Phenylpropane structures

Both products could be considered to originate from dimeric phenylpropane systems by losing one of the propane side chains in addition, the stilbene (XXV) then had lost the terminal carbon of the remaining propane side chain. One therefore had to look for an appropriate dimeric phenylpropane structure which could explain the formation of these products on acidolysis. 

It is widely accepted that lignin is not a constitutionally defined compound, but that it is a physically and chemically heterogeneous material consisting of representative phenylpropane structures shown in Scheme 1. The phenylpropane units conjugate variously in the biosynthesis process and form a three dimensional polymer which does not have an ordered and regular macromolecular structure. The structural models of lignins have been illustrated by many authors, for example [12-14]. 

Figure 21 shows relationships between Tg, n and LS content of LSPU foams. It is clearly seen that the 7g value is affected by the chain length of oxyethylene chain. The amount of LS scarcely affects Tg values, especially when n value is small. In the case of LSPPU, Tg increases from 80 to 90°C with increasing LS content, since the rigid phenylpropane structure in LS acts as a hard segment efficiently in PU networks containing long oxyethylene chains of PEG. 

The -SO3H (or Na) may be attached to the ring or the side chain of the phenylpropane structure of -> lignin but is still part of a polymeric network. Commercial 1., gained from sulfite pulping (- paper), may be either spent liquor or purified 1. or their derivatives. They are soluble in water over the total pH range but not in organic solvents. 

This group of compounds is based upon the C Cj phenylpropane structure... 

Give the structure of the expected organic product in the reaction of 3 phenylpropanal with each of the following... 

The addition of methylmagnesium iodide to 2-phenylpropanal is stereoselective in producing twice as much syn-3-phenyl-2-butanol as the anti isomer (entry 5). The stereoselective formation of a particular configuration at a new stereogenic center in a reaction of a chiral reactant is called asymmetric induction. This particular case is one in which the stereochemistry can be predicted on the basis of an empirical correlation called Cram s rule. The structural and mechanistic basis of Cramls rule will be discussed in Chapter 3. 

The basic structures of flavanones, flavones, and isoflavones together with coumestrol, an intermediate in the phenylpropane metabolism, are given in Fig. 2. The 3,5,7,3 -tetrahydroxy-4 -methoxyflavanone is a nod gene inducer in Rhizo-bium leguminosarum bv. viciae the 3, 4, 5,7-tetrahydroxyflavone, in Rhizobium ineliloti and 4,7-dihydroxyisoflavone, in Bradyrhizobium japonicum. Coumestrol, an intermediate in phenylpropane metabolism, is only a weak inducer (7). 

Figure 2 Structures of flavonoids present in root exudates of host plants and inducing nod gene expression in rhizobia (1) as 3,5,7,3 -tetrahydroxy-4 -methoxyflavanone, inducer in Rhizohium legiiminosarum bv. viciae (2) as 3, 4, 5, 7-tetrahydroxy-flavone, inducer in Rhizohium melilotr, (3) as 4, 7-dihydroxyisoflavone, inducer in Bradyrhizohium japonicum (4) as couinestrol, intermediate in phenylpropane metabolism, weak inducer. (From Ref. 64.)...

Evidence for this consideration lies in the fact that the basic structure of methyl-p-methoxycinnamate is analogous to that of a p-hydroxy-phenylpropane unit from which p-hydroxybenzaldehyde could arise upon oxidation. This consideration supports and amplifies the experimental findings embodied in the phase sequence devised previously (79). 

Starting with two chiral centres, there should, therefore, be four stereoisomers, and this is nicely exemplified by the natural alkaloid (-)-ephedrine, which is employed as a bronchodilator drug and decongestant. Ephedrine is (li ,25)-2-methylamino-l-phenylpropan-l-ol, so has the structure and stereochemistry shown. 

The structural elements can be assembled in only one way and this identifies the compound as 1-bromo-3 -phenylpropane. 

Tranylcypromine ( rans-2-phenylcyclopropylamine, TCP, 8a) has close structural similarity to amphetamine (2-amino-1-phenylpropane) and is known as a nonhydrazine, nonselective, and irreversible inhibitor of both MAO A and B. It is also a potent reversible inhibitor of CAOs [36,37], Tranylcypromine has an important clinical use for treatment of certain depressive illnesses, particularly of nonendo-genous and atypical depressions and depressions associated with anxiety, agitation, phobias, and anergia [38-40], In combination with lithium, it is also applied for treatment of refractory depression [41], Recent reports also discussed MAO inhibitors as useful agents against neurodegenerative disorders such as Parkinson s or Alzheimer s diseases [42], Despite impressive clinical successes, clinical use of tranylcypromine and other MAO inhibitors is limited by various problems, including the cheese effect discussed in Section 1,... 

Lignin in the true middle lamella of wood is a random three-dimensional network polymer comprised of phenylpropane monomers linked together in different ways. Lignin in the secondary wall is a nonrandom two-dimensional network polymer. The chemical structure of the monomers and linkages which constitute these networks differ in different morphological regions (middle lamella vs. secondary wall), different types of cell (vessels vs. fibers), and different types of wood (softwoods vs. hardwoods). When wood is delignified, the properties of the macromolecules made soluble reflect the properties of the network from which they are derived. 

The lignans are a large group of plant phenolics, biosynthesized from the union of two phenylpropane molecules e.g., both matairesinol (Centaurea species, family Asteraceae) and podophyllotoxin Podophyllum peltatum, family Berberidaceae) are formed from the phenylpropane coniferyl alcohol. Lignans are essentially cinnamoyl alcohol dimers, though further cyclization and other structural modifications result in various structural types, e.g. dibenzylbutyrolactone and epoxy lignan. 

Steric effects in the alkene structure also affect linearity. As a result, quaternary carbon atoms are rarely formed in hydroformylation45 In contrast, electronic effects in hydroformylation of arylalkenes often result in the predominant formation of the branched aldehyde.6 40 43 46- 8 Styrene has a marked tendency to form 2-phenylpropanal when hydroformylated in the presence of rhodium catalysts. Rhodium complexes modified by biphosphine49 or mixed amino phosphine oxide ligands50 were shown to give the branched aldehyde with high reactivity and selectivity (iso normal ratios <61.5). 

The hexahydropyrimidine (58), formed from l-phenylpropane-l,2-dione and propane-1,3-diamine, is an excellent precursor for the a-diimine macrocyclic complexes (60), presumably via the amino ketone (59) (Scheme 36).126 In this case, intramolecular cyclization of (59) to (58) is reversible, so that the metal ion can exert a thermodynamic template effect in formation of the complex (60). This represents a further example of a long-known phenomenon in which a metal ion can stabilize an a-diimine structure by virtue of the formation of stable five-membered chelate rings. Many 2-hydroxy- or 2-mercapto-amines undergo reaction with a-dicarbonyl compounds to yield heterocyclic compounds rather than a-diimines. However, in the presence of suitable metal... 

Phenylcoumarone (VIII) has a characteristic ultraviolet and ioniza-tion-Ae spectrum, which enabled us to detect dimeric structures of this type in reaction mixtures obtained when Bjorkman spruce lignin was subjected to acidolysis for 20 hours. From the spectrophotometric estimation of the amount of the phenylcoumarone systems formed, we concluded that from a total of 100 phenylpropane units of Bjorkman lignin, about 20 are involved in phenylcoumaran systems (I) in other words, about every 10th phenylpropane unit is linked to one of its neighbors by the cyclic benzyl aryl ether linkage characteristic of I. 

Asinger s studies demonstrated that product formation is sensitive to the ratio of sulfur to ketone (1), the structure of the ketone, the replacement of ammonia by amines, the temperature and the medium. Room temperature (20-25 °C) reactions in which the ratio of sulfur to ketones is 0.5 favors the formation of 3-thiazoline, 2, as shown in Figure 1. The formation of 5-alkylidene-3-thiazolines, 3, sometimes competes with the formation of 3-thiazolines such is the case when aryl ketones such as l-phenylpropan-2-one and l-phenylbutan-2-one are employed (4). Also the additional presence of hydrogen sulfide promotes the generation of 1,2,4-trithiolanes and 1,2,4,5-tetrathiolanes from ketones ana aldehydes at the expense of 3-thiazoline formation (11-12). Increasing the S/ketone ratio to 8 favors the formation of the 3-imidazoline-5-thione (5), a product which has a greater tendency to result from aryl methyl ketones (3). 

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