Juan A. Galbis Pérez

Preparation of C-nucleosides by dehydration of pentahydroxypentyl-heterocycles: Steric course and mechanism

Abstract The acid-catalysed dehydration of pentahydroxypentyl-heterocycles can take place between C-1′ and C-4′ to yield C -nucleosides having furanoid structures, or between C-1′ and C-5′ to yield pyranoid compounds. Each reaction can yield one of the two possible anomers or a mixture of both. We have dehydrated pentahydroxypentyl-heterocycles having d - gluco , d - manno , and d - galacto configurations. When the reactions were kinetically controlled, the 6,6-dimethyl-2-(pentitol-1-yl)-4,5,6,7-tetrahydroindol-4-ones having the d - gluco or d - manno configurations yielded 2-α- d -arabinofuranosyl-6,6-dimethyl-4,5,6,7-tetrahydroindol-4-one, but they yielded 2-α- d -arabinopyranosyl-6,6-dimethyl-4,5,6,7-tetrahydroindol-4-one under conditions of thermodynamic control. Dehydration of 3-acetyl-2-methyl-5-( d - galacto -pentitol-1-yl)-1-propylpyrrole gave a mixture of 3-acetyl-5-(α- and β- d -lyxopyranosyl)-2-methyl-1-propylpyrrole. These results are consistent with a mechanism involving an intermediate C-1′ carbocation.

1-Aryl(glycofurano)imidazolidine-2-thiones derived from new 2-(alkylamino)-2-deoxyheptoses having d-glycero- d-galacto and d-glycero-d-talo configurations

Abstract The aminonitrile synthesis applied to d -mannose gave, in good yield, a mixture of the two epimeric heptosamines 2-deoxy-2-(ethylamino)- d -glycero-α- d -galacto-heptopyranose and 2-deoxy-2-(ethylamino)- d -glycero-β- d -talo-heptopyranose that could be fractionated by recrystallization. The stereochemistry at C-2 of both amino sugars, and of their acyl derivatives, was established from their 1H-n.m.r. spectra. This stereochemistry was also demonstrated by the preparation of the 3-alkyl-1-aryl(glycofurano)imidazolidine-2-thiones, whose structures were assigned from the 1H-n.m.r. spectra of their tetra-O-acetyl-derivatives. In a similar way, hemihydrogenation of the epimeric mixture of 2-deoxy-2-(propylamino)-heptononitriles gave an amorphous mixture of 2-deoxy-2-(propylamino)heptoses having the d -glycero- d -galacto and d -glycero- d -talo configurations. By reaction of this mixture with phenyl isothiocyanate, 1-phenyl-3-propyl-(1,2-dideoxy- d -glycero-β- d -talo-heptofurano)[2,1-d]imidazolidine-2-thione (21) was obtained. The structure of 21 was also demonstrated from the 1H-n.m.r. spectrum of its acetyl derivative.

Synthesis of d-ribo-C-nucleoside analogues by dehydration of new d-allo-pentitol-1-yl heterocycles

Abstract The reaction of 2-amino-2-deoxy- d - glycero - d - altro -heptose hydrochloride with acyclic and cyclic 1,3-dicarbonyl compounds gives, respectively, ( d - allo -pentitol-1-yl)-pyrroles and -tetrahydroindoles that can be dehydrated to yield d - ribo - C -glycosyl heterocycles having furanoid or pyranoid structures, depending on the reaction conditions. Thus, when the reactions were kinetically controlled, α- and β- d -ribofuranosyl heterocycles were obtained, but α- and β- d -ribopyranosyl heterocycles were formed under conditions of thermodynamic control. A criterion is proposed to differentiate between both structures on the basis of the mass spectra of their triacetates.

Preparation of new C-nucleosides by intramolecular dehydration of 2-pentahydroxypentyl-4,5,6,7-tetrahydroindol-4-ones

Abstract Acid-catalysed dehydration of the polyhydroxyalkyl chain of 6,6-dimethyl-2-( d - gluco -pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one and of 6,6-dimethyl-2-( d - manno -pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one gave 2-α- d -arabinofuranosyl-6,6-dimethyl-4,5,6,7-tetrahydroindol-4-one ( 3 ). In a similar way, 2-β- d -lyxopyranosyl-6,6-dimethyl-4,5,6,7-tetrahydroindol-4-one ( 8 ) and 2-β- d -lyxopyranosyl-4,5,6,7-tetrahydroindol-4-one ( 9 ) were obtained by dehydration of 6,6-dimethyl-2-( d - galacto -pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one and 2-( d - galacto -pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one, respectively. The structures of the new C -nucleosides described ( 3 , 8 , and 9 ) were elucidated by chemical and physical methods.

Reaction of 2-amino-2-deoxyheptoses with cyclic β-dicarbonyl compounds☆

Abstract The reaction between 2-amino-2-deoxyaldoses and β-dicarbonyl compounds yields polyhydroxyalkylpyrroles. Thus, 6,6-dimethyl-2-( D - galacto -pentitol-1-yl)-4,5,6,7-tetrahydroindol-4-one ( 4a ), 6,6-dimethyl-2-( D - gluco -pentitol-1-yl)-4,5,6,7-tetrahydroindol-4-one ( 4b ), and 6,6-dimethyl-2-( D - manno -pentitol-1-yl)-4,5,6,7-tetrahydroindol-4-one ( 4c ) have been obtained from 5,5-dimethylcyclohexane-1,3-dione ( 2 ) and 2-amino-2-deoxyheptoses having D - glycero - L - gluco ( 1a ), D - glycero - D - ido ( 1b ), and D - glycero - D - talo ( 1c ) configurations, respectively. 2-Amino-2-deoxy- D - glycero - L - manno -heptose ( 1d ), the epimer of 1a , also reacts with 2 , to yield 4a . In a similar way, 1a , 1b , and 1c react with cyclohexane-1,3-dione ( 3 ), to give 2-( D - galacto -pentitol-1-yl)-4,5,6,7-tetrahydroindol-4-one ( 5a ), 2- D - gluco -pentitol-1-yl)-4,5,6,7-tetrahydroindol-4-one ( 5b ), and 2-( D - manno -pentitol-1-yl)-4,5,6,7-tetrahydroindol-4-one ( 5c ), respectively.

Preparation of 1-aryl-2-(benzylthio)-(1,2-dideoxy-D-glycero-β-L-gluco-heptofurano)[1,2-d]-2-imidazolines, and new, acyclic C-nucleosides of the imidazole

Abstract The reaction of 1-aryl-(1,2-dideoxy- d - glycero -β- l - gluco -heptofurano)[1,2- d ]imidazolidine-2-thiones with benzyl chloride and an equivalent amount of sodium hydrogencarbonate yields 1-aryl-2-(benzylthio)-(1,2-dideoxy- d - glycero -β- l - gluco -heptofurano)[1,2- d ]-2-imidazolines ( 2 ). If the reaction is carried out in the absence of sodium hydrogencarbonate, the 1-aryl-2-(benzylthio)-4-( d - galacto -pentitol-1-yl)imidazoles are obtained. These compounds are also obtained by acid-catalyzed isomerization of compounds 2 .

Synthesis of 1-aryl-(glycofurano)imidazolidine-2-thiones from new 2-(alkylamino)-2-deoxyhexoses

Abstract The new amino sugars 2-deoxy-2-(ethylamino)-α- l -glucopyranose, 2-deoxy-2-(propylamino)-α- l -glucopyranose, and 2-deoxy-2-(ethylamino)-α(or β)- l -mannopyranose have been prepared from l -arabinose by the aminonitrile synthesis. The reaction between these aminohexoses and aryl isothiocyanates affords the corresponding 3-alkyl-1-aryl-(1,2-dideoxy-α- l -glucofurano)[2,1- d ]imidazolidine-2-thiones and 3-alkyl-1-aryl-(1,2-dideoxy-β- l -mannofurano)[2,1- d ]imidazolidine-2-thiones. The structures of the new compounds described were elucidated by chemical and physical methods.

Limitations of the aminonitrile synthesis. New products from d-glucose, d-galactose, and d-mannose

Abstract The reaction of aldoses with an excess of amine and hydrogen cyanide can yield a series of cyclic and acyclic compounds in addition to the expected α-aminoaldononitriles. The nature of these unexpected products depends on the specific reaction conditions and on the structure of the aldose. Thus, the α-aminoheptononitriles formed from d -glucose, d -galactose, and d -mannose can be transformed into 2-alkylamino-1,4-anhydro-2-deoxy-1-imino(or alkylimino)heptitols ( 1–6 ), N 1 -alkyl-2-alkylamino-2-deoxyheptonamidines ( 10a and 10c ), or N -alkyl-2-alkyl-amino-2-deoxyheptonamides ( 11a–11c , 12c , and 13a–13c ), depending on the reaction conditions.

Accuracy and effectiveness of low cost UASs and open source photogrammetric software for foredunes mapping

ABSTRACT The recent use and availability of small and low cost Unmanned Aerial Systems (UAS) and the development of Open Source Photogrammetric (OSP) software opens new opportunities for their intensive use in topographic monitoring of foredune dynamics. This study assesses the accuracy and effectiveness of high resolution Digital Surface Models (DSM) generated by the combined use of low-altitude UAS imagery and OSP software. The Photogrammetric Workflow (PW) has been optimized to address the use an action camera and non-autonomous flight mode. To evaluate the accuracy of the DSMs derived from dense matching of UAS imagery we use a reference DSM obtained by a Terrestrial Laser Scanner in the same survey period. Moreover, we use robust statistical indicators for assessing the vertical accuracy of both DSMs: the raw DSM and the denoised DSM. The results shows that a detailed UAS-based DSM with a spatial resolution of 5 cm and vertical accuracy of 10 cm (robust root mean square error) can be obtained by using the proposed PW. The results also suggest that this low cost technology can be used effectively for 3D mapping of foredunes.

On the positional accuracy and maximum allowable scale of UAV-derived photogrammetric products for archaeological site documentation

Abstract Blending photogrammetric and Structure from Motion techniques with Unmanned Aerial Vehicles (UAV) is a commonly used approach for the documentation and analysis of archaeological sites. Using the dense 3D point clouds generated from these techniques, two main photogrammetric products are created: orthophotos and Digital Surfaces Models (DSM). Depending on the UAV technology, the flight parameters, the topography and land cover of the flown area, DSMs and orthophotos are delivered with varying positional accuracies and output scales. In this paper, the positional accuracy and maximum allowable scale of these products generated by complete automation of flight mode and processing workflow are assessed. Moreover, three known International Mapping Standards (IMS) are validated using independent checkpoints, obtained by geodetic Global Navigation Satellite Systems receivers, in two Spanish study areas. The results show that accurate photogrammetric products adapted to the IMS can be successfully obtained by the automation of the photogrammetric workflow.