Pentyl groups

The relative stereochemistry of hyperaspine (1) was determined by 2D NMR and MS methods. It has a m-fused bicyclic conformation 82 (01TL4621). The tram-fused one is disfavored by an axial pentyl group at C(8) and by a destabilising dipole-dipole interaction between the N and O atoms, which does not exist in the alternative cis conformation. 

In the course of investigations on the synthesis of ( + )-biotin (7) the addition of isothiocyana-toacetate enolates 8 to 1,3-thiazolines 9 has been studied16 17. The diastereofacial selectivity of these reactions is controlled by attack of the enolate on the imine face opposite the 5-pentyl group and correctly establishes the relative stereochemistry at C-l and C-2 of biotin. 

The relative stereochemistry of hyperaspine 93 was determined by 2-D NMR spectroscopic and mass spectrometry (MS) methods. It has a m-fused bicyclic conformation 93a <2001TL4621>. The trans-fused one is disfavored by an axial pentyl group at C-8 and by a destabilizing dipole-dipole interaction between the N- and O-atoms, which does not exist in the alternative //.(-conformation. The geminal coupling constant of C( 1 )H2 in 93 (11.0 Hz), and that of its 6-hydroxy derivative (11.2 Hz), indicates that they exist preferentially in / //-conformations, whereas their 6-epimers adopt trans-conformations (9.3 and 8.4 Hz, respectively) <2005EJ01378>. Nuclear Overhauser enhancement spectroscopy (NOESY) studies also confirmed the stereochemistry of 93 by the marked nuclear Overhauser effect (NOE) correlation between H-3 and H-4a <20030L5063>. 

Alkenyl nitrones, having the alkene connected to the nitrone nitrogen atom, have been used in another approach to intramolecular reactions (231-235). Holmes and co-workers have this method for the synthesis of the alkaloid (—)-indolizidine 209B 137 (210,231). The alkenyl nitrone 134, was obtained from the chiral hydroxylamine 133 and an aldehyde. In the intramolecular 1,3-dipolar cycloaddition, 135 was formed as the only isomer (Scheme 12.45). The diastereofacial selectivity was controlled by the favored conformation of the cyclohexane-like transition state in which the pentyl group was in a pseudoequatorial position, as indicated by 134. Further transformation of 135 led to the desired product 137. 

The usual selectivities are observed, with aryl alkyl ketones and alkyl methyl ketones being reduced with high enantioselectivity (1 -> 2 and 3 -> 4)). That 5 is reduced to 6 with high , with the reducing enzymes differentiating between an ethyl and an -pentyl group, is even more impressive. 

Fig. 6. Definition of STERIMOL parameters as for the 2-pentyl group having fully extended staggered conformation...

SAMPLE SOLUTION (a) An examination of the structural formula of 1-heptyne reveals it to have a pentyl group attached to an acetylene unit. Alkylation of acetylene, by way of its anion, with a pentyl halide is a suitable synthetic route to 1-heptyne. 

Figure 8.13 The two Shell-types of antiagglomerant. On the left is the water-soluble type, with one branch (Rj) containing 8-18 carbons. On the right is the oil-soluble type with two branches (Rj) with 8-18 carbons. The central atom is nitrogen or phosphorus, and the shorter branches (R2) are butyl- or pentyl-groups.

QAS Quaternary center with butyl or pentyl groups Nalco (Cowie et al., 2003)... 

Pick the longest continuous chain that includes both carboxyl groups and name the compound as a -dioic acid. This chain contains only three carbons and bears a pentyl group as a substituent at C-2. It is not necessary to specify the position of the pentyl group, because it can only be attached to C-2. 

M-Pentane -Pentyl group Asterisk denotes point attachment to molecule ... 

In contrast, in the orthorhombic needles, there is only one molecule in the asymmetric unit and it has a different external shape. While the nine-membered ring at the core of this molecule is planar, one of the pentyl groups protrudes nearly vertically, as seen in Parts B and C of Fig. 10. The molecular packing involves a stair step arrangement of trimers with relatively long distances between them with the closest contact of 3.618(2) A. The absence of strong aurophilic interactions between trimers may be responsible for the non-emissive nature of this polymorph. 

An X-ray crystal structure of peramivir (24) in complex with influenza A N9 showed interactions of the 3-pentyl group with S4 and S5 [117]. Due to the different stereochemistry of the guanidino moiety of 24 compared to zanamivir, a water molecule was displaced from S2 when 24 was bound. The different binding mode of the guanidine moiety within the active site provided the reason by which 24 showed inhibitory activity also for zanamivir-resistant influenza virus sialidase strains [117,120], Compound 24, which showed comparable or better efficacy in vivo than zanamivir and oseltamivir [121, 122], successfully completed animal studies and is in phase III clinical trials. 

In the previous example the elimination could occur only in the pentyl group because the other three substituents on the nitrogen are methyl groups, which do not have /3-carbons. However, if more than one of the alkyl groups bonded to the nitrogen is larger than methyl, then elimination can, in principle, involve any of these groups. 

Start by analyzing whether the bromo. nitro, or pentyl groups can be added to the appropriate disubstituted benzene with the required orientation. 

The NOj group can be attached ortho to the pentyl group and para to the Br. 

The pentyl group must be put on by a Friedel-Crafts acylation reaction followed by a reduction to avoid rearrangement. The bromine must be added at the acyl stage to get meta orientation. 

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