X-ray-crystallography, and

In superacidic media, the carbocationic iatermediates, which were long postulated to exist duting Friedel-Crafts type reactions (9—11) can be observed, and even isolated as salts. The stmctures of these carbocations have been studied ia high acidity—low nucleophilicity solvent systems usiag spectroscopic methods such as nmr, ir, Raman, esr, and x-ray crystallography. 

Pikromycin. Pikromycin (19, R = OH, R = H), the first macroHde discovered (77,78), is produced by S.felleus. Pikromycin is identical to amaromycin and albomycetin (79—81) and may be identical to proactinomycin (82—84). The stmcture of pikromycin was deterrnined from chemical degradation, mass spectrometry, nmr, and x-ray crystallography (85—90). Its aglycone, pikronoHde (20, R = OH), was produced by S. vene elae (36). A derivative, kromycin (22, R = OH), was formed from pikromycin under acidic conditions (87,88,91) and more drastic conditions produced an intramolecular spHoketal of pikronoHde named kromin (89,91). 10,11 -Oihydropikromycin (21, R = OH, R = H), was also produced by S. vene elae (92). 

Bushman, F.D., et al. Ethylation interference and x-ray crystallography identify similar interactions between 434 repressor and operator. Nature 316 6S1-6S3,... 

An interesting example of desmotropy (cf. Chapter 1, Section V,D,2) has been reported for dihydropurines 2a and 2b both tautomers have been fully characterized by and NMR spectroscopy and X-ray crystallography [94JCS(P2)1949]. 

Fig. 3.3 H NMR and X-ray crystallography study of the bis-ether complex 28. [Denmark, S.E. Edwards, ).P. Wilson, S.R.J. Am. Chem. Soc. 1992, 114, 2592. Reprinted with permission from The American Chemical Society]...

The 2 1 reaction of 9-BBN with a series of dicarboxylic acids, namely oxalic acid, malonic acid, 2,2-dimethylmalonic acid, and succinic acid, in dimeth-oxyethane gives in some cases dimeric and in other cases macrocyclic (acyloxy)diorganoboranes. This has been proved by IR spectroscopy (all C = O groups are bidentate), B-NMR 5 = 10 ppm) and X-ray crystallography [47]. With oxalic acid two structures are possible (IV and V), of which the first with a five-membered boron heterocycle instead of a four-membered one is the more probable formulation (Fig. 13). 

A recent development in understanding the reactivity of bases has focused on their structures in solution and in the crystalline state. Due to the importance of dialkyl amide bases, there is a significant body of work, led by Williard and Collum , that has attempted to understand the structures of these reactive molecules. It is clear that they are aggregates. Lithium diisopropylamide (LiN/-Pr2) was isolated from a THF solution and X-ray crystallography revealed a dimeric structure (13 R = i-Pr, S = THF) in the... 

In addition, the [NiFe] hydrogenase from D. fructosovorans is very similar to D. gigas hydrogenase, and its structure has been solved 185). In order to understand the role of the [3Fe-4S] cluster, a Pro-432Cys mutant was produced. In this mutant the conversion of a [3Fe-4S] into a [4Fe-4S] center was proven by EPR and X-ray crystallography. 

Structural Studies of Peptoids with Aliphatic Side Chains by CD, NMR, and X-ray Crystallography... 

Chiral-at-metal cations can themselves serve as chirality inducers. For example, optically pure Ru[(bipy)3] proved to be an excellent chiral auxihary for the stereoselective preparation of optically active 3D anionic networks [M(II)Cr(III)(oxalate)3]- n (with M = Mn, Ni), which display interesting magnetic properties. In these networks all of the metalhc centers have the same configuration, z or yl, as the template cation, as shown by CD spectroscopy and X-ray crystallography [43]. 

Schering Plough has reported the discovery of the first non-hydroxamic acid containing natural product inhibitors of PDF. Sch 382582 (41) and Sch 382583 (42) were isolated from a fermentation broth of Streptomyces sp., and the proposed structures of these compoimds were derived from a combination of two-dimensional NMR studies (NOESY, HMBC and HMQC-TOCSY) and X-ray crystallography studies [116]. The proposed structure... 

Gooley PR, O Connell JF, Marcy AI, Cuca GC, Hagmann WK, Caldwell CG, Axel MG, Becker JW. Comparison of the structure of human recombinant short form stromelysin by multidimensional heteronuclear NMR and X-ray crystallography. J Biomol NMR 1996 7 8-28. 

A study of sequential Arbuzov-type demethylation reactions of the platinum(II)-phosphite complex [Pt P(OMe)3 4]2+, in which the phosphite ligands are converted to phosphonates, has been described.285 Many of the products of the reaction were characterized by NMR spectroscopy and X-ray crystallography.286 The X-ray structures are the first reported for trialkylphosphite complexes of platinum(II). 

Thus solid state NMR can be considered as a (potential) bridge between solution NMR and X-ray crystallography. 

The [l,3]oxazino[4,3- ][l,3]oxazine 387 was obtained as the main product of a combined Asinger and Ugi multi-component reaction from MeOH, NH3, 2,2-dimethyl-3-hydroxypropanal, allyl isocyanate, and C02 in 40% yield. As shown by NMR spectroscopy and X-ray crystallography, 387 is formed as a single diastereomer <1998ACS107>. 

Reaction of the 2-aminooxazoline 160 with the piperidinone 161 under basic conditions gives a mixture of linear and angular oxazolopyridopyrimidines, 162 and 163, the stmctures of which were confirmed by nuclear magnetic resonance (NMR) and X-ray crystallography of some derivatives (Equation 40) <1999T12819>. 

Two polymorphs of (/q-penicillaminc are known [2], with the existence of these being confirmed using infrared spectroscopy and X-ray crystallography. It was reported that Form I has a minimum between its IR peaks at 1078 and 1101 cm-1 that are less intense than the adjacent peaks at about 1050 and 1160 cm-1, while Form II has an absorption peak at 1092 cm-1 which is more intense than the adjacent peaks at about 1050 and 10160 cm 1 [2],... 

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