Absolute configuration of cryptostylines I,II, and III by x-ray analysis and aromatic chirality method

The S-configuration of the alkaloids cryptostylines I, II, and III was assigned on the basis of a single crystal X-ray analysis of unnatural cryptostyline II hydrobromide (5.HBr: orthorhombic, P2₁2₁2₁a = 10·162, b = 12·352, c = 16·456 Å) and confirmed by application of the aromatic chirality method. Further evidence for the configurational assignment was provided by the CD spectra of the monophenolic derivatives of unnatural cryptostyline II (14).     

Structural determination of ascorbic acid 2-o-phosphate formed via acid hydrolysis of an ascorbic acid 3-O-phosphinate

The synthesis and X-ray structural determination of 3-O-[(bis-morpholino)phosphinyl]-5,6-O-isopropylidene-l-ascorbate (9) are described. Acid-catalyzed hydrolysis of 9 afforded the 2-O-phosphate 6. Definitive structural proof of 6 is based on a study of the pH profile of its UV spectra as compared with those of ascorbic esters, 2 and 9 (Figs. 1–3).     

Economic considerations important in the scale-up of an ovalbumin separation from hen egg-white on the anion-exchange cellulose DE92.

The scale-up of the separation of hen egg-white proteins has been investigated using Whatman DE92 anion-exchange cellulose. Having developed suitable chromatographic conditions, a maximum binding capacity of 100 mg protein/ml packed DE92 was determined in a 25-ml column. The process was scaled up 1000-fold and the influence of batch and column techniques on the chromatographic step assessed. Data indicate column processes to be more efficient than batch in the adsorptive stage.     

Nitroimidazoles II. synthesis and reactions of iodonitroimidazoles

The synthesis and some chemical reactions of various iodonitroimidazoles and methods of distinguishing between the 4- and 5- nitro derivatives by UV and pK measurements are described.     

Substituted pyrimidines. II. 1,3-Dimethylisocytosine and related compounds

1,3-Dimethyl-1,2-dihydro-2-imino-4(3H)pyrimidinone (1,3-dimethylisocytosine) was prepared by methylation of 2-amino-3-methyl-4(3H)pyrimidinone and was degraded in alkaline solution to a mixture of 3-methyl-2-methylamino-4(3H)pyrimidinone, 1,3-dimethyl-2,4-(1H,3H)pyrimid-indione, 2-methylamino-l-methyl-4(1H)pyrimidinone, 1-methyl-2,4-(1H,3H)pyrimidindione and 3-methyl-2,4-(1H,3H)pyrimidindione. Thiation of the title compound gave both 1,2-dihydro-1,3-dimethyl-2-thio-4(3H)pyrimidinone and 1,3-dimethyl-2,4-(1H,3H)pyrimidinedithione. The title compound is a tautomerically fixed pyrimidine and its uv spectra were compared with related compounds, notably 3-methyl-2-dimethylarnino-4(3H)pyrimidinone which is also tautomerically fixed.     

Chiroptical Properties of Fluorescamine Derivatives of Chiral Primary Amines in situ

Primary amines react efficiently with fluorescamine (FLURAM®) to form pyrrolinone-type chromophores with long wavelength absorption maxima at 380–410 nm. When the primary amine is chiral, these chromophoric derivatives exhibit characteristic Cotton effects. The chiroptical properties of the reaction mixtures can be related to the absolute configuration of the amines without isolation of the products.     

Solvent and pH Effects on the Sign of the ORD Spectrum of N-Methyl-4-phenyl-7-methoxy-1,2,3,4-tetrahydroisoquinoline in the Visible Spectral Range

It has been described in the literature¹ that the protonation of the nitrogen in 1-benzyl-1,2,3,4-tetraisoquinoline derivatives does not affect the sign of the ORD spectra. We have recently observed² that in the case of several (R) and (S) N-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinol ine derivatives this is true only for the three Cotton effects below 300 nm (the ¹L_b, ¹L_a and ¹B electronic transitions³ of the aromatic moiety), although appreciable variations in intensity and slight shifts in the positions of the extrema were also noticed. On the other hand, the sign of the rotation in the visible spectral range was reversed upon protonation in 0.1N methanolic HCl (or hydrochloride of 1 in methanol).     

A simple method for determining the absolute configuration of α-amino acids

Chiral α-amino acids react with 2-methoxy - 2,4 - diphenyl - 3 (2H) - furanone 1 to afford N-substituted 3,5 - diphenyl - 5 - hydroxy - 2 - pyrrolin - 4 - ones 2. The characteristic cotton effects given by these chromophoric derivatives provide a means for the determination of the absolute configuration of the parent amino acids. The longest wavelength(first) extremum in the chiroptical spectra (ORD and CD) of the l-amino acid derivatives is always positive, while it is negative for the d-amino acid derivatives.