Cyclopentyl groups

EA 3167 (Fig. 43) and BZ (Fig. 44) are almost identical in structure, the former having a cyclopentyl group on the alpha carbon of the glycolic acid nucleus, while the latter has a benzyl group This minor difference seems to result in more tenacious occupancy of the muscarinic acetylcholine receptor. 

Fig. 9.10 Proposed mechanism for the synthesis of cyclopentyl silsesqui-oxane a7h3. The silsesquioxane structures are represented schematically. Each circle symbolises a siloxane unit [(c-C5H9)SiC>3] silicon atoms are represented by the circles and the oxygen atoms by the lines non-bridging lines represent -OH groups cyclopentyl groups not shown.

Restricted rotation has been observed in 151, indicating two possible orientations of the hydrophobic cyclopentyl group relative to the plane of the heterocyclic ring of adenosine receptor ligands (91TL3583). Compound 268... 

Why is the cyclopentyl group chosen for the alkoxide and the ethyl group chosen for the halide Why not use cyclopentyl bromide and sodium ethoxide to make cyclopentyl ethyl ether ... 

Straight-chain alkyl carboxylic acids derived from petroleum that also have a terminal cyclohexyl or cyclopentyl group are known as naphthenic acids. They form complexes, presumably polymeric, with many transition metals, and these compounds are freely soluble in petroleum. Copper naphthenates are used as fungicides, aluminum naphthenate was used as a gelling agent in napalm, and cobalt naphthenates are used in paints. 

Indirect substitution by a cyclopentyl group in 80% yield may be accomplished by hydrogenation of the unsaturated ester formed by condensation of cyclopentanone and cyanoacetic ester (Knoevenagel reaction) (method 37). Alkaline hydrolysis followed by thermal decarboxylation gives cyclopentylacetic acid (82%). ... 

Figure 29. Side and top views of ca. one turn of the 12-helix extracted from the crystal structure of Gellman s trans-ACPC hexamer.241 A single S(12) H bond circuit in the peptide backbone has been rendered as thick cylinders. Additionally, a residue has been rendered as a space filling model to provide a frame of reference between the two views and to more clearly show the spatial relationship between cyclopentyl groups.

Let us concentrate first of all on the situation where activity rises. Following this branch, a cyclopentyl group is now used. A cyclic structure is used since it has a larger tt value, but keeps any increase in steric factor to a minimum. If activity rises again, more hydrophobic substituents are tried. If activity does not rise, then there could be two explanations. Either the optimum hydrophobicity has been passed or there is an electronic effect (ctj) at work. Further substituents are then used to determine which is the correct explanation. 

The values reported in Table 20.7, ° allow the comparison of some characteristic alkyl groups in aromatic substitution. One will note the comparable bulkiness (Es) of the isopropyl and cyclopentyl groups, while the tertiobutyl group is far more voluminous. Furthermore, it is remarkable to observe that the electron-donor effect of the cyclopentyl group is superior to that of the cyclohexyl group. 

The cyclopentyl group creates the maximal inductive effect for a relatively reasonable bulkiness. It is often a good filling of a hydrophobic pocket as illustrated for the cAMP phosphodiesterase inhibitor rolipram (Figure 20.15). The inhibitory activity toward type IV cAMP-phosphodieste-rase is increased 10 times when the meto-methoxy group is replaced by a mem-cyclopentyl group (rofipram)." ... 

Presumably the cyclopentyl rest fills, in an optimal manner, a hydrophobic pocket of the active site of the enzyme. The cyclopentyl group has also proven advantageous in replacing a em-dimethyl in a series of inhibitors of acyl-CoA-cholesterol acyltransferase, which is an enzyme implied in the absorption of the alimentary cholesterol." ... 

The cocrystal structure of 57 with ERa revealed that the more favorable interaction of the 5-OH with His524 compensates for the shift in the position of the D-ring required for binding with SERBA-1. Changing the ring size of the 3,4-cyclopentyl group to a cyclohexyl or cycloheptyl did not have much impact on either ER 3 affinity or selectivity. Attachment of a cyclopentanone (58) or cyclohexanone ring to the 3,4-position increased ERP selectivity to 100- and 40-fold, respectively, but also... 

Takaya has used a phosphine—phosphite bidentate ligand (116) to produce a copolymer with the highest reported specific optical rotation in HFIP ([ajo = -f57.2°). Nozaki has reported the effect of modifying the ligand of 116. Replacement of the phenyl groups with 3,5-dimethylphenyl (117) substituents does not effect the enantioselectivity of the polymerization. However addition of cyclopentyl groups... 

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