X-Ray Studies of Amino Acids and

R.B. Corey, X-ray studies of amino acids and peptides, Advan. Protein Chem. 4 385-406 (1948)... 

Aromatic side chains of amino acids such as phenylalanine, tryptophan, and tyrosine are found in general in the interior of proteins, in hydrophobic regions. In some proteins they mediate helix-helix contacts. It is to be expected that agents containing aromatic groups could interact with proteins via aromatic-aromatic interactions, as for instance, proven by X-ray studies of biphenyl compounds which inhibit sickle-cell hemoglobin gelation. 

The regio- and stereochemical outcome of the intermolecular 1,3-dipolar cycloaddition of an azomethine ylide generated by the decarboxylative condensation of an isatin with an a-amino acid was unambiguously determined by a single-crystal X-ray study of the spirocyclic heterocycle 49 (R1 =4-Br, R2 = H, X = CH2) <1998TL2235>. 

When Linus Pauling and Robert Corey carried out their pioneering X-ray crystallographic studies on a number of amino acids and dipeptides in the 1930s and 1940s, they... 

Complexes with SBs from Hsal and ar-amino acids (glycine, l- and DL-alanine, L-methionine, L-valine, L-leucine, l- and DL-phenylalanine) were prepared and characterized.786 The complexes are bluish-grey and there is no appreciable interaction between V atoms. The compounds were [VO(SB)(H20)] (111), confirmed in an X-ray study of (111 R = Me, L-Ala derivative).787 v(V=0) was at —1000 cm-1 the compounds are not soluble in noncoordinating solvents, but when dissolved in py v(V=0) shifts to —970 cm-1 several orange py adducts (112) were isolated.686 Complexes (111) have electronic spectra that resemble those of... 

Since the publication of the synthesis of ergotamine (34) all naturally occurring peptide alkaloids have been synthesized by analogous routes. Moreover, it has been shown that they all have the same stereochemistry and differ from each other only in their L-amino acid units and the chain length of the a-hydroxy-a-amino acid moiety at the peptidic site. An X-ray study of a key intermediate has provided additional evidence for the correctness of the proposed absolute configuration of ergotamine (34a). 

This topic has been thoroughly developed insofar as the conformational behaviour of amino acids and peptides in aqueous solutions is concerned. The main driving force for conformational studies has been the pharmaceutical interest in the interactions of biologically active amino acids and peptides with tissue, particularly with cell receptors. The solid-state behaviour of amino acids and peptides, though less relevant in the pharmaceutical context, has not escaped investigation. This is because of the wider distribution and greater ease of use of X-ray crystallography equipment nowadays. 

Information concerning the molecular details of steroid-protein interactions can be obtained from X-ray analysis of crystalline complexes of proteins with appropriate steroid agonists and,antagonists, and from X-ray studies of model complexes of steroids with amino acids. 

Recent X-ray studies of enzymes for which steroids are primary substrates, steroid binding globulins, and fragments of steroid receptors with amino acids and nucleic acids are just beginning to provide additional insight into the nature of steroid receptor binding and macromolecular interactions, and the mechanism by which steroids exert their hormonal functions. 

A large number of coenzyme analogs modified at various positions of the NAD molecule have been prepared and tested for coenzyme activity with LADH and YADH. The results are generally consistent with the X-ray studies of the binding of coenzyme analogs to LADH (Section II,C,3). Some analogs discussed in Sections II,E and III,C have been used to modify specific amino acid residues of the enzymes. 

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