a special circumstance when knowledge of the er of two individual stereocenters can be used to predict the er of the enantiomers in each diastereomeric set, along with the dr of the stereoisomers. Under circumstances where this relationship fails, one will require a dr assay in addition to two individual er assays to fully characterize the stereochemical parameters of a reaction. Thus, with these circumstances in mind, we give mathematical relationships for determining complete stereoisomer speciation having the knowledge of individual stereocenter er values and a dr value.