Phase transitions in 1,2- and 1,3-diacyl-sn-glycero-3-phosphocholine monolayers at the oil/water interface.

Moving the phosphatidylcholine group from the 3- to the 2-position in monolayers of distearoyl-sn-glycero-3-phosphocholine at the oil/water interface expands the surface pressure-area isotherm and markedly increases the surface pressure at which phase separation occurs with only a slight change in the monolayer surface density at the onset of the transition. This is interpreted in terms of a change in an ordering parameter in the solid-condensed state.     

O-Benzylated thio sugars. Derivatives of 2,3,6-tri-O-benzyl-1-thio-d-galactopyranose suitable for use in oligosaccharide synthesis

The 4-O-benzoyl (15a) 4-O-p-nitrobenzoyl (15b) derivatives of 2,3, 6-tri-O-benzyl-1-thio-d-galactopyranose were synthesized from allyl 2,6-di-O-benzyl-α-d-galactopyranoside (1). In the first stage of the synthesis the 3-position of 1 was benzylated by an indirect route, and also by the direct reaction (preferred) of benzyl bromide with the 3,4-O-dibutylstannylene intermediate 7. The product 6 was sequentially isomerized (allyl → 1-propenyl), acylated at the 4-position, and hydrolyzed. The free sultars 11a and 11b were converted into the thio sugars by a standard sequence involving formation of the glycosyl halides 13a and 13b and the reaction of these with appropriate sulfur nucleophiles. A third derivative (29) of 2,3,6-tri-O-benzyl-1-thio-d-galactopyranose, having a 4-O-allyl protecting group, was similarly made from the corresponding normal sugar 25. The key intermediate 22, precursor to 25, was prepared by two routes from methyl 2,3,6-tri-O-benzoyl-α-d-galactopyranoside (17).     

O-Benzylated thioglucoses, intermediates for the synthesis of (1→6)- and (1→4)-linked oligosaccharides: S-benzylation, coupling, and thioglycoside cleavage

The use of the chloroacetyl group as a protecting group has been studied for a 2-methylglyco-[2′,1′:4,5]-2-oxazoline. The reaction of chloroacetyl chloride or chloroacetic anhydride with 2-acetamido-1,3,4-tri-O-acetyl-2-deoxy-β-d-glucopyra-nose provided 2-acetamido-1,3,4-tri-O-acetyl-6-O-(chloroacetyl)-2-deoxy-β-d-glucopyranose which, on treatment with anhydrous ferric chloride in dichloromethane, produced the desired oxazoline. The glycosylating capability of the oxazoline has been investigated with aglycon hydroxides, to give the corresponding 2-acetamido-2-deoxy-β-d-glucopyranosides. The chloroacetyl group can be selectively removed by treatment with thiourea, and migration of O-acetyl groups was not observed under these conditions.     

3-desoxyhex-2-enono-1,4-lactone aus D-hexofuran(osid)- urono-6,3-lactonen

The yield of 2-O-benzyl-3-deoxy-L-threo-hex-2-enono-1,4-lactone by reaction of 5-O-benzyl-1,2-O-isopropylidene-α-D-glucofuranurono-6,3-lactone with sodium borohydride was improved by variation of the aprotic dipolar solvent and temperature. The general validity of this elimination—reduction reaction was ascertained by conversion of eleven other D-hexofuran(osid)urono-6,3-lactones into various 3-deoxy-hex-2-enono-1,4-lactones by treatment with sodium borohydride in hexamethyl phosphoric triamide.     

Oligosaccharide synthesis by the thioglycoside scheme on soluble and insoluble polystyrene supports

The solid-phase synthesis of a disaccharide via the thioglycoside approach is described. Treatment of (chloromethyl)polystyrene, either cross-linked (1-X) or linear (1-L), with the 1-thio sugar 4 gave resins (6-X, 6-L) carrying thioglycosidically bound 2,3,4-tri-O-benzyl-D-glucopyranosyl groups. Alternatively, the conversion of 1-X into (mercaptomethyl)polystyrene (3-X) and reaction of this with the glucosyl chloride 5 gave 6-X. By repeated treatments with 6-O-acetyl-2,3,4-tri-O-benzyl-α-D-glucopyranosyl bromide, a second D-glucose residue was coupled to 74–92% of the first sugar residues. The action of methyl iodide—benzyl alcohol in refluxing benzene quantitatively cleaved the sugars from the polystyrene support, forming benzyl glycosides (13, 7) and, from the unreacted monosaccharide residues, the 1,6-anhydro sugar 9. The coupling product was 92–95% α-linked. Deprotection and purification gave isomaltose.     

Synthetic studies on amino-alpha-glycosides of aminocyclitols. Synthesis of kanamycin analogues

A diastereoisomer of Kanamycin C has been synthesized by a modified Koenigs—Knorr reaction of 3,4,6-tri-O-acetyl-2-(2,4-dinitroanilino)-2-deoxy-α-D-glucopyranosyl bromide with 4-O-(3-acetamido-2,4,6-tri-O-benzyl-3-deoxy-α-D-glucopyranosyl)-N,N′-di[(benzyloxy)carbonyl]-2-deoxystreptamine. Several Kanamycin analogues were synthesized by a similar condensation reaction. Each of the condensed products was isolated as its crystalline tetra-N-acetyl derivative and was proved by n.m.r. spectroscopy in D₂O to have the α-configuration.     

O-benzylated thio sugars: 2,3,4- and 2,4,6-tri-O-benzyl-1-thio-β-d-galactopyranose

The 2,3,4- (9) and 2,4,6-tribenzyl (19) ethers of 1-thio-β-d-galactopyranose were prepared from the corresponding O-benzylated normal (1-hydroxyl) sugars 4 and 15 via the sequence: normal sugar → diacetate → O-acetylglycosyl bromide → O-acetyl-glycosyl ethylxanthate → 1-thio sugar. 2,3,4-Tri-O-benzyl-α-d-galactopyranose (4) is most advantageously made from allyl 6-O-allyl-α-d-galactopyranoside (2) by a published synthesis. An improved synthesis of 2,4,6-tri-O-benzyl-d-galactopyranose (15) was devised; it involves the selective 3-O-benzoylation of allyl 2,6-di-O-benzyl-α-d-galactopyranoside (10).     

Aminoglycosides of D-pinitol. The 3-amino-3-deoxy-α-D-glucopyranoside,THE 3-acetamidino analog,and the 3,6-dideoxy-3,6-epimino-α-D-glucopyranoside

3-Azido-2,4,6-tri-O-benzyl-3-deoxy-α-D-glucopyranosyl chloride (7), prepared conventionally from the azido precursor 2, was coupled with “diisopropylidene-D-pinitol” (8) to give the α-D-glucoside 9 in good yield, together with some β anomer. Removal of the O-benzyl groups from 9 and reduction of the azido group to ?NH₂ were accomplished simultaneously. Further deprotection yielded 11, a 3-amino-3-deoxy-α-D-glucoside of D-pinitol (1a). Compound 11 was converted into the (impure) 3-acetamidino hydrochloride 12. The synthesis of 3,6-epimino-D-glucosides was accomplished by ring closure of the 3-N-tosyl-6-O-tosyl intermediates 17 and 13. The products, after deprotection, were methyl 3,6-dideoxy-3,6-epimino-β-D-glucopyranaside (20) and the novel 3,6-epimino analog 15 of the pinitol D-glucoside 11.     

Further immunochemical studies on the combining sites of Lotus tetragonolobus and Ulex europaeus I and II lectins

A series of 2-O-benzoyl-4,6-di-O-benzyl-α-d-galactopyranosyl halides carrying either a second benzoyl group (8a, 12a) or a selectively removable, temporary protecting group (8b–d, 12b) at position 3 was synthesized from allyl α-d-galactopyranoside (1). The key intermediate was 1-propenyl 4,6-di-O-benzyl-α-d-galactopyranoside (5), prepared from 1 via the 4,6-O-benzylidene-2,3-di-O-crotyl derivative 2. The successive incorporation of the 2-O-benzoyl group, by selective acylation at low temperature, and of various 3-substituents gave fully substituted 1-propenyl α-d-galactopyranosides 6a–d. These were converted into the glycosyl halides by published methods. An improved preparation of allyl 2,6-di-O-benzyl-(15) and 2,4,6-tri-O-benzyl-(19) α-d-galactopyranoside was achieved. The direct acetonation of 1 to the 3,4-O-isopropylidene derivative 13, followed by benzylation and mild acid hydrolysis, gave 15 in 56% yield. The transient protection of O-3 in 15 was accomplished by the alkylation of the dibutylstannylene derivative 16 with (2-methoxyethoxy)methyl chloride. Successive benzylation and mild acid hydrolysis of the product 17 efficiently furnished 19.     

Analysis of radioactive and nonradioactive purine bases,nucleosides, and nucleotides by high-speed chromatography on a single column

The concentrations of radioactive and nonradioactive purine bases, purine nucleosides, purine mono-, di-, and trinucleotides in acid extracts of fibroblasts were determined by anion-exchange column chromatography. The concentrations of nonradioactive components were determined by computerized integration of the signal from a double-beam uv-detector. The radioactive metabolites were quantitated by high-efficiency, continuous liquid scintillation counting, employing a discrete sample transport system.     

Genetical and biochemical evidence that a novel dinucleoside polyphosphate coordinates salvage and de novo nucleotide biosynthetic pathways in mammalian cells

Studies with ‘wild type’ Chinese hamster ovary cells and mutant derivatives defective in purine salvage and $\text{de novo}$ nucleotide biosynthesis pathways have brought to light the possibility that an unusual dinucleoside polyphosphate, HS-3 (see appendix) is a crucial regulator of these two pathways. Three antitumor drugs, methotrexate, 5-fluorouracil and azaserine as well as L-glutamine, purines and pyrimidines were used to define the loci of HS-3 metabolism. Wild type and salvage pathways mutants accumulated HS-3 in the absence of glutamine. $\text{De novo}$ pathways mutant accumulated HS-3 only when purine was absent. Depletion of HS-3 was induced in wild type and $\text{de novo}$ mutant cell lines by purine compounds. Salvage pathways mutants did not cause depletion of HS-3 when supplied with purines or pyrimidines, except 5-fluorouracil. Data indicate that HS-3 is probably synthesised when an early step in purine nucleotide synthesis is blocked and depleted when the salvage pathways are operative. HS-3 may be an important factor in certain diseases involving nucleotide metabolism.     

Underestimation of cyclic 3',5'-nucleotide phosphodiesterase activity by a radioisotopic assay using an anionic-exchange resin.

The anionic-exchange resin technique utilizing isotopically labeled cyclic AMP (or cyclic GMP) and an auxiliary enzyme, 5′-nucleotidase, for the assay of phosphodiesterase (Thompson, M. J., and Appleman, M. M. (1971) Biochemistry10, 311) does not accurately measure the enzyme activity due to adsorption of the product (adenosine or guanosine) by the resin. Binding of adenosine or guanosine by the resin may lead to an underestimation of phosphodiesterase activity. Under comparable conditions, adsorption of guanosine by the resin is much larger than that of adenosine. Consequently, cyclic GMP phosphodiesterase activity is underestimated more than cyclic AMP phosphodiesterase activity.