MonoPhos

Cytidine-5 -monophos-phate, glucose-1-phosphate Prostate phosphate monoesterase is employed to hydrolyze to cytidine, glucose and orthophosphate [42]... 

Write a structural formula for 2 -deoxycytidine 3 -monophos- phate. You may wish to refer to Table 28.2 for the structure of cytidine. J... 

Several TLR-4 adjuvants for vaccines have been developed to date. An example of these is monopho-sphoryl lipid A (MJPL) a modified version of lipid A found in LPS [4]. It has been used extensively in clinical trials as it is far less toxic than LPS. It is hoped to use MPL in vaccines against infectious diseases, allergies and cancer. Derivatives of MPL have now been... 

HN=CR 2, the presence of triethylamine. When at least one of the groups is alkoxy, these phosphines may be converted into monophos-phazenes by a quaternization and subsequent pyrolysis ... 

The tveak and reversible binding of these complexes to calf-thymus DNA (ct DNA) suggests a dominant electrostatic mode of interaction nevertheless, relevant conformational distortions of the double helix are caused [50]. A multinuclear NMR study of the reactivity of [Au(en)Cl2]Cl and [Au(en)2]Cl3 vith guanosine 5 -monopho-sphate (5 -GMP) reveals that in an aqueous solution only [Au(en)Cl2]Cl binds very weakly to 5 -GMP via N(7) to give a 1 1 adduct [48]. 

An example of a 103Rh-31P correlation experiment of Rh(MonoPhos)2-(COD)BF4 is shown in Figure 11.5. Here also, two inequivalent 31P atoms are connected to the same Rh center [23]. 

The use of monodentate phosphoramidites in enantioselective hydrogenation was first reported in 2000, together with reports on the use of phosphites and phospho-nites [15]. Phosphoramidites are prepared in a variety of ways, but the most common route is the treatment of a diol with PC13, followed by addition of an amine [60, 61]. MonoPhos (29a), the first reported phosphoramidite used as a ligand, is prepared from BINOL and HMPT in toluene [62]. Phosphoramidites, especially... 

The immobilization of catalysts on a solid support is a well-known approach to render a system recycleable, and this has been performed recently by the immobilization of rhodium-MonoPhos 29 a on aluminosilicate A1TUD-1. The resultant system showed high efficiency in water, and could be recycled [80]. 

Another way of retaining the catalyst is to create dendrimer-supported ligands, thereby allowing separation of the product and catalyst by membranes. Based on the readily modified BICOL backbone, two dendrimer-Hgands 43 were prepared that had performance comparable to that of MonoPhos 29 a in the hydrogenation of methyl N-acyl dehydrophenylalanine [81]. 

It transpires that most classes of monodentate ligands include members that are able to induce high enantioselectivity in the hydrogenation of the two benchmark substrates 52 a and 53 a. It is not clear whether their corresponding acids 52b and 53 b have been studied or, alternatively, if the authors decided not to include (disappointing) ee-values. For phosphoramidite MonoPhos (29 a), however, the ee-values are invariably excellent. Overall, the TOFs range from 50 to 170 IT1, but have not been optimized in most cases. Unfortunately, with one exception [87], the hydrogenation of dehydroamino esters in which R1 is a (functionalized) alkyl substituent has not been studied, probably because of their difficult accessibility. 

For an initial study using the phosphora-midite MonoPhos, see M. van den Berg, A.J. Minnaard, R.M. Haak, M. Leeman, E.P. Schudde, A. Meetsma, B.L. Feringa,... 

MonoPhos 29a has shown to give the same ee-values for N-acyl, N-BOC and N-Z protection (unpublished results). 

The use of 2 equiv. of MonoPhos (10 a) in the rhodium-catalyzed enantioselective hydrogenation of the key cinnamic acid derivative 15 resulted in the formation of 16 in 50% conversion and 20% ee after 5 h in isopropanol at 60 °C and 25 bar of hydrogen. Other phosphoramidites, such as the sterically demanding ligand 10 c, resulted in slightly better activity and enantioselectivity. In seeking a... 

Few data are available for rhodium complexes based on monodentate ligands. In a recent study, the rate of COD hydrogenation in Rh(MonoPhos)2(COD)BF4 was determined as 0.071 min-1, which is somewhat slower than the corresponding DuPhos complex [20]. 

Nitrile groups in the substrate may also cause problems. Minnaard, Feringa and de Vries reported the enantioselective hydrogenation of a range of substituted 2-acetamido-cinnamates at 5 bar pressure using Rh/MonoPhos. Whereas most substrates could be hydrogenated with turnover frequencies (TOFs) of between 200 IT1 and 600 h-1, the 4-cyano-substituted substrate was hydrogenated very slowly at this pressure with a TOF of only 4 h 1 [40]. 

Acetonitrile is another solvent that may retard the reaction. Although no cases of inhibition by acetonitrile have been described in the literature, we usually find no hydrogenation activity at all when using rhodium/MonoPhos catalysts in this solvent Presumably, this is true for most transition metal catalysts. 

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