Cut-and-Paste DNA Insertion with Engineered Type V-K CRISPR-associated Transposases

CRISPR-associated transposases (CASTs) enable recombination-independent, multi-kilobase DNA insertions at RNA-programmed genomic locations. Type V-K CASTs offer distinct technological advantages over type I CASTs given their smaller coding size, fewer components, and unidirectional insertions. However, the utility of type V-K CASTs is hindered by a replicative transposition mechanism that results in a mixture of desired simple cargo insertions and undesired plasmid co-integrate products. Here, we overcome this limitation by engineering new CASTs with dramatically improved product purity. To do so, we compensate for the absence of the TnsA subunit in multiple type V-K CASTs by engineering a Homing Endonuclease-assisted Large-sequence Integrating CAST compleX, or HELIX system. HELIX utilizes a nicking homing endonuclease (nHE) fused to TnsB to restore the 5-prime nicking capability needed for dual-nicking of the DNA donor. By leveraging distinct features of both type V-K and type I systems, HELIX enables cut-and-paste DNA insertion with up to 99.3% simple insertion product purity, while retaining robust integration efficiencies on genomic targets. Furthermore, we demonstrate the versatility of this approach by generating HELIX systems for other CAST orthologs. We also establish the feasibility of creating a minimal, 3-component HELIX, simplifying the number of proteins that must be expressed. Together, HELIX streamlines and improves the application of CRISPR-based transposition technologies, eliminating barriers for efficient and specific RNA-guided DNA insertions.

Synthesis and Evaluation of C2-Symmetric SPIROL-Based bis-Oxazoline Ligands

This communication describes the synthesis of new bis-oxazoline chiral ligands (SPIROX) derived from the C2-symmetric spirocyclic scaffold (SPIROL). The readily available (R,R,R)-SPIROL (2) previously developed by our group was subjected to a three-step sequence that provided key diacid intermediate (R,R,R)-7 in 75% yield. This intermediate was subsequently coupled with (R)- and (S)-phenylglycinols to provide diastereomeric products, the cyclization of which led to two diastereomeric SPIROX ligands (R,R,R,R,R)-3a and (R,R,R,S,S)-3b in 85% and 79% yield, respectively. The complexation of (R,R,R,R,R)-3a and (R,R,R,S,S)-3b with CuCl and Cu(OTf)2 resulted in active catalysts that promoted the asymmetric reaction of α-diazopropionate and phenol. The resultant O–H insertion product was formed in 88% yield, and with excellent selectivity (97% ee) when ligand (R,R,R,R,R)-3a was used.

CO2 activation by ligand-free manganese hydrides in a parahydrogen matrix

The reaction of MnH2 with CO2 gave insertion product HMn(η2-O2CH) by concerted hydride ion transfer.

1,2- and 1,1-Migratory Insertion Reactions of Silylated Germylene Adducts

The reactions of the PMe3 adduct of the silylated germylene [(Me3Si)3Si]2Ge: with GeCl2·dioxane were found to yield 1,1-migratory insertion products of GeCl2 into one or two Ge–Si bonds. In a related reaction, a germylene was inserted with tris(trimethylsilyl)silyl and vinyl substituents into a Ge–Cl bond of GeCl2. This was followed by intramolecular trimethylsilyl chloride elimination to another cyclic germylene PMe3 adduct. The reaction of the GeCl2 mono-insertion product (Me3Si)3SiGe:GeCl2Si(SiMe3)3 with Me3SiC≡CH gave a mixture of alkyne mono- and diinsertion products. While the reaction of a divinylgermylene with GeCl2·dioxane only results in the exchange of the dioxane of GeCl2 against the divinylgermylene as base, the reaction of [(Me3Si)3Si]2Ge: with one GeCl2·dioxane and three phenylacetylenes gives a trivinylated germane with a chlorogermylene attached to one of the vinyl units.

Highly enantioselective carbene insertion into N–H bonds of aliphatic amines

Aliphatic amines strongly coordinate, and therefore easily inhibit, the activity of transition-metal catalysts, posing a marked challenge to nitrogen-hydrogen (N–H) insertion reactions. Here, we report highly enantioselective carbene insertion into N–H bonds of aliphatic amines using two catalysts in tandem: an achiral copper complex and chiral amino-thiourea. Coordination by a homoscorpionate ligand protects the copper center that activates the carbene precursor. The chiral amino-thiourea catalyst then promotes enantioselective proton transfer to generate the stereocenter of the insertion product. This reaction couples a wide variety of diazo esters and amines to produce chiral α-alkyl α–amino acid derivatives.

Selective Functionalization of Aliphatic Amines via Myoglobin-Catalyzed Carbene N–H Insertion

Engineered myoglobins have recently gained attention for their ability to catalyze a variety of abiological carbene transfer reactions including the functionalization of amines via carbene insertion into N–H bonds. However, the scope of myoglobin and other hemoprotein-based biocatalysts in the context of this transformation has been largely limited to aniline derivatives as the amine substrates and ethyl diazoacetate as the carbene donor reagent. In this report, we describe the development of an engineered myoglobin-based catalyst that is useful for promoting carbene N–H insertion reactions across a broad range of substituted benzylamines and α-diazo acetates with high efficiency (82–99% conversion), elevated catalytic turnovers (up to 7,000), and excellent chemoselectivity for the desired single insertion product (up to 99%). The scope of this transformation could be extended to cyclic aliphatic amines. These studies expand the biocatalytic toolbox available for the selective formation of C–N bonds, which are ubiquitous in many natural and synthetic bioactive compounds.

C–H Functionalization: The Shaw Synthesis of E-δ-Viniferin

Thomas Lectka of Johns Hopkins University reported (J. Org. Chem. 2014, 79, 8895) a simple protocol for free radical monofluorination, exemplified by the conversion of 1 to 2. Michael K. Hilinski of the University of Virginia used (Org. Lett. 2014, 16, 6504) a catalytic amount of the ketone 4 to mediate the oxidation of 3 to 5. Oxidation of 3 with DMDO gave the regioisomeric tertiary alcohol (not illustrated). Jeung Gon Kim and Sukbok Chang of KAIST used (Chem. Commun. 2014, 50, 12073) an Ir catalyst to convert 6 selectively to the primary sulfonamide 7. Paul J. Chirik of Princeton University employed (J. Am. Chem. Soc. 2014, 136, 12108) a Co catalyst to effect the migration of the internal alkene of 8 to the terminal alkene, that then underwent dehydrogenative silylation with 9 to deliver the allyl silane 10. Jiang Cheng of Changzhou University developed (J. Org. Chem. 2014, 79, 9847) conditions for the aminoalkylation of cyclohexane 11 with 12 to give 13. Ilhyong Ryu of Osaka Prefecture University and Maurizio Fagnoni of the University of Pavia observed (Chem. Sci. 2014, 5, 2893) high selectivity in the addition of 14 to 15. Of the five possible regioisomers, 16 dominated. In another light-mediated transformation, Shin Kamijo of Yamaguchi University and Masayuki Inoue of the University of Tokyo added (Chem. Sci. 2014, 5, 4339) 17 to 18 to give 19. Huw M. L. Davies of Emory University established (J. Am. Chem. Soc. 2014, 136, 17718) conditions for the enantioselective alkylation of a methyl ether 21 with 20 to give the ester 22. Selective methyl insertion was observed even with much more complex substrates. The trichloroethyl ester was critical for this transformation. James A. Bull of Imperial College London effected (Org. Lett. 2014, 16, 4956) selec­tive cis-arylation of the proline-derived amide 23 with 24 to give 25. E. Peter Kündig of the University of Geneva coupled (Chem. Eur. J. 2014, 20, 15021) the amine 27 with 26, then cyclized that product to the indoline 28. The enantiomeric Pd cata­lyst delivered the regioisomeric C–H insertion product.