Ligand pairs

Sharpless Asymmetric Dihydroxylation (AD) - Ligand pair are really diastereomers ... 

The development of effector T cells following activation by antigen-presenting cells also requires the interaction of another receptor-ligand pair. CD40 molecules on antigen-presenting cells are required to bind... 

The direct interaction depends on the distance between the ligands and has the same range as the ligand-ligand pair potential. The indirect correlation, in this particular model, is independent of the ligand-ligand distance. It does depend on... 

SOLVENT EFFECT ON THE LIGAND-LIGAND PAIR CORRELATION... 

The first model is that discussed in Section 4.3. This may be called the one-macrostate approximation. In this model the adsorbent molecule has only one state, and the binding process does not induce any conformational changes. Hence, the ligand-ligand pair correlation is due only to the direct ligand-ligand interaction... 

The model is that discussed in Section 4.5, for which the ligand-ligand pair correlation has the form... 

We shall now examine the effect of size on the cooperativity. We use the model of Section 4.5, for which we found the formal expression for the ligand-ligand pair correlation 1, 1) in Eq. (9.3.16). The solvent effect enters this expression via three factors, which we shall examine separately. 

The second case is when the reservoir is a solution of the ligand in a solvent, say water. The form of the BI is the same, except for areinterpretation of the quantity G . In Eq. (D.7), G is an integral over the pair correlation function of the ligands in vacuum, i.e., in Eq. (D.9) is the ligand-ligand pair potential. In the case... 

The complexes [lr(COD)(NCMe)(PR3)]BF4 (PR3 = P Pr3, PMe3), which are closely related to Crabtree s catalyst, also contain mixed ligands, very basic phosphines, P Pr3 or PMe3, and a nitrogen donor ligand, acetonitrile. These mixed-ligand pair combinations have been shown to be very useful for spectroscopic observations and have provided detailed information on the mechanism of reactions performed by those complexes [9, 10]. 

Both the selectivity and the activity of the diastereomeric ligands, (Rp,S)-5a and (Sp,S)-5a, were nearly identical and both showed positive chiral cooperativity (there was no observation of a mismatched pair). Through introduction of a phenyl residue in the a-position of the side-chain as shown in ligand pair 6a, there was again a small matched/mismatched effect, which was not as strong as in the unsubstituted case in ligand pair 4a. Overall, we could derive a simple rule for the ligands ... 

The first example synthesized was based on the AHPC structure with (S)-cy-clohexylethylamine in the side-chain. The use of the more sterically hindered (S)-cyclohexylethylamine in the side-chain increased the enantiomeric excess from 83% ee (with (Sp,S)-5a to 90% ee with (Sp,S)-5b (complete conversion). The other diastereomer, (Pp,S)-5b, resulted in 94% yield and 87% ee. The ligand pair 6b, which is based on BHPC with (S)-t-butylethylamine in the side-chain, resulted in a matched/mismatched pair. The (Rp,S) diastereomer gave a 98% yield and an excellent 89% ee, but the (Sp,S) diastereomer produced only a 25% yield with a moderate 42% ee. The diastereomeric pair 6c, also based on BHPC 3 with (S)-naphthalen-l-ylethylamine in the side-chain, resulted similarly in a matched/mismatched pair with high activity, but only moderate enantiomeric excess. 

There are two reasonable structural results of C02 insertion since the metal-ligand pair may add across the carbon-oxygen double bond in two different ways yielding (29) or (30), depending in part on the polarity of the M—X bond. 

Spada, S. and Pliickthun, A. (1997) Selectivity infective phage (SIP) technology A novel method for in vivo selection of interacting protein-ligand pairs. Nat. Med. 3, 694—696. 

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