Stereoselectivity and stereospecificity of the alpha,beta-dihydroxyacid dehydratase from Salmonella typhimurium.

1. In addition to the known 2R,3R- and 2R, 3S-2,3-dihydroxy-3-methylpentanoic acids (DHI), the 1S,3S- and sS,DR-isomers were prepared. 2S-2,3-Dihydroxy-3-methylbutanoic acid (DHV) was also prepared in addition to the known 2R-isomer. 2. The six dihydroxy acids were examined for their ability to promote the growth of isoleucine-valine (ilv)-requiring strains of Salmonella typhimurium and to serve as substrates for the alpha,beta-dihydroxyacid dehydratase of the same organism. 3. Only 2R,3R-2,3-dihydroxy-3-methylpentanoic and 2R-2,3-dihydroxy-3-methylbutanoic acids supported growth of the ilv strains of S. typhimurium. 4. alpha,beta-Dihydroxyacid dehydratase utilized the three isomers with the 2R-configuration as substrates but not those with the 2S-configuration. 5. In an additional growth study that utilized the 3R- and 3S-isomers of 3-methyl-2-oxopentanoic acid, the alpha-keto acid analogue of isoleucine, only the 3S-isomer supported growth. 6. It is concluded that the mechanism of action of the dehydratase is stereospecific in that the proton that is attached to C-3 of the substrate occupies the same steriochemical position as the departing hydroxyl group (Fig. 6).     

Benzofuranoid Neolignans from Piper kadsura

In a continuing research for neolignans from Piper kadsura (Choisy) Ohwi, six benzofuranoid neolignans were isolated from the aerial part of the plant. Their structure determination were based on the spectroscopic analysis (UV, IR, MS, NMR and CD) and derivative synthesis. Three of the isolated compounds were identified as new structures: 7R, 8R, 1′S-△8′-3, 4-methylenedioxy-5′-methoxy-l′, 4′-dihydro-4′-oxo-7, 0, 2′, 8. l′-neolignan ( Ⅰ ), 7 R, 8 R, 1 ′ R- △8′ - 3,4- methylenedioxy- 1 ′- methoxy - 1′,6′- dihydro- 6′- oxo- 7.0.4′,8. 3′-neolignan (Ⅳ) and 7R, 8R, 1′S-△8′-3, 4-methylenedioxy-l′-methoxy-1′,6′-dihydro-6′-oxo-7.0.4′,8.3′-neolignan (Ⅴ). Known compounds among them are 7R, 8S,1′S-△8′-3, 4-methylenedioxy-5′-methoxy-1′, 4′-dihydro-4′-oxo-7. 0. 2′, 8. 1′-neolignan(Ⅱ), 7S, 8S, 1′R-△8′-3, 4, 5′-trimethoxy-1′, 4′-dihydro-4′-oxo-7.0. 2′, 8. 1′-neolignan (Ⅲ) and 75, 85, 1′S-△8′-3, 4, l′-trimethoxy-l′, 6′-dihydro-6′-oxo-7. 0. 4′, 8. 3′-neolignans (Ⅵ). All of them were isolated from the plant for the first time.     

Assay of physiological levels of 2,3-butanediol diastereomers in blood and urine by gas chromatography-mass spectrometry

We present an assay for 2,3-butanediol by gas chromatography-mass spectrometry of its trimethylsilyl ethers. 2R,3R- and/or 2S,3S-2,3-butanediol and meso-2,3-butanediol are quantitated with corresponding internal standards of [2,3-2H2]butanediol. Limits of detection are 1 and 0.1 microM for split and splitless injections, respectively. Blood concentrations of 2,3-butanediol in nonalcoholics are 0.5 +/- 0.3 (SD) microM for 2R,3R- and/or 2S,3S-2,3-butanediol and 0.8 +/- 0.4 microM for meso-2,3-butanediol (n = 9). Two hours after alcohol ingestion, blood levels had risen in eight of nine subjects to 1.2 +/- 0.7 microM for 2R,3R-/2S,3S-2,3-butanediol and to 1.2 +/- 0.6 microM for meso-2,3-butanediol. Baseline urinary excretion of 2,3-butanediol is 0.4 +/- 0.2 mumol/mmol creatinine for 2R,3R-/2S,3S-2,3-butanediol and 0.9 +/- 0.5 mumol/mmol creatinine for meso-2,3-butanediol.     

Metabolism of 3-deoxy-3-fluoro-D-mannose and 4-deoxy-4-fluoro-D-mannose by Saccharomyces cerevisiae S288C.

Incubation of Saccharomyces cerevisiae S288C with 4-deoxy-4-fluoro-D-[1-14C]-mannose resulted in the formation of three metabolites that were characterized as 4-deoxy-4-fluoro-D-[1-14C]mannose 1,6-bisphosphate, 4-deoxy-4-fluoro-D-[1-14C]-mannose 6-phosphate and GDP-4-deoxy-4-fluoro-D-[1-14C]mannose. In addition, radioactive material was incorporated into a particulate fraction composed primarily of cell-wall polysaccharides. Compared with the 4-fluoro sugar, 3-deoxy-3-fluoro-D-[1-14C]mannose was not transported into yeast cells as well, and its conversion into sugar nucleotide was much less efficient. Metabolites that were isolated after incubation with the 3-fluoro analogue were identified as 3-deoxy-3-fluoro-D-[1-14C]mannose 1,6-bisphosphate, 3-deoxy-3-fluoro-D-[1-14C]mannose 6-phosphate and GDP-3-deoxy-3-fluoro-D-[1-14C]mannose. Little radioactivity was transferred into the cell-wall fraction.     

Synthesis and characterization of stereoisomers of 5,6-dihydro-5,6-dihydroxy-thymidine

Six products were isolated by reverse phase HPLC from the reaction of thymidine with osmium tetroxide. Four of the products were identified as stereoisomers of 5,6-dihydro-5,6-dihydroxy-thymidine (TG). The absolute configurations of these four compounds (from the shortest to the longest HPLC retention times) were determined by two-dimensional nuclear magnetic resonance spectroscopy to be (-)-trans-5S,6S-, (+)-trans-5R,6R-, (-)-cis-5R,6S-, and (+)-cis-5S,6R-5,6-dihydro-5,6-dihydroxy-thymidine. The other two products were dimers with unknown linking sites. Parameters of the mass and nuclear magnetic resonance spectra are reported and discussed.     

Metabolism of 2-deoxy-2-fluoro-D-[3H]glucose and 2-deoxy-2-fluoro-D-[3H]mannose in yeast and chick-embryo cells.

2-Deoxy-2-fluoro-D-[3H]glucose and 2-deoxy-2-fluoro-D-[3H]mannose have been prepared by tritiation of the corresponding unlabeled 2-fluoro sugars. The tritiated 2-fluoro sugars are phosphorylated and activated by UTP and by GTP to yield UDP-2-deoxy-2-fluoro-D-[3H]glucose, UDP-2-deoxy-2-fluoro-D-[3H]mannose, GDP-2-deoxy-2-fluoro-D-[3H]glucose and GDP-2-deoxy-2-fluoro-D-[3H]mannose in both cell types. The nucleotide derivatives could also be labeled in the nucleotide moiety by feeding the cells with [14C]uridine or [14C]guanosine in the presence of unlabeled 2-fluoro sugar. No evidence was obtained for metabolic steps in which the six-carbon chain of 2-fluoro sugars was not preserved. No epimerisation of the label to 2-deoxy-2-fluoro-D-[3H]galactose could be observed by radioactive gas-liquid chromatography of the enzymatic cleavage products of the different 2-fluoro sugar metabolites isolated from either cell type. Yeast and chick embryo cells both incorporate 2-deoxy-2-fluoro-D-[3H]glucose and 2-deoxy-2-fluoro-D-[3H]mannose specifically into glycoproteins, although this incorporation is very low when compared to the incorporation of 2-deoxy-D-[3H]glucose.     

Novel synthesis of cholesterol analogs: condensation of pregnenolone with dihydropyran or dihydrofuran.

Pregnenolone 3-(2'-tetrahydropyranyl) ether (1) was condensed with 3,4-[2H]dihydropyran to mainly give (20R)-[6'-(3',4'-[2'H]dihydropyranyl)]-pregn-5-ene-3 beta,20-diol 3-(2'-tetrahydropyranyl) ether (20R-3), according to nuclear magnetic resonance (NMR). Cold, dilute HCl in ethanol removed the tetrahydropyranyl group at C-3 and also opened the dihydropyranyl ring at the C-20 position of 20R-3 to give (20R)-27-norcholest-5-en-22-one-3 beta,20,26-triol (20R-5). Analogous results were obtained by condensing pregnenolone 3-acetate with 3,4-[2H]dihydropyran to provide (20R)-[6'-(3',4'-[2'H]dihydropyranyl)]-pregn-5-ene-3 beta,20-diol 3-acetate (20R-4). Acid-catalyzed opening of the dihydropyranyl ring at C-20 in 20R-4 yielded 20R-7, which, on acetylation followed by crystallization, provided (20R)-27-norcholest-5-en-22-one-3 beta,20,26-triol 3,26-diacetate (20R-8), identical to the diacetate made from 20R-5. Varying the reaction sequence beginning with 20(R,S)-4 gave an 84:16 ratio of 20R to 20S in a mixture of 20(R,S)-8, according to NMR analysis. Crystallization of the mixture from methanol provided pure 20R-8. Condensing 2,3-dihydrofuran and 1 for producing (20R)-[5'-(2',3'-dihydrofuranyl)]-pregn-5-ene-3 beta,20-diol 3-(2'-tetrahydropyranyl) ether (6) gave instead (20R)-26,27-bisnorcholest-5-en-22-one-3 beta,20,25-triol 3-(2'-tetrahydropyranyl) ether (20R-9) by partial hydrolysis during workup. Treating 20R-9 briefly with dilute HCl produced (20R)-26,27-bisnorcholest-5-en-22-one-3 beta,20,25-triol (20R-10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Convenient synthesis of 3- and 6-deoxy-D-myo-inositol phosphate analogues from (+)-epi- and (-)-vibo-quercitols

Starting from (+)-epi- and (-)-vibo-quercitols readily produced by bioconversion of myo-inositol, some biologically interesting phosphate and polyphosphate analogues, including the Ins(1,4,5)P(3) derivatives of 3-deoxy- and 6-deoxy-D-myo-inositol, could be readily prepared in a conventional manner. In addition, chemical modification at C-2 of the 3-deoxy Ins(1,4,5)P(3) provided 2-epimer, and 2-deoxy and 2-deoxy-2-fluoro forms. Eight polyphosphate analogues obtained were assayed for biological activity against PDH-Pase and PDH-K, and G6Pase, but none proved positive.     

Partial purification and some properties of oxalacetase from Aspergillus niger.

1. Oxalacetase from Asperigillus niger was found to be an inducible enzyme, the induction being dependent not only on neutralisation of the acidic growth medium but also on the presence of carbonate. An explanation is proposed. 2. Three methods were established for the quantitative determination of oxalacetase activity. These are based on the determination of the product acetate, on the absorbance of oxaloacetate and on coupling the hydrolysis of oxaloacetate to the oxidation of malate by NAD in the presence of malate dehydrogenase. 3. Oxalacetase was purified about 50-fold from cell-free extracts of A. niger and used to determine some of its properties such as kinetic constants. 4. 2S-[U-14C, 3-2H2] Malate in the presence of oxalacetase, NAD and malate dehydrogenase was partially converted to acetate and oxalate. The 3H/14C ratio of the isolated acetate was nearly twice as high as that of the malate used initially. The result demonstrates that the keto form of oxaloacetate, not the enol, is the substrate of the enzyme. 5. Equimolecular mixtures of 2S, 3S-[3-2H1] malate + 2S-[2-2H1] malate (mixture 1) and 2S, 3R-[3-2H1, 3H1] malate + 2S, 3R-[2-2H1, 3-3H1] malate (mixture 2) were prepared from 2S-[3-3H2] malate by incubation with fumarase in normal and tritiated water, respectively. The isolated mixture 1, in the presence of oxalacetase, NAD and malate dehydrogenase was incubated in tritiated water for formation of acetate and oxalate; the isolated mixture 2 was treated likewise in normal water. 6. The mixtures of symmetrically labelled [3H1] acetate and chiral acetates thus produced were isolated and the configuration of the [3H1, 3H1] acetate specimens was determined in the sequence acetate leads to malate leads to fumarate, as usual. The [2H1, 3H1] acetate derived from 2S, 3S-[3-2H1] malate (present in mixture 1( yielded a malate which on incubation with fumarase retained 65.0% of its total tritium content. This chiral acetate, therefore, had the R configuration. The [2H1, 3H1] acetate derived from 2S, 3R-[2-2H1, 3-3H1] malate produced a malate which retained 35% of its total tritium content, and therefore had the S configuration. 7. It was concluded that the detachment of the oxaloyl residue from oxaloacetate and its replacement by a proton proceed with inversion of configuration at the methylene group which becomes methyl during the hydrolysis.     

Synthesis and receptor binding of oxytocin analogs containing conformationally restricted amino acids

Summary We report the solid-phase synthesis and receptor-binding properties of eleven oxytocin analogs (Mpa-Xxx-Ile-Gln-Asn-Cys-Sar-Arg-Gly-NH₂) containing non-coded amino acids in position 2: D-α- and L-α-(2-indanyl)glycine, R,S-6-methoxy-2-aminotetralin-2-carboxylic acid, D- and L-pentafluorophenylalanine, D,L-2,4-dimethylphenylalanine, D,L-2,4,6-trimethylphenylalanine, R,R- and S,S-1,2,3,4-tetrahydro-1-methyl-β-carboline-3-carboxylic acid and R- and S-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid. Some of these amino acid analogs (2-indanylglycine and D-pentafluorophenylalanine) were earlier successfully applied for the synthesis of potent bradykinin antagonists [1, 2]. Their receptor bindings were tested on isolated guinea-pig uterus, rat liver and rat kidney inner medulla plasma membranes. The extent of binding of the peptides to the oxytocin receptor was in several cases was even higher than that of the parent hormone (oxytocin). However, the real pharmacological value of these analogs can be evaluated only afterin vivo measurements of their inhibition of uterine motor activity.     

Enzymic generation of chiral acetates. A quantitative evaluation of their configurational assay.

1. R-Acetate was generated enzymically from R-acetate in the sequence acetate leads to malate leads to oxaloacetate leads to acetate, and S-acetate likewise from S-acetate. It was concluded that the formation of malate on malate synthase involves the operation of a normal isotopic effect combined with inversion of configuration. The malate synthase kH/k2H was determined as 3.7 +/- 0.5 by a method which yields results independently of the stereochemical purity of the chiral acetates used initially. 2. R-Acetate was also generated from R-acetate in the sequence acetate leads to citrate leads to malate leads to oxaloacetate leads to acetate, and S-acetate likewise from S-acetate. The conclusion is the same as given above, but refers to the formation of citrate on the re-synthase. 3. 2S,3R-[2-2H1,3-2H1,3H1]Malate and 2S,3S-[2-2H1,3-2H1]malate were prepared from 2S-[2,3-2H3]malate by treatment with fumarase in tritiated water and normal water, respectively. It was assumed that these malate specimens were pure with respect to chirality as generated by isotopic labelling. 4. These two malate specimens were partially converted (about 9%) to acetates in conditions where no racemization at the level of transiently formed oxaloacetate occurred. That no racemization took place was demonstrated experimentally. Oxidative enzymic hydrolysis of 2S,3R-[2-2H1,3-2H1,3H1]malate in normal water and of 2S,3S-[2-2H1,3-2H1]malate in tritiated water produced S-[2H1,3H1]acetate and R-[2H1,3H1]acetate, respectively. 5. The isolated R-[2H1,3H1]acetate and S-[2H1,3H1]acetate on configurational analysis yielded malates which in the presence of fumarase retained 79.7 +/- 0.7% and 20.3 +/- 0.9%, respectively, of their total tritium content. The symmetric deviation from the 50% value found with [3H1]acetate strengthens the conclusion that stereochemically pure chiral acetates were analyzed. The malate synthase kH/k2H was determined from the data of this study as 3.9 +/- 0.2. 6. The average of the values given under paragraphs 1 and 5 for the isotopic discrimination on malate synthase corresponds to kH/k2H=3.8 +/- 0.1. It was concluded that the configurational analysis of stereochemically pure R-[2H1,3H1]acetate and S-[2H1,3H1]acetate yields malates which in the presence of fumarase retain 79 +/- 2% and 21 +/- 2%, respectively, of their total tritium content. Hence, a deviation of 29 +/- 2% from the 50% value represents the actual amplitude of the configurational assay. 7. Outlines are given for an enzymic generation of chiral acetates in preparative scale.     

Fluorinated carbohydrates as potential plasma membrane modifiers. Synthesis of 4- and 6-fluoro derivatives of 2-acetamido-2-deoxy-D-hexopyranoses

2-Amino-2,4-dideoxy-4-fluoro- and 2-amino-2,4,6-trideoxy-4, 6-difluoro-D-galactose, and 2-amino-2,4-dideoxy-4-fluoro- and 2-amino-4-deoxy-4, 4-difluoro-D-xylo-hexose were synthesized, as potential modifiers of tumor cell-surface glyco-conjugate, from benzyl 2-acetamido-3-O-benzyl-2-deoxy-4, 6-di-O-mesyl-alpha-D-glucopyranoside and benzyl 2-acetamido-3, 6-di-O-benzyl-2-deoxy-4-O-mesyl-alpha-D-glucopyranoside, which were converted into the corresponding 4,6-difluoro-2,4, 6-trideoxy and 2,4-dideoxy-4-fluoro derivatives. Benzyl 2-acetamido-2-deoxy-4-O-mesyl-alpha-D-galactopyranoside and benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-alpha-D-xylo-hexo-4-ulopyra noside were treated with diethylaminosulfur trifluoride to give 2-amino-2,4-dideoxy-4-fluoro-D-glucose and 2-amino-2,4-dideoxy-4, 4-di-fluoro-D-xylo-hexose derivatives, respectively, to give after deprotection the target compounds. Several of the peracetylated sugar derivatives inhibited L1210 tumor-cell growth in vitro at concentrations of 1-5 10(-5) M. The peracetylated derivative of 2-amino-2,4-dideoxy-4-fluoro-D-galactose inhibited protein and glycoconjugate biosynthesis, and also exhibited antitumor activity in mice with L1210 leukemia.     

Enthalpy change on mixing a couple of S- and R-enantiomers of some chiral compounds at 298.15 K

Enthalpy change on the mixing of R- and S-enantiomers of chiral liquid compounds such as dimethyl malate (1), methyl 3-hydroxylbutanoate (2), 2-butanol (3), ethyl 4-chloro-3-hydroxylbutanoate (4), 1,3,3-trimethylbicycle-[2.2.1]heptan-2-one (5), 3,7-dimethyl-6-octenal (6), and 8-bromo-2,6-dimethyl-2-octene (7) is measured over the entire range of mole fractions at 298.15 K, albeit very small values. The mixing of chiral liquids of R-1 + S-1, R-2 + S-2, R-3 + S-3, R-6 + S-6, and R-7 + S-7 produces enthalpic destabilization over the entire range of mole fractions, while that of R-4 + S-4 and R-5 + S-5 shows enthalpic stabilization over entire compositions. Enthalpy change on mixing at an equimolar concentration and the intermolecular interaction obtained by the molecular mechanics calculations show a linear correlation, except for a few compounds measured.     

Cyclopenta[g]quinazoline-based antifolates: the effect of the chirality at the 6-position on the inhibition of thymidylate synthase (TS).

Cyclopenta[g]quinazoline-based inhibitors of thymidylate synthase (TS) possess a chiral centre at the 6-position of the molecule. The effect of this chirality on the inhibition of TS was investigated by synthesising compounds 6S-1a-c, 6R-1a-c. It was shown, in particular with the diastereoisomers 6S-1c, 6R-1c, that the inhibitory activity against TS is mainly due to the 6S diastereoisomer rather than the 6R diastereoisomer, which is virtually inactive.     

Exploring relationships between mimic configuration, peptide conformation and biological activity in indolizidin-2-one amino acid analogs of gramicidin S.

Indolizidin-2-one amino acids (I2aas, 6S- and 6R-1) possessing 6S- and 6R-ring-fusion stereochemistry were introduced into the antimicrobial peptide gramicidin S (GS) to explore the relationships between configuration, peptide conformation and biological activity. Solution-phase and solid-phase techniques were used to synthesize three analogs with I2aa residues in place of the d-Phe-Pro residues at the turn regions of GS: [(6S)-I2aa4-5,4'-5']GS (2), [Lys2,2',(6S)-I2aa4-5,4'-5']GS (3) and [(6R)-I2aa4-5,4'-5']GS (4). Although conformational analysis of [I2aa4-5,4'-5']GS analogs 2-4 indicated that both ring-fusion stereoisomers of I2aa gave peptides with CD and NMR spectral data characteristic of GS, the (6S)-I2aa analogs 2 and 3 exhibited more intense CD curve shapes, as well as greater numbers of nonsequential NOE between opposing Val and Leu residues, relative to the (6R)-I2aa analog 4, suggesting a greater propensity for the (6S)-diastereomer to adopt the beta-turn/antiparallel beta-pleated sheet conformation. In measurements of antibacterial and antifungal activity, the (6S)-I2aa analog 2 exhibited significantly better potency than the (6R)-I2aa diastereomer 4. Relative to GS, [(6S)-I2aa4-5,4'-5']GS (2) exhibited usually 1/2 to 1/4 antimicrobial activity as well as 1/4 hemolytic activity. In certain cases, antimicrobial and hemolytic activities of GS were shown to be dissociated through modification at the peptide turn regions with the (6S)-I2aa diastereomer. The synthesis and evaluation of GS analogs 2-4 has furnished new insight into the importance of ring-fusion stereochemistry for turn mimicry by indolizidin-2-one amino acids as well as novel antimicrobial peptides.     

Synthesis of some monodeoxyfluorinated methyl and 4-nitrophenyl alpha-D-mannobiosides and a related 4-nitrophenyl alpha-D-mannotrioside

Treatment of methyl 3,4,6-tri-O-benzyl-2-O-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-alpha -D- mannopyranoside with N,N-diethylaminosulfur trifluoride (Et2NSF3), followed by O-deacetylation and catalytic hydrogenolysis, afforded methyl 2-O-(6-deoxy-6-fluoro-alpha-D-mannopyranosyl)-alpha-D-mannopyranoside (8). Methyl 6-deoxy-6-fluoro-2-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside (11) was similarly obtained from methyl 3-O-benzyl-2-O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl-alpha-D- mannopyranoside. 1,2,3,4-Tetra-O-acetyl-6-deoxy-6-fluoro-beta-D-mannopyranose (13), used for the synthesis of the 4-nitrophenyl analogs of 8 and 11, as well as their 3-O-linked isomers, was obtained by treatment of 1,2,3,4-tetra-O-acetyl-beta-D-mannopyranose with Et2NSF3. Treatment of 13 with 4-nitrophenol in the presence of tin(IV) chloride, followed by sequential O-deacetylation, isopropylidenation, acetylation, and cleavage of the acetal group, afforded 4-nitrophenyl 4-O-acetyl-6-deoxy-6-fluoro-alpha-D-mannopyranoside (18). Treatment of 13 with HBr in glacial acetic acid furnished the 6-deoxy-6-fluoro bromide 19. Glycosylation of diol 18 with 20 gave 4-nitrophenyl 4-O-acetyl-6-deoxy-6-fluoro-3-O- (21) and -2-O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)-alpha-D- mannopyranoside (23) in the ratio of approximately 2:1, together with a small proportion of a branched trisaccharide. 4-Nitrophenyl 4,6-di-O-acetyl-alpha-D-mannopyranoside was similarly glycosylated with bromide 19 to give 4-nitrophenyl 4,6-di-O-acetyl-3-O- and -2-O-(2,3,4-tri- O-acetyl-6-deoxy-6-fluoro-alpha-D-mannopyranosyl)-alpha-D-mannopyranosid e. The various di- and tri-saccharides were O-deacetylated by Zemplén transesterification.     

Fenugreekine,a new steroidal sapogenin-peptide ester of Trigonella foenum-graecum

A new C₂₇-steroidal sapogenin-peptide ester, fenugreekine, has been isolated from seeds of Trigonella foenum-graecum. On acid hydrolysis, it afforded diosgenin, yamogenin, (25R)-spirosta-3,5-diene, a mixture of three isomeric (2S,3R,4R-, 2S,3R,4S-, 2S,3S,4R-)-4-hydroxyisoleucine lactones, 4′-hydroxyisoleucyl-4-hydroxyisoleucine lactone, and a C₁₄-dipeptide which was partially characterized. On the basis of this chemical transformation and spectral (UV, IR, PMR, MS) evidence of fenugreekine and its transformation products, the steroidal sapogenin-peptide ester is assigned structure (1). The two dipeptides also have not been encountered before in nature or prepared synthetically. The compound shows a number of interesting pharmacological and virological activities.     

General methods for modification of sialic acid at C-9. Synthesis of N-acetyl-9-deoxy-9-fluoroneuraminic acid

Methyl 5-acetamido-3,5-dideoxy-2-O-methyl-D-glycero-D-galacto-2-nonulopyrano sate was converted into the 9-O-trityl derivative and the remaining hydroxyl groups were protected as benzyl ethers. Removal of the trityl group, followed by treatment with diethylaminosulfur trifluoride gave the 9-deoxy-9-fluoro derivative, and deprotection N-acetyl-9-deoxy-9-fluoroneuraminic acid (8). In another procedure, coupling of 2-acetamido-2,6-dideoxy-6-fluoro-D-glucopyranose with potassium di(tert-butyl) oxaloacetate, followed by hydrolysis and decarboxylation gave 8. Some of the derivatives were active as inhibitors of growth of mouse mammary adenocarcinoma (TA3) and L1210 cells in culture.     

A novel enantioselective synthesis of (S)-(-)- and (R)-(+)-nornicotine via alkylation of a chiral 2-hydroxy-3-pinanone ketimine template

An asymmetric synthesis of the optically pure isomers of the minor tobacco alkaloid and CNS nicotine metabolite, nornicotine, has been achieved with moderately high optical purity. The synthetic pathway involves alkylation of a chiral ketimine, prepared from either 1R,2R,5R-(+)- or 1S,2S,5S-(-)-2-hydroxy-3-pinanone and 3-(aminomethyl)pyridine with 3-bromopropan-1-ol. After cleavage of the respective C-alkylated ketimines with NH2OH.HCl, and treatment of the resulting amino alcohols with HBr, followed by base-catalyzed intramolecular ring closure, (S)-(-)-nornicotine and (R)-(+)-nornicotine were obtained with ee values of 91% and 81%, respectively.