Carbon-13 nuclear magnetic resonance spectra. VIII—18α- and 18β-glycyrrhetic acid derivatives

The ¹³C NMR data of six pairs of 18α/18β-glycyrrhetic acid derivatives are presented. It is shown that the configuration at C-18 can easily be recognized by inspecting the chemical shifts of several characteristic carbons, e.g. C-12, C-13, C-18 and C-28. The shifts of these carbons originated by the change of the D/E ring junction proved to be largely independent of the substitution at C-3 and C-20.     

The synthesis of β-heteroarylamino-α,β-dehydro-α-amino acid and β-heteroarylamino-α-amino acid derivatives

From heteroarylaminomethyleneoxazolones 4 , obtained from N-heteroarylformamidines 2 and 2-phenyl-5-oxo-4,5-dihydro-1,3-oxazole ( 3 ), the following β-heteroarylamino-α,β-dehydro-α-amino acid derivatives were prepared: methyl 8 and ethyl esters 9 , amides 10 and 11 , hydrazides 12 , and azides 15 . By catalytic hydrogenation the compounds 4 were converted into β-heteroarylamino substituted amides 18 and β-heteroarylamino-α-amino acids 20 .     

Studies on furan derivatives IV. A simple preparation of α-substituted β-(5-nitro-2-furyl)ethynyls from α-substituted β-(5-nitro-2-furyl)vinylamines

α-Substituted β-(5-nitro-2-furyl)ethynyls were conveniently prepared by the deamination of α-substituted β-(5-nitro-2-furyl)vinylamines. Also the application of this reaction toward α,β-bis(p-nitrophenyl)vinylamine was examined and afforded α,β-bis(p-nitrophenyl)ethynyl as the main product.     

Mass spectrometry and organic analysis—XII αβ-Unsaturated secondary alcohols

The fact that some αβ-unsaturated alcohols give mass spectra that bear some similarity with the corresponding saturated ketones is discussed, and the double hydrogen transfer necessary to accommodate this is examined by deuterium labelling.     

Four-center type photopolymerization in the solid state. IV. Polymerization of α,α′-dicyano-p-benzenediacrylic acid its derivatives

The solid-state photopolymerization of α,α′-dicyano-p-benzene diacrylic acid (p-CBA) series has been studied. p-CBA, its esters, amide, and a few other cyano derivatives were prepared and new polymers were obtained from p-CBA alkyl esters on irradiation of ultraviolet or visible light. Though the polymerization behavior differs with each monomer, polymerization proceeds in essentially the same manner as in the 2,5-distyrylpyrazine (DSP) and p-benzenediacrylic acid (BDA) series: the reaction proceeds topochemically forming polymer with a cyclobutane ring in the main chain. Properties of high polymer are typical of cyclobutane-containing polymer. That is, they are highly crystalline with high melting temperature and a limited solubility. The study on this series of compounds, as well as the DSP and p-BDA series, supports the generalization that solid-state dimerization can be extended to solid-state photopolymerization of compound having two dimerizable units in a molecule.     

The synthesis of β-heteroarylamino-α,β-dehydro-α-amino acid derivatives via thiazolones

2-Alkoxy-4-heteroarylaminomethylene-5(4H)-thiazolones 4 were converted with various nucleophiles into β-heteroarylamino-α,β-dehydro-α-amino acid derivatives 11, 14, 15, 16, 17, 18 , and 19 . Reduction of 4 with sodium borohydride in ethanol saturated with gaseous ammonia afforded the corresponding β-heteroaryl-amino substituted alanyl amides 20 . Thiazoledione derivative 7a was transformed with sodium methoxide in methanol into 1-(4,6-dimethylpyrimidinyl-2)-4-mercaptocarbonylimidazol-2(3H)-one ( 8a ).     

Carbon-13 NMR spectra of some pentacyclic triterpenoids with the olean-12-ene and 18α-olean-12-ene skeleton

The ¹³C NMR spectra of some pentacyclic triterpenoids, 3β-acetoxy-11-oxo-olean-12-ene-30-oic acid methyl ester, 3β-acetoxy-11-oxo-olean-12-ene-29-oic acid methyl ester, the corresponding 11-desoxo methyl esters, 3β-acetoxy-11-oxo-18α-olean-12-en-30-oic acid methyl ester and 3β-acetoxy-11-oxo-18α-olean-12-en-29-oic acid methyl ester are discussed. The shielding data are interpreted in term of the different orientation of the carbomethoxy group and of the change in configuration at the D/E ring junction and are diagnostically valuable for the differentiation of the mentioned compounds.     

Transformations of isomeric naphthopyranones. The synthesis of substituted β-naphthyl-α,β-dehydro-α-amino acid derivatives

The opening of the pyranone ring in 2H-naphtho[1,2-b]pyran-2-one derivative (1) and 3H-naphtho[2,1-b]-pyran-3-one derivatives 8 and 20 with nucleophiles afforded 3-(naphthyl-1)- and 3-(naphthyl-2)propenoates (substituted β-naphthyl-α,β-dehydro-α-amino acid derivatives) 7, 13, 14, 15, 24 , and 35 .     

Applications of 1,4-addition of grignard reagents to α,β-unsaturated acid derivatives. III—configuration studies of α,β-diaryl-α,β-dialkylpropionitriles

The configuration of twenty-four different α,β-diaryl-α,β-dialkylpropionitriles has been determined using nuclear magnetic resonance spectra. The erythro form showed greater deshielding of the methine hydrogen and alkyl groups in its spectra than the corresponding threo isomer. The former, however, showed less deshielding of the aryl groups than the threo isomer. Infrared spectra were not suitable for assignments of configuration.     

Lipophilic Functionalized Cobyrinic-Acid Derivatives. Part 1. Cobester α-monoacids (α,α,α,β,β,β-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates)

The four α,α,α, β,β,β,-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates 2b, d–f , with a free b-, d-, e-, and f-propionic-acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ-dicyanocobyrinate (cobester; 1 ) in aqueous sulfuric acid. The cobester monoacids 2b, d–f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic-acid function was determined by an extensive analysis of 2b, d–f using 2D-NMR techniques; an analysis of the C,H-coupling network topology resulted in an alternative assignment strategy for cobyrinic-acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b-isomer 2b , was also obtained in the solid state from a single-crystal X-ray analysis. Earlier structural assignments based on 1D-NMR spectra of the corresponding regioisomeric monoamides 3b, d–f (obtained from crystalline samples of the monoacids 2b, d–f ) were confirmed by the present investigations.     

Enantioselective separations by capillary GC on derivatized cyclodextrins. Part 1: Separation of some racemic 2,2-dialkyl-4-alkoxycarbonyl-1,3-dioxolane derivatives on permethylated α-, β- and γ-cyclodextrins

The enantioseparation of some 2,2-dialkyl-4-alkoxycarbonyl-1,3-dioxolane derivatives, which are important intermediates in the total synthesis of a number of biologically active compounds, was studied by means of capillary gas chromatography (CGC). The chromatographic results, obtained on columns coated with permethylated α-, β- and γ-cyclodextrin respectively, are reported. Out of sixteen compounds, thirteen could be separated with a resolution superior to 1,2. One racemate could not be separated on any of the columns. Considerations concerning the separation mechanism are proposed.     

Mass spectrometric comparison of ordinary and fully deuterated α- and β-carotene

The individual, deuterated, isomeric α- and β-carotenes were isolated from the green alga, Scenedesmus obliquus, cultivated in D₂O containing 99·7 to 99·8 atom percent deuterium. Mass spectroscopy showed that both the α- and β-deuterio-carotene preparations contained principally the fully deuterated pigment molecules (C₄₀D₅₆), small quantities of deuterated molecules with one proton (C₄₀D₅₅H) and yet smaller quantities of deuterated molecules with two protons (C₄₀D₅₄H₂). From statistical calculations the deuterio-carotene preparations also contained one to several isotopically-substituted deuterio-carotenes of each mass in the mass range 585 to 599 because of variation of the number of ¹³C and H atoms per molecule. The mass fragmentation of the deuterated pigments was analogous to that of the respective ordinary α- and β-carotene. It indicated that the protons in the C₄₀D₅₅H and C₄₀D₅₄H₂ molecules were distributed approximately randomly in various parts of the structure as in the terminal rings and in the ends and central portions of the polyene chain.     

Mass spectra of some α-substituted phenyl-α,α′-dimethoxyl ketones and their derivatives

The mass spectra of some α-substituted phenyl-α,α′-dimethoxyl ketones (compounds 1) and their 2,4-dinitrophenylhydrazones (compounds 2) and semicarbazones (compounds 3) have been studied. The characteristic fragments at m/z (M ? 73) from compounds 1, m/z (M ? 253) from compounds 2 and m/z (M ? 130) from compounds 3 are abundant and proposed to be [ArCROCH₃]⁺. Fragmentations yielding [M⁺ ? 49] from compounds 2 are abnormal and probably involve the methoxyl and nitro groups. The intense peak at m/z 130 due to [CH₃OCH₂CNNHCONH₂]⁺ from compounds 3 corresponds to α-cleavage of the molecular ion. Some other fragments from these new compounds are interpreted in this paper.