The Functionalization of Oligonucleotides Via Phosphoramidite Derivatives

Synthesis of 5'-Thiol Functionalized Morpholino Oligo-Nucleotide and Subsequent Conjugation with IGT to Improve Delivery and Antisense Efficacy In Vitro

Thiol functionalized oligonucleotides are useful intermediates for a wide range of applications including DNA nanobiotechnology field through conjugation with various types of probes and cargos. Due to the limitation of synthetic process, phosphorodiamidate morpholino oligonucleotides (PMOs) have not been explored like other oligonucleotides through SH conjugation as mentioned above. In this paper, we report the synthesis of 5'-SH functionalized PMO using a solid support synthesis protocol with an optimized cysteine derived linker so that loading and coupling efficiency of morpholino monomers were effective enough to get a 25-mer 5'-SH functionalized PMO against human Nanog. The PMO with SH functionality was subsequently conjugated with our previously reported Internal Oligo-guanidinium Transporter (IGT) in solution phase to obtain the IGT-PMO conjugate. Interestingly, 5'-conjugated PMO (IGT-PMO) showed 2.5 times better antisense efficacy than 3'-conjugated PMO with IGT (PMO-IGT). 5'-Conjugation enables us to use IGT-PMO for further conjugation at the 3'-N terminal of PMO which was not possible earlier with 5'-OH-PMO-IGT. PMO has become an important class of antisense reagents because four PMO-based drugs have been approved for the treatment of Duchenne muscular dystrophy; hence such an improved result with 5'-modified PMO could be useful for enhancing the therapeutic efficacy of DMD drugs. Similarly, thiol-modified PMO could also be explored like other thiol-containing oligonucleotides for various other applications.

Post-Synthetic Modification of Oligonucleotides Through Oxidative Amination of 4-Thio-2'-Deoxyuridine

Functionalized oligonucleotides (ONs) are widely applied as target recognition molecules for biosensing and gene regulation. Herein, we describe a general method for post-synthetic modification of ONs based on the oxidative amination of 4-thio-2'-deoxyuridine (4SdU) with sodium periodate and several amines. Alkyne-/azide-, biotin-, and fluorophore-modified ONs were prepared by modifying 4SdU-containing ONs with the corresponding amines and characterized for their bioorthogonal reactivity, streptavidin-binding affinity, and fluorescence properties, respectively. We synthesized three fluorophore-modified ONs with and without the aromatic fluorophores conjugated to modified nucleobases and investigated their emission properties. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Post-synthetic modification of ONs Supporting Protocol: Preparation of dansyl ethylenediamine Basic Protocol 2: Quantification of ON reaction yields Basic Protocol 3: Characterization of modified ONs.

Single-molecule junction spontaneously restored by DNA zipper

The electrical properties of DNA have been extensively investigated within the field of molecular electronics. Previous studies on this topic primarily focused on the transport phenomena in the static structure at thermodynamic equilibria. Consequently, the properties of higher-order structures of DNA and their structural changes associated with the design of single-molecule electronic devices have not been fully studied so far. This stems from the limitation that only extremely short DNA is available for electrical measurements, since the single-molecule conductance decreases sharply with the increase in the molecular length. Here, we report a DNA zipper configuration to form a single-molecule junction. The duplex is accommodated in a nanogap between metal electrodes in a configuration where the duplex is perpendicular to the nanogap axis. Electrical measurements reveal that the single-molecule junction of the 90-mer DNA zipper exhibits high conductance due to the delocalized π system. Moreover, we find an attractive self-restoring capability that the single-molecule junction can be repeatedly formed without full structural breakdown even after electrical failure. The DNA zipping strategy presented here provides a basis for novel designs of single-molecule junctions.

The versatility of DNA has inspired many single-molecule investigations utilizing nanotechnology. Harashima et al. have a somewhat different take on the subject and study a zipper configuration bridging electrodes that resembles an active electro-mechanical component instead.

General Method for Post-Synthetic Modification of Oligonucleotides Based on Oxidative Amination of 4-Thio-2'-deoxyuridine

Functionalized oligonucleotides (ONs) are widely applied as target binding molecules for biosensing and regulators for gene expression. Numerous efforts have been focused on developing facile methods for preparing these useful ONs carrying diverse modifications. Herein, we present a general method for postsynthetic modification of ONs via oxidative amination of 4-thio-2'-deoxyuridine (4SdU). 4SdU-containing ON can be derived by both alkyl and aromatic amines. Using this approach, ONs are successfully attached with alkyne/azide, biotin and dansylamide moieties, and these as-prepared ONs possess the expected biorthogonal reactivity, streptavidin affinity and fluorescent property, respectively. Furthermore, we also directly install fluorophores to the ON nucleobase based on oxidative amination of 4SdU, and these fluorophores exhibit distinct luminescence behaviors before and after conjugation. We believe our method will be a versatile strategy for constructing various functionalized ONs used in a wide range of nucleic acid applications.

A novel class of polymeric fluorescent dyes assembled using a DNA synthesizer

In the pursuit of a novel class of fluorescent dyes we have developed a programmable polymer system that enables the rational design and control of macromolecular constructs through simple control of polymer primary sequence. These polymers are assembled using standard phosphoramidite chemistry on a DNA synthesizer which allows for extremely rapid prototyping and enables many permutations due to the large selection of phosphoramidite monomers presently available on the market. This programmability to some extent allows us to control the interactions/spacing of payload molecules distributed along the designed polymeric backbone. Control of molecular architecture using this technology has allowed us to address the long-standing technical issue of contact quenching between fluorescent dyes offering new possibilities in the life sciences arena. Much like peptidic sequences coding for enzymes, cofactors, and receptors (all needing control of tertiary structure for proper function via primary sequence) our programmable system approaches a similar endpoint using a phosphate based polymeric backbone assembled in a completely automated fashion. Using this novel technology, we have efficiently synthesized several types of fluorescent dyes and demonstrated the programmability in molecule design, including the increases in brightness of the fluorescence emission.

The Medicinal Chemistry of RNase H-activating Antisense Oligonucleotides

This review focuses on the properties that an RNase H-activating antisense oligonucleotide (ASO) drug must have to function effectively in animals, as well as on medicinal chemistry strategies to achieve these properties. The biochemistry and structural requirements for activating RNase H are briefly summarized, as well as chemical modifications that can effect activation of RNase H when an ASO is bound to target RNA. The key modifications available to the medicinal chemist to engineer desired properties of the ASO are briefly reviewed, as are ASO design strategies to achieve optimal activity in animal systems. Lastly, the interactions of ASOs with proteins and strategies to control these interactions to improve the profile of ASOs are discussed.

New Generation of Clickable Nucleic Acids: Synthesis and Active Hybridization with DNA

Due to the ability to generate oligomers of precise sequence, sequential and stepwise solid-phase synthesis has been the dominant method of producing DNA and other oligonucleotide analogues. The requirement for a solid support, however, and the physical restrictions of limited surface area thereon significantly diminish the efficiency and scalability of these syntheses, thus, negatively affecting the practical applications of synthetic polynucleotides and other similarly created molecules. By employing the robust photoinitiated thiol-ene click reaction, we developed a new generation of clickable nucleic acids (CNAs) with a polythioether backbone containing repeat units of six atoms, matching the spacing of the phosphodiester backbone of natural DNA. A simple, inexpensive, and scalable route was utilized to produce CNA monomers in gram-scale, which indicates the potential to dramatically lower the cost of these DNA mimics and thereby expand the scope of these materials. The efficiency of this approach was demonstrated by the completion of CNA polymerization in 30 seconds, as characterized by size-exclusive chromatography (SEC) and infrared (IR) spectroscopy. CNA/DNA hybridization was demonstrated by gel electrophoresis and used in CdS nanoparticle assembly.

Fine Tuning of Pyrene Excimer Fluorescence in Molecular Beacons by Alteration of the Monomer Structure

Oligonucleotide probes labeled with pyrene pairs that form excimers have a number of applications in hybridization analysis of nucleic acids. A long excited state lifetime, large Stokes shift, and chemical stability make pyrene excimer an attractive fluorescent label. Here we report synthesis of chiral phosphoramidite building blocks based on (R)-4-amino-2,2-dimethylbutane-1,3-diol, easily available from an inexpensive d-(-)-pantolactone. 1-Pyreneacetamide, 1-pyrenecarboxamide, and DABCYL derivatives have been used in preparation of molecular beacon (MB) probes labeled with one or two pyrenes/quenchers. We observed significant difference in the excimer emission maxima (475-510 nm; Stokes shifts 125-160 nm or 7520-8960 cm^-1) and excimer/monomer ratio (from 0.5 to 5.9) in fluorescence spectra depending on the structure and position of monomers in the pyrene pair. The pyrene excimer formed by two rigid 1-pyrenecarboxamide residues showed the brightest emission. This is consistent with molecular dynamics data on excimer stability. Increase of the excimer fluorescence for MBs after hybridization with DNA was up to 24-fold.

Synthesis of RNA 5'-Azides from 2'-O-Pivaloyloxymethyl-Protected RNAs and Their Reactivity in Azide-Alkyne Cycloaddition Reactions

Commercially available 2'-O-pivaloyloxymethyl (PivOM) phosphoramidites were employed in an SPS protocol for RNA 5' azides. The utility of the N₃-RNAs in CuAAC and SPAAC was demonstrated by RNA 5' labeling, chemical ligation including fragment joining and cyclization, and bioconjugation. As a result, several new RNA conjugates that may be valuable tools for studies on biological events such as innate immune response (cyclic dinucleotides), post-transcriptional gene regulation (circular RNAs), or mRNA turnover (m⁷G capped RNAs) were obtained.

Nucleobase Protection of Deoxyribo- and Ribonucleosides

Oligonucleotides carrying a variety of chemical modifications including conjugates are finding increasing applications in therapeutics, diagnostics, functional genomics, proteomics, and as research tools in chemical and molecular biology. The successful synthesis of oligonucleotides primarily depends on the use of appropriately protected nucleoside building blocks including the exocyclic amino groups of the nucleobases, the hydroxyl groups at the 2'-, 3'-, and 5'-positions of the sugar moieties, and the internucleotide phospho-linkage. This unit is a thoroughly revised update of the previously published version and describes the recent development of various protecting groups that facilitate reliable oligonucleotide synthesis. In addition, various protecting groups for the imide/lactam function of thymine/uracil and guanine, respectively, are described to prevent irreversible nucleobase modifications that may occur in the presence of reagents used in oligonucleotide synthesis. © 2017 by John Wiley & Sons, Inc.

Crystal structure of N′-(2-phenylacetyl)thiophene-2-carbohydrazide monohydrate, C13H14N2O3S

C13H14N2O3S, monoclinic, C2/c (no. 15), a = 27.9910(12) Å, b = 6.5721(3) Å, c = 14.2821(7) Å, β = 92.600(3)°, V = 2624.6(2) Å3, Z = 8, R gt(F) = 0.042, wR ref(F 2) = 0.105, T = 100 K.

Additions of Thiols to 7-Vinyl-7-deazaadenine Nucleosides and Nucleotides. Synthesis of Hydrophobic Derivatives of 2'-Deoxyadenosine, dATP and DNA

Additions of alkyl- or arylthiols to 7-vinyl-7-deaza-2'-deoxyadenosine gave a series of 7-[2-(alkyl- or arylsulfanyl)ethyl]-7-deaza-2'-deoxyadenosines in 45-85% yields. The nucleosides were converted to 5'-O-mono-(dA^SRMP) or triphosphates (dA^SRTP) by phosphorylation. The modified triphosphates were also prepared by thiol addition to 7-vinyl-7-deaza-dATP. The triphosphates dA^SRTP were good substrates for DNA polymerases useful in the enzymatic synthesis of base-modified oligonucleotides (ONs) or DNA containing flexibly linked hydrophobic substituents in the major groove. Primer extension was used for the synthesis of ONs with one or several modifications, PCR was used for the synthesis of heavily modified DNA, whereas terminal deoxynucleotidyl transferase was used for a single-nucleotide labeling of the 3'-end.

Aptamers: Promising Tools for the Detection of Circulating Tumor Cells

Circulating tumor cells (CTCs) are cells that shed from a primary tumor and freely circulate in the blood, retaining the ability to initiate metastasis and form a secondary tumor in distant organs in the body. CTCs reflect the molecular profile of the primary tumor, therefore studying CTCs can allow for an understanding of the mechanism of metastasis, and an opportunity to monitor the prognosis of cancer. Unfortunately, the detection of CTCs is a considerable challenge due to their low abundance in the bloodstream and the lack of consistent markers present to recognize these cells. The aim of this review is to summarize some of the aptamer-based affinity methods for the detection of CTCs. The basic biological concept of how metastasis occurs and the role of CTCs in this process are presented. Some methods of CTC detection employing antibodies or peptides are mentioned here for comparison. The review of present literature suggests that aptamers are emerging as competitive technology in the detection of CTCs, especially due to their unique properties, but there still remain several challenges to be met, including the need to improve the throughput and sensitivity of such methods.

Selective chemical modification of DNA with alkoxy- and benzyloxyamines

DNA is modified selectively at cytosine with benzyloxyamine and -derivatives carrying handles for click reactions.

Assembling multiporphyrin stacks inside the DNA double helix

Double stranded DNA hybrids containing up to four consecutive, face-to-face stacked porphyrins are described. Non-nucleosidic, 5,15-bisphenyl-substituted porphyrin building blocks were incorporated into complementary oligonucleotide strands. Upon hybridization multiple porphyrins are well accommodated inside the DNA scaffold without disturbing the overall B-DNA structure. The formation of double strands containing up to four free base porphyrins is enabled without compromising duplex stability. UV/vis, fluorescence, and CD spectroscopy demonstrate the formation of porphyrins H-aggregates inside the DNA double helix and provide evidence for the existence of strong excitonic coupling between interstrand stacked porphyrins. H-aggregation results in considerable fluorescence quenching. Most intense CD effects are observed in stacks containing four porphyrins. The findings demonstrate the value of DNA for the controlled formation of molecularly defined porphyrin aggregates.

Efficient functionalization of oligonucleotides by new achiral nonnucleosidic monomers

A novel synthetic strategy has been designed for preparation of achiral nonnucleosidic phosphoramidite monomers for automated solid-phase oligonucleotide synthesis. It is based on O-DMTr-protected 4-(2-hydroxyethyl)-morpholine-2,3-dione as the key compound and a family of building blocks obtained by its ring-opening by primary aliphatic amines. A series of nonnucleosidic phosphoramidites containing various side-chain functionalities was synthesized, and corresponding oligodeoxyribonucleotides incorporating modified units in single or multiple positions along the chain were prepared.

Alternative synthetic tools to phospho-specific antibodies for phosphoproteome analysis: progress and prospects

Signal transduction cascades in living systems are often controlled via post-translational phosphorylation and dephosphorylation of proteins. These processes are catalyzed in vivo by kinase and phosphatase enzymes, which consequently play an important role in many disease states, including cancer and immune system disorders. Current techniques for studying the phosphoproteome (isotopic labeling, chromatographic techniques, and phosphospecific antibodies), although undoubtedly very powerful, have yet to provide a generic tool for phosphoproteomic analysis despite the widespread utility such a technique would have. The use of small molecule organic catalysts that can promote selective phosphate esterification could provide a useful alternative to current state-of-the-art techniques for use in, e.g., the labeling and pull-down of phosphorylated proteins. This report reviews current techniques used for phosphoproteomic analysis and the recent use of small molecule peptide-based catalysts in phosphorylation reactions, indicating possible future applications for this type of catalyst as synthetic alternatives to phosphospecific antibodies for phosphoproteome analysis.

Solid-phase supports for oligonucleotide synthesis

This unit attempts to provide a reasonably complete inventory of over 280 solid supports available to oligonucleotide chemists for preparation of natural and 3'-modified oligonucleotides. Emphasis is placed on non-nucleosidic solid supports. The relationship between the structural features of linkers and their behavior in oligonucleotide synthesis and deprotection is discussed wherever the relevant observations are available.

Synthesis of a Candida albicans tetrasaccharide spanning the β1,2-mannan phosphodiester α-mannan junction

The cell wall phosphomannan of Candida species is a complex N-linked glycoprotein with a glycan chain containing predominantly an α-linked mannose backbone with α-mannose branches. A minor β-mannan component is attached to the branches either via a glycosidic bond (acid stable β-mannan) or a phosphodiester bond (acid-labile β-mannan). The α-mannan residues of the cell wall phosphomannan do not afford protective antibody, while the β-mannan portion is a protective antigen and has become an attractive target as the key epitope of a conjugate vaccine. We report the first synthesis of a tetrasaccharide 1 consisting of a β1,2-mannopyranosyl trisaccharide linked via a phosphodiester to methyl α-mannopyranoside. This encompasses the attachment site of the acid labile β-mannan to the α-mannan component of the cell wall phosphomannan. The trisaccharide was formed by an iterative process to first create a β-glucopyranoside linkage and then epimerize the C-2 center via an oxidation-reduction sequence. The phosphate diester linkage was accessed via an anomeric H-phosphonate. The binding of phosphomannan fragment 1 with the protective antibody C3.1 has been evaluated and compared with a β-mannotrioside in hapten inhibition experiments. The observed activities are rationalized with a model for docked in the binding site of C3.1.

Challenges and opportunities for small molecule aptamer development

Aptamers are single-stranded oligonucleotides that bind to targets with high affinity and selectivity. Their use as molecular recognition elements has emerged as a viable approach for biosensing, diagnostics, and therapeutics. Despite this potential, relatively few aptamers exist that bind to small molecules. Small molecules are important targets for investigation due to their diverse biological functions as well as their clinical and commercial uses. Novel, effective molecular recognition probes for these compounds are therefore of great interest. This paper will highlight the technical challenges of aptamer development for small molecule targets, as well as the opportunities that exist for their application in biosensing and chemical biology.

Synthesis and properties of squaraine-modified DNA

The incorporation of squaraines into DNA via the phosphoramidite approach is described. High molar absorptivity, environment-sensitive fluorescence properties and intense CD effects render squaraines valuable building blocks for DNA-based optical probes and nanostructures.

Synthesis of oligonucleotides carrying thiol groups using a simple reagent derived from threoninol

Oligonucleotides carrying thiol groups are useful intermediates for a remarkable number of applications involving nucleic acids. In this study, DNA oligonucleotides carrying tert-butylsulfanyl protected thiol groups have been prepared. A building block derived from threoninol has been developed to introduce a thiol group at any predetemined position of an oligonucleotide. The resulting thiolated oligonucleotides have been used for the preparation of oligonucleotide conjugates and for the functionalization of gold nanoparticles using the reactivity of the thiol groups.

Synthesis and application of highly reactive amino linkers for functional oligonucleotides

Oligonucleotides are functionalized by conjugation with a variety of molecules, and aliphatic amino linkers have been frequently used as a tether for their modifications. This unit describes the syntheses and applications of novel amino linkers having a carbamate structure. Two major chemical properties of the primary amine are induced by the neighboring effect of the carbamate group, which are found to be optimum in an aminoethyl carbamate structure. First, the hydrophobic monomethoxytrityl group can be rapidly removed from the aminoethyl carbamate under very mild acidic conditions, while the deprotection is not completed in standard aliphatic amines even under high acid concentration. This significant feature enables the convenient purification of amino-modified oligonucleotides by using the hydrophobic interaction of the monomethoxytrityl group with a reverse-phase resin. Second, the introduction of the carbamate linkage reduces the pK(a) value of the neighboring primary amine, resulting in an increase in the conjugation yields with various functional molecules, such as those having active esters. The novel amino linkers that have an aminoethyl carbamate linkage indicate potent activity and are applicable for the preparation of various functional oligonucleotides.

31P NMR and computational studies on stereochemistry of conversion of phosphoramidate diesters into the corresponding phosphotriesters

31P NMR spectroscopy was used to investigate a stereochemical course of a nitrite-promoted conversion of phosphoramidate diesters into the corresponding phosphotriesters. It was found that this reaction occurred with almost complete epimerization at the phosphorus center and at the C1 atom in the amine moiety. On the basis of the 31P NMR data, a plausible mechanism for the reaction was proposed. The density functional theory calculation of the key step of the reaction, i.e., breaking of the P-N bond and formation of the P-O bond, suggested a one-step S(N)2(P) process with retention of configuration at the phosphorus center.

Postsynthetic modification of oligonucleotides with imidazophenazine dye and its effect on duplex stability

Carboxyalkyl derivative of the intercalating agent imidazo[4,5-b]phenazine was used for the postsynthetic oligonucleotide modification. Model pentadecathymidylate-imidazophenazine conjugate was prepared from 5'-aminoalkyl-modified (dT)(15) by using phosphonium coupling reagent BOP in the presence of 1-hydroxybenzotriazole. Spectral-fluorescent properties of the conjugate were studied. The attachment of the dye was found to increase the thermal stability of (dT)(15) duplex with poly(dA) by more than 4°C, probably by the intercalation mechanism.

5'-Bis-conjugation of oligonucleotides by amidative oxidation and click chemistry

A pent-4-ynyl tert-butyl N,N-diisopropyl phosphoramidite was coupled at the 5'-end of oligonucleotides to give a phosphite triester linkage, which forms an H-phosphonate diester linkage during treatment with dichloroacetic acid. Then an amidative oxidation with CCl(4) in the presence of an amine and a 1,3-dipolar cycloaddition with an azide under copper(I) catalysis afforded the bis-conjugated oligonucleotides with high efficiency. The introduction of a bromoalkyl group as a precursor of azidoalkyl by amidative oxidation allowed the performance of two selective 1,3-dipolar cycloadditions.

Solid-phase synthesis of oligodeoxynucleotides containing N4-[2-(t-butyldisulfanyl)ethyl]-5-methylcytosine moieties

An efficient route for the synthesis of the phosphoramidite derivative of 5-methylcytosine bearing a tert-butylsulfanyl group protected thiol is described. This building block is used for the preparation of oligonucleotides carrying a thiol group at the nucleobase at the internal position of a DNA sequence. The resulting thiolated oligonucleotides are useful intermediates to generate oligonucleotide conjugates carrying molecules of interest at internal positions of a DNA sequence.

Orally bioavailable anti-HBV dinucleotide acyloxyalkyl prodrugs

The acyloxyalkyl derivatives of a model anti-HBV dinucleotide were synthesized and evaluated as orally bioavailable prodrugs. Our studies have led to the identification of the first orally bioavailable dinucleotide prodrugs for further therapeutic development against the hepatitis B virus (HBV).

Azide solid support for 3'-conjugation of oligonucleotides and their circularization by click chemistry

A solid support bearing an azido linker was used to synthesize a 3'-azido-alkyl-oligonucleotide by phosphoramidite chemistry. The resulting oligonucleotide was either conjugated by 1,3-dipolar cycloaddition on solid support or in solution with mannose-propargyl derivative and in solution with dansyl propargyl. Besides, after introduction of an alkyne function at the 5'-end, the resulting oligonucleotide bearing both 3'-azide and 5'-alkyne functions was circularized.

Nucleic acid-guided assembly of aromatic chromophores

The rational formation of aromatic chromophore arrays is an intriguing challenge since ordered collectives of chromophores possess properties that are largely different from those of the individual molecules. Therefore, nucleic acids are increasingly used as scaffolds for the construction of multi-chromophore arrays. This tutorial review provides an introduction to the field of nucleic acid-guided chromophore assemblies for non-specialists and a reference point for those familiar with the area by highlighting the recent developments and describing some of the spectroscopic methods used for the study of oligonucleotide-chromophore conjugates.

Polyfluorophores on a DNA backbone: a multicolor set of labels excited at one wavelength

We recently described the assembly of fluorescent deoxyriboside monomers ("fluorosides") into DNA-like phosphodiester oligomers (oligodeoxyfluorosides or ODFs) in which hydrocarbon and heterocyclic aromatic fluorophores interact both physically and electronically. Here we report the identification of a multicolor set of water-soluble ODF dyes that display emission colors across the visible spectrum, and all of which can be simultaneously excited by long-wavelength UV light at 340-380 nm. Multispectral dye candidates were chosen from a library of 4096 tetramer ODFs constructed on PEG-polystyrene beads using a simple long-pass filter to observe all visible colors at the same time. We resynthesized and characterized a set of 23 ODFs containing one to four individual chromophores and included 2-3 spacer monomers to increase aqueous solubility and minimize aggregation. Emission maxima of this set range from 376 to 633 nm, yielding apparent colors from violet to red, all of which can be visualized directly. The spectra of virtually all ODFs in this set varied considerably from the simple combination of monomer components, revealing extensive electronic interactions between the presumably stacked monomers. In addition, comparisons of anagrams in the set (isomers having the same components in a different sequence) reveal the importance of nearest-neighbor interactions in the emissive behavior. Preliminary experiments with human tumor (HeLa) cells, observing two ODFs by laser confocal microscopy, showed that they can penetrate the outer cellular membrane, yielding cytoplasmic localization. In addition, a set of four distinctly colored ODFs was incubated with live zebrafish embryos, showing tissue penetration, apparent biostability, and no apparent toxicity. The results suggest that ODF dyes may be broadly useful as labels in biological systems, allowing the simultaneous tracking of multiple species by color, and allowing visualization in moving systems where classical fluorophores fail.

Solid-supported reagents for synthesis of nucleoside monothiophosphates, dithiodiphosphates, and trithiotriphosphates

This unit describes procedures for the selective synthesis of nucleoside monothiophosphates, dithiodiphosphates, and trithiotriphosphates from solid-supported phosphitylating reagents. Rigid and sterically hindered polymer-bound 1,3,2-oxathiaphospholane is reacted selectively with the 5'-hydroxyl group of nucleosides in the presence of 1H-tetrazole. Sulfurization in the presence of Beaucage's reagent (3H-1,2-benzodithiole-3-one 1,1-dioxide) followed by ring-opening with 3-hydroxypropionitrile and basic cleavage in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) through the elimination of polymer-bound ethylene episulfide afford nucleoside monothiophosphates. Furthermore, reaction of polymer-bound diphosphitylating and triphosphitylating reagents, prepared from polymer-bound benzyl alcohol, with unprotected nucleosides, sulfurization with Beaucage's reagent, and acidic cleavage using trifluoroacetic acid cocktail produce nucleoside dithiodiphosphates and trithiotriphosphates in moderate yields.