BMEG Oligonucleotides For Efficient Cellular Delivery - ChemGenes now offers BMEG Masked phosphoramidites and Oligonucleotides For Targeted Cellular Delivery of Oligonucleotides.1,2
- There is great demand in fields of gene therapy and molecular biology for methods or compounds that effectively deliver bio-molecules such as proteins, nucleic acids and other biologically active molecules into cells, tissues and organs.
- In order for an oligonucleotide to be useful in therapeutics, an effective amount of active bio-molecule must be delivered into the target cells or tissue. At the same time, nucleic acid delivery methods should minimize immune responses or cytotoxicity to the host.
- Current methods for delivery of negatively charged bio-molecules include viral and non-viral based delivery systems. Even though these methods have several advantages, they suffer from drawbacks such as narrow range of cell infectivity and cytotoxic to the cell. Accordingly, there exists a need for improved biomolecule delivery systems.
- ChemGenes now offers novel BMEG (S-isobutanoyl 2-(2-mercaptoethoxy)ethoxyl) phosphoramidite monomers (Figure 1). BMEG serves as irreversible masking group for efficient cellular delivery.

Figure 1: Structure of the various BMEG deoxy and ribo phosphoramidites.
Advantages of BMEG group:
- BMEG thioesters are thermally stable due to highly unfavored 8 membered transition state.
- Sterically bulk isopropyl group of the thioester chemically stabilizes the center to bas.
- Lipophilicity of the BMEG group helps in improved cellular delivery across cell membranes in vitro and in vivo.
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BMEG group reversibly masks negative charge(s) of an oligonucleotide. As a result, oligonucleotides containing these modifications have less negative total charge when compared to RNA or DNA of the same sequence.
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Since the overall reduced negative charge in these bio-polymers, they are called “Ribo-Nucleic Neutral (RNN)” and “Deoxyribo-Nucleic-Neutral (DNN)”.
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BMEG phosphate protecting groups do not interfere with duplex formation.
Oligonucleotide synthesis:
- BMEG phosphoramidite monomers are protected with ultra-mild deprotection groups such as Phenoxyacetyl (PAC), isopropylphenoxyacetyl (iPrPAC); Acetyl (Ac) and Dimethylformamidine (DMF). It is recommended to use mild deprotecting supports such as Q-supports or oxalyl supports.
- The full length siRNN constructs of 21 nucleosides with at least 5 siRNN nucleotide insertions are successfully synthesized, isolated and cleanly purified.
- BMEG masked oligonucleotides are engineered to be bio-labile, such that the BMEG group(s) are cleaved from the biomolecule upon intracellular delivery and results in the Bio-compatible byproducts (Figure 2).

Applications of BMEG oligonucleotides in siRNA technology:
- Figure 3 shows results form knockdown of Green Fluorescence Protein (GFP) expression using siRNN that contain five BMEG monomers (BMEG 5N g2Mod/p2Mod15 nM). U2F 5N g2 Mod is a positive control SiRNA that demonstrates the maximum achievable level of reduction of dGFP expression by a construct that does not have phosphotriester protecting groups.
- The results of this experiment indicated that siRNN oligos that contain five BMEG monomers were able to load into the RISC complex and elicit a reduction in protein expression intracellularly up to 94%.

Figure 3: Green Fluorescence Protein (GFP) knockdown as response over time is shown for selected siRNN at 48 h, 72 h and 96 h.
References:
1. Petersen, S. G. Patent number WO 2010039543 A2 “Self delivering bio-labile phosphate protected pro-oligos for oligonucleotide based therapeutics and mediating RNA interference”.
2. World wide exclusive license to ChemGenes Corporation, USA.