Structure of macrocyclic alkaloids, oncinotin and isoocinotin

Two new macrocyclic alkaloids oncinotine ( 1 ) and isooncinotine ( 2 ) have been isolated from Oncinotis nitida BENTH . 1 can be converted into 2 by an amide exchange reaction. The spermidine residue was present in both bases. The structural elucidation was based mainly on (I) the determination of the functional groups, (II) degradation to compounds 12 and 13 and (III) mass spectrometric investigation of 1 and of the above mentioned degradation products.     

Voltammetry in ammonium fluoride solution with particular reference to manganese

The voltammetric behaviour of 19 ions in 1M ammonium fluoride solution has been investigated, using a rotating platinum electrode. In this base electrolyte, manganese(II) is oxidised reversibly to manganese(IV) at + 0.52 V vs. S.C.E. and this reaction has formed the basis for a simple voltammetric method for the determination of steels and cast iron of low cobalt content.     

Synthesis of Antipyrine Derivatives Derived from Dimedone

Coupling of dimedone with the diazonium salt of 4-aminoantipyrine afforded 2,3-dimethyl-4-[2-（5,5-dimethyl- 2,6-dioxocyclohex-2-ylidend）-hydrazino]-5-oxo-1-phenylpyrazoline （3）. Reaction of 3 with excess phenylhydrazine gave the mixed trishydrazone derivative 4. Treatment of 3 with hydroxylamine produced the bisoxime 5 which upon dehydrative cyclization with acetic anhydride gave the corrsponding tetrahydrobenzo[d][1,2,3]triazole derivative 7. A one-pot synthesis of 7 was done by reacting 3 with hydroxylamine hydrochloride in pyridine, followed by heatment with acetic anhydride.     

FROM A SYSTEMIC APPROACH IN TEACHING AND LEARNING CHEMISTRY（SATLC）TO BENIGN ANALYSIS

The Systemic Approach in Teaching and Learning Chemistry (SATLC)was established in 1997^[1-3].Our interest in developing the SATL strategy arose from the recognition of the increasing globalization of a wide specturm of human activities such as economics,media,politics,and entertainment,Systemics is our attempt to provide the student with a global view of his/her studies of chemistry.     

The reaction of isothiocyanates with 2-cyanoethanoic acid hydrazide. A novel synthesis of 1,3,4-thiadiazoles

Benzoyl and ethoxycarbonyl isothiocyanates reacted with 2-cyanoethanoic acid hydrazide 2 to afford 1-cyanoacetyl-4-substituted thiosemicarbazide ( 5a,b ). Compound 5a afforded the pyrazolo[1,5-a]-s-triazine derivative 6 on treatment with 5% potassium hydroxide, and cyclised to 2-benzoylamino-5-cyanomethyl-1,3,4-thiadiazole ( 8 ) when boiled under reflux in glacial acetic acid. Compound 8 condensed with aromatic aldehydes to yield the corresponding arylidene derivatives 9a-c . It undergoes coupling with aromatic diazonium salts to afford the hydrazones 11a-c . Similarly, it coupled with diazotised aminopyrazole to afford the cyclic product 12 .     

Reactions with heterocyclic diazonium salts: New routes for the synthesis of pyrazolo[1,5-c]-1,2,4-triazoles and pyrazolo[1,5-c]-as-triazines

3-Phenylpyrazole-5-(liazonium chloride ( 1 ) couples with α-chloro derivatives of acetylacetone, ethyl acetoacetate and aceto-o-anisidine to yield the corresponding pyrazole-5-yl hydrazonyl chloride derivatives 2a-c . Compounds 2a,b were cyclised to yield either the pyrazolo[1,5-c]-1,2,4-triazole derivatives 3a,b or the pyrazolo[1,5-c]-as-triazines 4a,b depending on the applied reaction conditions. Compound 2c cyclised only into 3c under different cyclization conditions. The pyrazolo[1,5-c]-as-triazine derivatives 4c-e could be prepared via condensation of 2a with potassium cyanide. Compound 2d reacted with aromatic thioles and with sodium benzene-sulphonate to yield the pyrazolo[1,5-c]-as-triazine derivatives 6a-d . Compound 1 reacted with activated double bond systems to yield pyrazolo[1,5-c]-as-triazines 8a,b and 9 .     

The profound influence of a single metal-carbon bond on the reactivity of bio-relevant cobalt(III) complexes

This Perspective reports the development of mechanistic insight over the past 6 years, on the substitution behaviour of cobalamins that contain a single Co-C bond. The effect of the alkyl group, located in the trans position, on the thermodynamic, kinetic and ground state trans effect, was studied in detail. The substitution reactions of different alkylcobalamins with CN- were investigated, the apparent mechanistic discrepancy reported for the co-enzyme B12 was resolved and a logical explanation could be offered. In addition, a complete picture of the effect of pressure on the UV-Vis spectra of different base-on and base-off cobalamins is presented, which clearly shows the role of the alkyl group in controlling the equilibrium between five- and six-coordinate species, and the possible participation of such species in the studied ligand substitution reactions. The kinetics of the base-on/base-off equilibration was studied for the first time using a pH-jump technique. All in all the novel mechanistic information adds to the understanding of the profound effect that a single metal-carbon bond can have on the reactivity of such Co(III) complexes.     

Reactions with heterocyclic β-enaminoesters: A novel synthesis of 2-amino-3-ethoxycarbonyl-(4H)-pyrans

The reaction of ethyl cyanoacetate with -cyanochalcone (1) leads to the formation of -enaminoesters (3) viaMichael addition. Compound3 reacts with phenylmagnesium bromide to give the -enaminoketone5. Acetylation of3 gives the acetyl product4. Each of compounds1 and3 reacts with malononitrile to give -enaminonitrile6. Phenylhydrazine reacts with3 to give the hydrazone7. Similarly 3-phenyl-5-aminopyrazole reacts with3 to give theSchiff base8.

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Reaktionen mit heterocyclischen -Enaminoestern: Eine neue Synthese von 2-Amino-3-ethoxycarbonyl-(4H)-pyranen

Zusammenfassung Die Reaktion von Ethylcyanacetat mit -Cyanchalcon1 führt über eineMichael-Addition zum -Enaminoester3.3 gibt mit Phenylmagnesiumbromid das -Enaminoketon5. Acetylierung von3 gibt das Acetylderivat4.1 und3 reagieren mit Malodinitril zum -Enaminonitril6.3 gibt mit Phenylhydrazin das Hydrazon7; 3-Phenyl-5-aminopyrazol reagiert mit3 zurSchiff-Base8.

     

Simple chromatogaphic method for the separation and estimation of gibberellic acid in crude products

Summary The estimation of gibberellic acid by a direct spectrophotometric method is described. For the separation a paper-chromatographic technique is used with a modified solvent and with a colour reaction of alkaline permanganate. Comparative data proved that the new method is superior to other techniques and can be applied to pure gibberellic acid or crude preparations as no interference occurs after chromatographic separation.

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Zusammenfassung Zur Bestimmung der Gibberellinsäure wird eine spektralphotometrische Methode angegeben. Dabei wird zunächst papierchromatographisch abgetrennt und dann eine Farbreaktion mit alkalischem Permanganat ausgewertet. Die Methode, die früheren überlegen ist, kann zur Bestimmung von Gibberellinsäure in reinen Produkten sowie in Rohprodukten verwendet werden.