Stereospecific deuteration

Although there is usually a preference for anti elimination in acyclic systems, syn elimination is competitive in some cases. In acyclic systems, the extent of anti versus syn elimination can be determined by use of stereospecifically deuterated substrates or by use of diastereomeric reactants which will give different products by syn and anti elimination. The latter approach showed that elimination from 3-phenyl-2-butyl tosylate is a stereospecific anti process. ... 

In order to assess the influence of the heteroatom on vicinal coupling constants, several stereospecifically deuterated tetrahydropyrans have been synthesized (76JOC1380). 

Stereospecific deuteration of the substrate for enolase, the enzyme that makes phosphoenol pyruvate, gives the results shown... 

Fig. 14. Stereospecifically deuterated ethylene glycols which were tested on dioldehydratase.

Products obtained from stereospecifically deuterated ethylmalonyl-CoA species... 

A. Carbene or Carbenoid Addition to Stereospecifically Deuterated Alkenes... 

The above mechanisms for cis-1,4 polymerization of isoprene or isotactic polymerization of acrylates assume that the configuration of each unit is fixed at the moment of reaction and that no racemization occurs between additions of monomer molecules. Little evidence for the validity of the mechanisms was available when suggested. Recently it has been possible to obtain information, from NMR studies, on the reaction path. This evidence is of two types and depends on the polymerization of stereospecifically deuterated monomers to determine the mode of approach of monomer molecules and on direct observations of NMR spectra of the terminal monomer unit in the polymer. 

Electrochemical oxidation of stereospecifically deuterated titanacyclobutanes 17 or reaction with tetrakis(trifluoromethyl)cyclopentadienone (TTFC), 2,3-dichloro-5,6-dicyano-l,4-ben-zoquinone (DDQ) or ferricinium ion leads to stereospecific formation of cyclopropanes with a high degree of retention of configuration. ... 

The bulk of the KIE studies with SLO have used substrate that is dideuterated at the C-11 position. In order to differentiate the impact of deuteration on the cleaved [11,S] vs. the noncleaved position [11,1 ], stereospecifically deuterated [11,S- H] -linoleic acid was synthesized. Analysis of enzyme kinetics using either WT- or mutant forms of the enzyme initially yielded anomalously large secondary KIEs. This was subsequently shown, by mass spectrometric analysis of the enzymatic product, to be due to a loss of stereochemistry at C-11, arising, in fact, from the enormous KIE at the primary position. Through a combination of kinetic and mass spectrometric analyses, it could be shown that the bulk of the observed KIE with dideuterated substrate arises from the primary position, °[kintrinsk(l°)] =75 and °[kintrinsic(2°)] = 1.1 [79]. 

Alanine racemase is a bacterial enzyme that catalyzes racemization of l- and d-alanine, and requires pyridoxal 5 -phosphate (PLP) as a cofactor. The enzyme plays an important role in the bacterial growth by providing D-alanine, a central molecule in the peptidoglycan assembly and cross-linking, and has been purified from various sources15 161. The enzyme has been used for the production of stereospecifically deuterated NADH and various D-amino acids by combination of L-alanine dehydrogenase (E. C. 1.4.1.1), D-amino acid aminotransferase (E. C. 2.6.1.21), and formate dehydrogenase (E.C. 1.2.1.2)I17, 18. ... 

By using a stereospecifically deuterated substrate, it can be shown that the cpimcrization 15 16 and the rearrangement to and from 17 mainly occurs by a series of suprafactal [1,5] sigmatropic hydrogen shifts via a common isoindene-type intermediate 15a (cf. 9)26. 

In principle, isotopic labeling ought to permit the neutral products of a cationic reaction to be deduced from mass spectrometric measurements alone. As an example, the elimination reaction drawn in Scheme 1 yields a mixture of cis and trans alkenes when the alkyl group has >3 carbons. If the reaction passes through transition state drawn in Scheme 1 (called a syn-transition state), the ratio of alkene isomers from the stereospecifically deuterated precursors in Scheme 4 should correspond to the ratio of PhOH " to PhOD " observed in the mass spectrum. 

The extent of syn elimination in 5-decyl systems was measured using diastereomeric deuterium-labeled substrates. Stereospecifically deuterated 5-substituted decane derivatives were prepared and subjected to various eiimination conditions. By comparison of the amount of deuterium in the E- and Z-isomers of the product, it is possible to determine the extent of syn and anti elimination. ... 

Table 5 reveals the products of substrates which have been deuterated in H20. In other cases deuterated enoates were reduced in H2O. The reductions in H20 lead to acylates with two chiral carbon atoms due to stereospecific deuteration of methylene groups. Most of these have been used in studies of biosynthetic pathways of natural products. For examples see (29,30). Reactions in H20 proceed usually slower than in H2O. The differences may be less than a factor 2 if optimal pH and p H values are determined and applied. The p H and pH value for optimal reaction rates are not the same (31). 

Stereospecific deuterations of 2-enoates (14,15,29,30,40) have to be carried out in H20 buffer with freeze dried cells (Table 5). Freeze drying under exclusion of oxygen leads to cells without loss of enzyme activity if again under anaerobic conditions 1 g wet packed cells is slowly stirred or shaken with 0,5 ml of a 10 pM solution of potassimn hexacyanoferrate-III for 20 minutes at 35 C. Under these conditions enoate reductase and probably also hydrogenase are transferred into the oxidized state. 

The enzyme tryptophan synthase (EC 4.2.1.20) catalyzes the reaction of serine 60 with indole 92 give the amino acid tryptophan 93 as shown in Scheme 27. Fuganti etal. (88) used this enzyme to convert samples of stereospecifically deuterated serine, prepared as in Scheme 19, to labeled samples of tryptophan 93. These were shown to have the stereochemistry... 

Serine is the precursor of several antibiotics. The oxazole ring of the antibiotic virginiamycin Mj 100(Scheme 31)is derived from serine incubation of Streptomyces virginiae with samples of (2S, 3R)- and (2S, 3S)-[3- Hi]serine, derived as in Scheme 18, showed that the 3-pro-S hydrogen of serine is lost on formation of the double bond (107). This implies anti dehydrogenation, a process more commonly found to be syn. The -lactam antibiotic nocardicin 101 is biosynthesized from serine, and incubation of Nocardia uniformis with stereospecifically deuterated serines, prepared by the method outlined in Scheme 21, has yielded samples of norcardicin, the NMR spectra of which indicated that ) -lactam ring formation occurs with inversion of configuration (108, 109). 

More recently, Baldwin etal. (136) prepared samples of stereospecifically deuterated DL-cysteine by the method outlined in Scheme 43, and converted these to diastereomeric tripeptides that could be separated. It is of interest that the azide substitution 139- 140 occurs with retention of configuration in this synthesis. 

Tyrosine phenol lyase (EC 4.1.99.2), which will reversibly break down tyrosine 298b to phenol, pyruvate 145a, and ammonia, also catalyzes the ) -replacement reaction of tyrosine 298b with pyrocatechol 315 to yield dihydroxyphenylalanine (DOPA) 316. By using stereospecifically deuterated samples of tyrosine 298b and assessing the configuration of the DOPA... 

Mosberg, H.L, Sobczyk-Kojiro, K., Subramanian, P., Crippen, G.M., Ram alingam, K. and Woodard, R.W. (1990) Combined use of stereospecific deuteration, NMR, distance geometry, and energy minimization for the conformational analysis of the highly 8 opioid receptor selective peptide [D-Pen, D-Pen ]enkephalin. J. Am. Chem. Soc. 112 822-829. 

Coke et have challenged the Sicher-Zavada generalisation that cis-cycloalkenes are derived from a/m-elimination and tra/i -cycloalkenes from 5y -elimination. They agree with the latter deduction but regard m-cyclo-alkene formation as more complex, arising from both syn- and a/iti-elimination. The m-olefins were analysed from the Hofmann degradation of alicyclic stereospecifically deuterated trimethylammonium hydroxides, viz. 

The cyclization step requires Lewis acid catalysis lithium chloride, formed during an attempt at silylation, is sufficient. The stereochemical course under these conditions (retention at the carbanionic center, inversion at C-3) was rigorously proven by stereospecific deuteration, and an X-ray structure analysis of amino ketone 171, as well [57]. Surprisingly, the use of the stronger Lewis acids f-BuMe2SiOTf or Bp3-OEt2 caused the formation of the opposite enantiomer ent-169 [57] the reasons are still unknown. The cyclopropanes 169 are easily depro-tonated by sec-butyllithium/TMEDA and substituted by many electrophiles with complete retention [57]. The reactions are quite general diastereomers are formed from 2-monosubstituted dicarbamates [108]. 

A mechanism for the stereospecific monodeuteration of tricarbonyl(l-car-bomethoxycyclohexa- ,3-diene)iron [Eq. (129)] is suggested in Scheme 11. This mechanism is consistent with all the available data on stereospecific deuterations of variously substituted tricarbonyl(cyclohexadiene)iron complexes (A. J. Birch, B. J. Chauncy, and D. J. Thompson, unpublished results, 1975) and with the large D/H (deuterium/hydrogen) isotope effect, i.e., ratedetermining protonation at Fe (Whitesides and Nielan, 1975). It should be noted that the principle of microscopic reversibility may not strictly apply in... 

One example of a stereospecific deuteration on the side of the molecule opposite the tricarbonyliron group has been observed [Eq. (132) (Hunt et al.. 

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