Ligation intramolecular

Amides and sulfonamides undergo intramolecular chemistry to form aryl amides and aryl sulfonamides (Equations (17)—(19)) in the presence of palladium catalysts ligated by arylphos-phines.35,89 Initially, complexes of P(furyl)3 and P(o-tol)3 were most effective catalysts, but complexes of Hayashi s MOP and van Leeuwen s DPEphos and xantphos have lately been shown to be more active.90 In the presence of catalysts containing one of these ligand systems, five-, six-, and seven-membered rings were formed from halogenated benzamides or from substrates containing an acetamide, an A-carbobenzyloxy, or a t-butylcarbamate substituent tethered to the aryl halide (Equations (18) and (19)) ... 

DM Coltart. Peptide segment coupling by prior ligation and proximity-induced intramolecular acyl transfer. Tetrahedron 56, 3449-3491, 2000. 

The ionization is the rds. The spontaneous rate is considered to be accelerated by both inter-molecular (from the buffer) and intramolecular (from His-64) proton transfer. Cadmium can replace the native zinc from metalloenzymes and Cd nmr is being used increasingly to probe metal ligation sites in metalloproteins. The cadmium product often does not show enzyme activity however. 

Intramolecular carbon-hydrogen insertion reactions have well known to be elTectively promoted by dirhodium(ll) catalysts [19-23]. Insertion into the y-position to form five-membered ring compounds is virtually exclusive, and in competitive experiments the expected reactivity for electrophilic carbene insertion (3°>2° 1°) is observed [49], as is heteroatom activation [50]. A recent theoretical treatment [51] confirmed the mechanistic proposal (Scheme 15.4) that C-C and C-H bond formation with the carbene carbon proceeds in a concerted fashion as the ligated metal dissociates [52]. Chemoselectivity is dependent on the catalyst ligands [53]. 

The complex with two La11146 showed double metal ion cooperativ-ity (i) facile formation of metal ligated hydroxide (pKa = 7.2 at 30°C) as an intramolecular nucleophile, (ii) stabilization of the transition... 

Other very important applications of C-terminal thioester-functionalized peptides include their usage in the condensation of large unprotected peptide fragments (ligation see Vol. E22a, Section 4.1.5). 4,5,74 In this process the thioester-modified unprotected peptide reacts with the N-terminal cysteine of a second unprotected peptide giving a thioester intermediate. This step is followed by a rapid intramolecular S—>N shift with formation of the thermodynamically favored amide bond at the ligation site. 

In this method, the cyclic peptide is generated through cysteine-perthioester cyclization to afford a Xaa-Cys bond whose thiol is then used for the second ligation step to the core through a thiol addition reaction (Scheme 25).[S71 For the perthioester cyclization, the linear precursor 91 consists of an activated N-terminal Cys(Npys) and a C-terminal thiocarboxylic acid which favors cyclization due to intramolecular mixed disulfide formation between them. 

Before blunt-end ligation of an insert, the vector needs to be dephosphorylated because resealing of the two ends of the linear vector to form a circular plasmid representing an intramolecular reaction is entropically favored, and thus faster (Chapter 2, Section 2.2.3), than the intermolecular insertion of the blunt-end frag-... 

Lowe, M. P., Parker, D., Reany, O., Aime, S., Botta, M., Castellano, G., Gianolio, E., Pagliarin, R. pH-dependent modulation of relaxivity and luminescence in macrocyclic gadolinium and europium complexes based on reversible intramolecular sulfonamide ligation, J. Am. Chem. Soc. 123 (2001), 7601... 

The structure of material 6 is a 2D coordination network of twofold interpenetration, in which cubane-like Cu4I4 clusters act as connecting nodes and the dps ligands as the spacer. The intramolecular Cu—Cu distances range from 2.563(1) to 2.734(2) A. Like in the case of [ Cu(p,-I)2Cu (dps)2]ra 5, ligation... 

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