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Various kinds of Michael acceptors could be introduced at the C13²-position in an epimeric mixture of methyl pheophorbides-$a$/$a$’ under basic conditions. The isolated yields and C13²-epimeric ratios ($R$/$S$ > 1) of the adducts depended on the electron-withdrawing group in the Michael acceptors. Some Michael acceptors possessing a less electron-withdrawing group could not react with methyl pheophorbides-$a$/$a$’. Neither α- nor β-substituted Michael acceptors gave the desired products. On the other hand, a Michael acceptor possessing a terminal alkyne was introduced as the C13²-alkenyl moiety. We here report the scope and limitations of the Michael addition reactions for chlorophyll-$a$ derivatives.

The McMurry crossed coupling reactions of p,p′-disubstituted benzophenones (1) with pivalaldehyde (Pv) gave the corresponding ethenes (2) in fair to excellent yield. The observed geometrical selectivity is varied depending on a kind of p-substituent of the aromatic moiety of 1, when p′-substituent is limited to methyl. According to the known reaction mechanism, the reason why the geometry selection occurred is discussed by a conformational analysis of a possible intermediate, titanium bound pinacolate, and molecular orbital calculations of the starting carbonyl compounds. As a result, the selection is caused by electronic and stereochemical structures of anion radical of 1 and approaching mode of Pv anion radical to them. Distribution of a spin density and unsymmetrical nature of two aromatic moieties of anion radical of 1 provide predetermined pathway to bring about the pinacolate without any rotational conversion under the reaction conditions. Subsequent workup affords 2 with the observed geometry.

The conversion of glycerol to acrolein is an undesirable event in whisky production, caused by infection of the broth with Klebsiella pneumoniae. This organism uses glycerol dehydratase to transform glycerol into 3-hydroxypropanal, which affords acrolein on distillation. The enzyme requires adenosylcobalamin (coenzyme B₁₂) as cofactor and a monovalent cation (e.g. K⁺). Diol dehydratase is a similar enzyme that converts 1,2-diols (C₂-C₄) including glycerol into an aldehyde and water. The subtle stereochemical features of these enzymes are exemplified by propane-1,2-diol: both enantiomers are substrates but different hydrogen and oxygen atoms are abstracted. The mechanism of action of the dehydratases has been elucidated by protein crystallography and ab initio molecular orbital calculations, aided by stereochemical and model studies. The 5'-deoxyadenosyl (adenosyl) radical from homolysis of the coenzyme's Co-C σ-bond abstracts a specific hydrogen atom from C-1 of diol substrate giving a substrate radical that rearranges to a product radical by 1,2-shift of hydroxyl from C-2 to C-1. The rearrangement mechanism involves an acid-base 'push-pull' in which migration of OH is facilitated by partial protonation by Hisα143, synergistically assisted by partial deprotonation of the non-migrating (C-1) OH by the carboxylate of Gluα170. The active site K⁺ ion holds the two hydroxyl groups in the correct conformation, whilst not significantly contributing to catalysis. Recently, diol dehydratases not dependent on coenzyme B₁₂ have been discovered. These enzymes utilize the same kind of diol radical chemistry as the coenzyme B₁₂-dependent enzymes and they also use the adenosyl radical as initiator, but this is generated from S-adenosylmethionine.

The use of a high-field NMR instrument (ν(¹H) = 500 MHz) and 2-dimensional NMR techniques (HMQC, HMBC, ROESY) enabled us to fully assign the ¹H and ¹³C chemical shifts of bonellin dimethyl ester. The β-pyrrolic proton of C-3 appeared as a broad singlet at δ = 8.93, whereas that of C-8 gave a quartet with δ = 8.69 and ⁴J_H-H = |1.28| Hz. The C-2¹ methyl protons appeared as a doublet with δ = 3.55 and ⁴J_H-H = |1.07| Hz, while the C-7¹ methyl protons afforded a doublet with δ = 3.51 and ⁴J_H-H = |1.28| Hz. These results suggest that the β-pyrrolic carbons of ring A belong to the aromatic 18 π-electron [18]diazaannulene delocalization pathway, whereas those of ring B remain outside the aromatic pathway. The broadening of the C-3 β-pyrrolic proton signal can be attributed to the allylic 3-CH - 2¹-CH₃ coupling and the 3-CH - 21-NH coupling. At 330 K, the tautomeric exchange 21-NH_a ⇌ 23-NH_b is fast and only one broad signal at δ = -2.49 is seen for these protons. The ROESY spectrum showed clear correlation signals between the 18²-CH₃ and 17¹-CH₂ protons, the 18²-CH₃ and 17⁴-CH₃ protons, as well as between the 18¹-CH₃ and 17-CH protons. These results are compatible with the previous assignment that the absolute configuration at C-17 is S. Application of spin simulation enabled us to determine the chemical shifts and the ³J_H-H coupling constants of the 17-propionate side-chain. The ³J_H-H-values were used to calculate the populations for the 17¹-17 and 17²-17¹ rotamers. A relatively high population value of 0.41 was found for the 17¹-17 g^--rotamer, whose methoxycarbonylmethyl group points to the C-15 methine-bridge. This was interpreted as explaining the high tendency of bonellin to form anhydrobonellin. The rotational freedoms in the 13-propionate side-chain were studied by measuring the ¹H NMR spectra of the side-chain at temperatures between 300 and 195 K. At 300 K, the 13¹- and 13²-CH₂ proton signals appeared as deceptively simple triplets, which at 195 K were split into complex multiplets. At 195 K, the signal arising from the 13¹-CH₂ protons exhibited more splitting, which indicates that these protons have less rotational freedom than the 13²-CH₂ protons.

The aggregation of a tetraaryl-porphyrin with chiral amide-containing side groups depends critically on the central metal ion in the tetrapyrrolic core, an effect shown dramatically in solution as well as in the gel formation by the compounds. In solution, the circular dichroism (CD) spectra of the metalloporphyrins show that they all aggregate to some degree, and in most cases the aggregates of the metal-containing species is more favored than the parent free-base porphyrin. The compound which shows the greatest optical activity is the zinc(II) porphyrin which forms a J-aggregate with large Cotton effects in the CD spectrum. Infrared spectroscopy revealed that this aggregate is favored by interaction of the amide oxygen atom with the zinc(II) ion at the core of the porphyrin. The other metalloporphyrins, containing divalent copper, cobalt, and palladium or manganese(III) acetate all show CD activity, and all but the cobalt compound form gels in hexane or cyclohexane. The morphology of the xerogels formed after evaporation of the solvent from these gels depend greatly on the metal ion, with only the copper porphyrin — which shows a clear H-aggregate in solution — having a fibrous morphology

“What do you want to be when you grow up?” is a common question posed to children, and answers such as firefighter, policeman, athlete, doctor, or teacher are probably just as common. Some, like Oliver Sacks, recall an early fascination with metals, the periodic table, and chemical reactions that planted the seeds for the later pursuit of the natural sciences or medicine (neurology in his case). We are familiar with memories of chemists that include their first chemistry set, followed by complaints by parents over strange smells and close calls due to particularly exothermic reactions. For others, including myself, a future in research remained more obscure until a later period in adolescence or perhaps even the undergraduate years. Rather than seeking out a field, the field finds you. In actuality, teachers and mentors with expertise in and enthusiasm for a field exert a force that charts a path toward scientific research throughout life. Here, I stress the importance of terrific teachers and mentors from high school onwards to the undergraduate, Ph.D., and postdoc years for setting me on a track (and on occasion preventing me from derailing) to research in structural chemistry and molecular mechanism using crystallography as the main tool.

Almost half of biological molecules (proteins and metabolites) are extrapolated as glycosylated within cells. Detection of glycosylation patterns and of attached sugar types is therefore an important step in future glycomics research. We present two algorithms to detect sugar types in Haworth projection, i.e., from x-y coordinates. The algorithms were applied to the database of flavonoid and identified backbone-specific biases of sugar types and their conjugated positions. The algorithms contribute not only to bridge between polysaccharide databases and pathway databases, but also to detect structural errors in metabolic databases.

The chirality (of Greek χείρ, ch[e]ir: hand) is a fundamental symmetry property of three-dimensional objects. Your two hands are not superimposable. They are mirror images of each other. They are therefore chiral (Figure 10.1). The chirality of your right hand can be seen by trying to put it in a glove for your left hand. The same can be seen by trying to put your left hand into a glove for your right hand. The same experience can be done while putting on shoes. Normally you are not comfortable after exchanging the shoe for the left foot with the one for the right foot…