Synthesis of mucin-type O-glycan probes as aminopropyl glycosides

• David Benito-Alifonso,
• Rachel A. Jones,
• Anh-Tuan Tran,
• Hannah Woodward,
• Nichola Smith and
• M. Carmen Galan

Beilstein J. Org. Chem. 2013, 9, 1867–1872, doi:10.3762/bjoc.9.218

• %) to yield final targets 2 and 3 in 60% and 70% yield, respectively (Scheme 1). Access to branched core 2 trisaccharide 4 was accomplished by 4,6-O-benzylidene acetal cleavage from disaccharide 15 using a modified procedure from Chang et al. [21] whereby reaction with p-TsOH in MeOH under sonication

• peracetylated trichloroacetimidate donor 13 in the presence of catalytic TMSOTf. Disaccharide 24 was obtained in 62% yield and without any further protecting-group manipulations, the thioglycoside disaccharide was subsequently activated as a glycosyl donor using NIS/TMSOTf and coupled to 4,6-O-benzylidene

• cleavage of the 4,6-O-benzylidene acetals using p-TsOH in MeOH under sonication followed by removal of the N-Troc groups in the presence of LiOH and subsequent acetylation with pyridine and acetic anhydride formed the desired acetamido functionalities, removal of the ester groups under basic conditions was

Raman spectroscopy as a tool for monitoring mesoscale continuous-flow organic synthesis: Equipment interface and assessment in four medicinally-relevant reactions

• Trevor A. Hamlin and
• Nicholas E. Leadbeater

Beilstein J. Org. Chem. 2013, 9, 1843–1852, doi:10.3762/bjoc.9.215

• )-ethyl 2-benzylidene-3-oxobutanoate (2a, 1.3095 g, 60%) as a clear yellow oil. 1H NMR (CDCl3, 400 MHz) δ ppm 1.26 (t, J = 7.21 Hz, 3H), 2.41 (s, 3H), 4.32 (q, J = 7.09 Hz, 2H), 7.33–7.41 (m, 3H), 7.42–7.47 (m, 2H), 7.56 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ ppm 14.08 (CH3), 26.74 (CH3), 61.92 (CH2), 129.06

• 1608 cm-1 vs concentration of 3-acetyl coumarin (1), yielding a straight line, y = mx + b; m = Raman intensity·M−1 of 1. Monitoring the conversion of benzaldehyde and ethyl acetoacetate to (Z)-ethyl 2-benzylidene-3-oxobutanoate (2a) across a range of reaction conditions (scan time = 15 s, integration

• )-one (4a) across a range of reaction conditions (scan time = 15 s, integration = 10 s). The reaction between salicylaldehyde and ethyl acetoacetate to form 3-acetyl coumarin (1). The Knoevenagel condensation of benzaldehyde and ethyl acetoacetate to yield (Z)-ethyl 2-benzylidene-3-oxobutanoate (2a

Straightforward synthesis of a tetrasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O16

• Manas Jana and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2013, 9, 1757–1762, doi:10.3762/bjoc.9.203

• -benzylidene-2-deoxy-α-D-glucopyranoside (6): Similar as described in [21]. To a solution of compounds 2 (2 g, 5.00 mmol) and 3 (2.5 g, 5.42 mmol) in anhydrous CH2Cl2 (10 mL) was added MS 4 Å (2 g), and the reaction mixture was stirred under an argon atmosphere at room temperature for 30 min. The reaction

• -Methoxyphenyl (6-O-acetyl-2,3,4-tri-O-benzyl-α-D-glucopyranosyl)-(1→3)-(2-O-acetyl-4-O-benzyl-α-L-rhamnopyranosyl)-(1→3)-2-azido-4,6-O-benzylidene-2-deoxy-α-D-glucopyranoside (7): Similar as described in [21]. To a solution of compounds 6 (2 g, 2.95 mmol) and 4 (1.7 g, 3.16 mmol) in anhydrous CH2Cl2/Et2O (10 mL

• ), 62.4 (C-6C), 55.5 (OCH3), 20.8, 20.7 (2 COCH3), 17.3 (CCH3); ESI–MS: 1174.4 [M + Na]+; Anal. calcd for C64H69N3O17: C, 66.71; H, 6.04%; found: C, 66.54; H, 6.20%. p-Methoxyphenyl (2,3,4-tri-O-benzyl-α-D-glucopyranosyl)-(1→3)-(4-O-benzyl-α-L-rhamnopyranosyl)-(1→3)-2-azido-4,6-O-benzylidene-2-deoxy-α-D

Short synthesis of the common trisaccharide core of kankanose and kankanoside isolated from Cistanche tubulosa

• Goutam Guchhait and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2013, 9, 705–709, doi:10.3762/bjoc.9.80

• the presence of borontrifluoride diethyl etherate furnished 2-phenylethyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside (2) in 84% yield [10]. Saponification of compound 2 by using 0.1 M sodium methoxide in methanol followed by benzylidene acetal formation by using benzaldehyde dimethylacetal in the

• = 7.5 Hz, H-1A in the 1H NMR and at δ 101.9 (PhCH), 101.3 (C-1A), 97.4 (C-1B) in the 13C NMR spectra]. Removal of the benzylidene acetal group under neutral conditions by using triethylsilane and Pd/C [15] resulted in the formation of disaccharide diol 7 in 80% yield. NOBF4 catalyzed regio- and

• solvents of adequate purity were used in all reactions. 2-Phenylethyl 4,6-O-benzylidene-β-D-glucopyranoside (5): A solution of compound 2 (5.0 g, 11.05 mmol) in 0.1 M CH3ONa in CH3OH (70 mL) was stirred at room temperature for 3 h and was neutralized with Amberlite IR-120 (H+) resin. The reaction mixture

New simple synthesis of ring-fused 4-alkyl-4H-3,1-benzothiazine-2-thiones: Direct formation from carbon disulfide and (E)-3-(2-aminoaryl)acrylates or (E)-3-(2-aminoaryl)acrylonitriles

• Qiuping Ding,
• Yuqing Lin,
• Guangni Ding,
• Fumin Liao,
• Xiaoyan Sang and
• Yi-Yuan Peng

Beilstein J. Org. Chem. 2013, 9, 460–466, doi:10.3762/bjoc.9.49

• of novel natural-product-like compounds [18][19][20][21][22], we recently reported the practical synthesis of 2-mercapto-4-benzylidene-4H-benzo[d][1,3]thiazines starting from 2-alkynylbenzenamines with CS2, and further transformations to highly functionalized 4-benzylidene-4H-benzo[d][1,3]thiazines

Removal of benzylidene acetal and benzyl ether in carbohydrate derivatives using triethylsilane and Pd/C

• Abhishek Santra,
• Tamashree Ghosh and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2013, 9, 74–78, doi:10.3762/bjoc.9.9

• Abhishek Santra Tamashree Ghosh Anup Kumar Misra Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata-700054, India; FAX: 91-33-2355 3886 10.3762/bjoc.9.9 Abstract Clean deprotection of carbohydrate derivatives containing benzylidene acetals and benzyl ethers was

• achieved under catalytic transfer hydrogenation conditions by using a combination of triethylsilane and 10% Pd/C in CH3OH at room temperature. A variety of carbohydrate diol derivatives were prepared from their benzylidene derivatives in excellent yield. Keywords: benzylidene; glycoside; Pd/C; transfer

• hydrogenation; triethylsilane; Introduction Functionalization of carbohydrate intermediates is essential for their assembly towards the synthesis of complex oligosaccharides [1][2][3][4][5][6][7][8][9]. Benzylidene acetal is a frequently used protecting group for the simultaneous protection of 1,2- and 1,3

A new family of four-ring bent-core nematic liquid crystals with highly polar transverse and end groups

• Kalpana Upadhyaya,
• Venkatesh Gude,
• Golam Mohiuddin and
• Rao V. S. Nandiraju

Beilstein J. Org. Chem. 2013, 9, 26–35, doi:10.3762/bjoc.9.4

• , while the central bent core possesses a chloro substituent projected at a location inside the molecular core to represent the transverse dipole. The other end of the molecule is linked to 4-n-alkoxysalicylaldehyde through an imine moiety, which actually seems superior to the benzylidene aniline core and

• molecules overlap. This contributes to the strong attractive interaction between them. The molecule consists of two linkages between the three aromatic fragments, giving an ortho-hydroxy benzylidene moiety, a benzoic acid ester moiety, and a biphenyl residue. The salicylidene linkage instead of the

• unsubstituted benzylidene linkage was preferred due to the presence of the ortho-hydroxy group, which enhances the transverse dipole moment as well as the stability of the imines through intramolecular H-bonding to overcome the hydrolytic instability of the molecules towards moisture. The bent-core platform was

Asymmetric synthesis of γ-chloro-α,β-diamino- and β,γ-aziridino-α-aminoacylpyrrolidines and -piperidines via stereoselective Mannich-type additions of N-(diphenylmethylene)glycinamides across α-chloro-N-sulfinylimines

• Gert Callebaut,
• Sven Mangelinckx,
• Pieter Van der Veken,
• Karl W. Törnroos,
• Koen Augustyns and
• Norbert De Kimpe

Beilstein J. Org. Chem. 2012, 8, 2124–2131, doi:10.3762/bjoc.8.239

• , comparable non-halogenated trans-imidazolidines were already synthesized by 1,3-dipolar cycloaddition of N-benzylidene glycine ester enolates across N-sulfinylaldimines in the presence of a Lewis acid [43]. The trans-stereochemistry of imidazolidine 12b was ensured by the vicinal coupling constant 3JH4-H5

Convergent synthesis of the tetrasaccharide repeating unit of the cell wall lipopolysaccharide of Escherichia coli O40

• Abhijit Sau and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2012, 8, 2053–2059, doi:10.3762/bjoc.8.230

• ]; and (f) preparation of β-D-mannosidic moiety from the β-D-glucoside [13]. Benzylation of 2-azidoethyl 3-O-benzyl-4,6-O-benzylidene-β-D-mannopyranoside (2) [13] (prepared from D-glucose in nine steps) by using benzyl bromide and sodium hydroxide [21] followed by reductive ring opening of the 4,6-O

• -benzylidene acetal with triethylsilane and iodine [22] furnished compound 6 in 82% yield. Stereoselective glycosylation of compound 6 with thioglycoside derivative 3 in the presence of a combination of N-iodosuccinimide (NIS) and HClO4–SiO2 [17] gave disaccharide derivative 7 in a 77% yield. Formation of

• isopropylidene ketal and benzylidene acetal by acid hydrolysis; and finally (d) removal of benzyl ethers by using triethylsilane and 20% Pd(OH)2–C [20] to furnish target compound 1, which was purified through a Sephadex® LH-20 column to give pure compound 1 in 60% overall yield. Spectral data of compound 1

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers

• Ryszard Lazny,
• Aneta Nodzewska,
• Katarzyna Sidorowicz and
• Przemyslaw Kalicki

Beilstein J. Org. Chem. 2012, 8, 1877–1883, doi:10.3762/bjoc.8.216

• benzaldehyde or elimination to benzylidene derivatives. The behavior of the new isomer under the same isomerization conditions was similar and gave no indications regarding its stereochemical form. It appeared that in this case (as it was for the exo,anti isomer [3]) attempts to convert the presumed exo

• atom at the α-carbon to carbonyl (C-2) is likely responsible for the facile elimination of a water molecule and formation of an isomeric mixture of condensation products ((E) and (Z)-2-benzylidene tropinones) in analogy to the known elimination of acetic acid from the acetyl derivative of the aldol [3

Synthesis and ring openings of cinnamate-derived N-unfunctionalised aziridines

• Alan Armstrong and
• Alexandra Ferguson

Beilstein J. Org. Chem. 2012, 8, 1747–1752, doi:10.3762/bjoc.8.199

• found to be specific for tert-butyl esters, with γ- and δ-benzylidene lactones, methyl, ethyl, phenyl, and benzyl cinnamates all suffering from degradation, presumably via hydrolysis pathways. β-Alkyl-substituted enoates were not explored, and will be the subject of future investigation. A preliminary

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• -position of the phenyl ring of the benzylidene moiety, while the enantioselectivity of the reaction decreased if the phenyl ring was substituted with an electron-withdrawing group. The best result, with yields up to 96% and enantioselectivities up to 96%, was obtained in DCM solvent at −40 °C. An

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• –200 kJ mol–1) Lewis bases. While structurally analogous imidazolylidenes and imidazolidinylidenes have comparable nucleophilicities and Lewis basicities, the corresponding deoxy Breslow intermediates differ dramatically in reactivity. The thousand-fold higher nucleophilicity of 2-benzylidene

• -imidazoline relative to 2-benzylidene-imidazolidine is explained by the gain of aromaticity during electrophilic additions to the imidazoline derivatives. O-Methylated Breslow intermediates are a hundred-fold less nucleophilic than deoxy Breslow intermediates. Keywords: enamine activation; iminium activation

• deoxy Breslow intermediates 45a–f can be described by Equation 1 [107]. In contrast to the situation described for the NHCs in Figure 23, the benzylidene-imidazolines 45a,d are now 103 times more nucleophilic than the corresponding benzylidene-imidazolidines 45c,f (Figure 24 and Figure 25a). The

Organocatalytic C–H activation reactions

• Subhas Chandra Pan

Beilstein J. Org. Chem. 2012, 8, 1374–1384, doi:10.3762/bjoc.8.159

• regenerated (Scheme 11). The following year, Akiyama and co-workers reported another organocatalytic asymmetric synthesis of tetrahydroquinolines using chiral phosphoric acid as the catalyst [25]. In this instance, benzylidene malonates were used as the hydride acceptor. Another important feature of this

Studies on the substrate specificity of a GDP-mannose pyrophosphorylase from Salmonella enterica

• Lu Zou,
• Ruixiang Blake Zheng and
• Todd L. Lowary

Beilstein J. Org. Chem. 2012, 8, 1219–1226, doi:10.3762/bjoc.8.136

• . Results and Discussion Synthesis of 2-methoxy derivative 9 The synthesis of sugar 1-phosphate 9 containing a methyl group at O-2 commenced from 3-O-benzyl-4,6-O-benzylidene-α-D-mannopyranoside 14 [26] as illustrated in Scheme 1. Methylation of the alcohol under standard conditions proceeded in 80% yield

• affording 15. The benzylidene protecting group was cleaved, together with the methyl glycoside, by acetolysis giving the tetra-O-acetylated compound 16 in 81% yield. This glycosyl acetate was converted to the corresponding thioglycoside (17), which was, in turn, coupled with dibenzyl phosphate under NIS

• -benzylidene-α-D-mannopyranoside (19) [26] was first methylated giving 20 and then converted into glycosyl acetate 21 in 49% yield over the two steps. Subsequent thioglycosylation provided a 52% yield of 22. The protected dibenzyl phosphate 23 was next formed by the NIS–AgOTf promoted glycosylation of dibenzyl

Synthesis of 4” manipulated Lewis X trisaccharide analogues

• Christopher J. Moore and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2012, 8, 1134–1143, doi:10.3762/bjoc.8.126

• 12 [56] and 13 [12] (Figure 2). Synthesis of monosaccharide building blocks 8–11 Glucosamine acceptor 8 was prepared in two steps from the known [14] benzylidene 7: the benzylidene acetal was first hydrolyzed, and then the resulting diol (79%) was selectively benzoylated at O-6 (BzCl-collidine

Synthesis of fluorinated maltose derivatives for monitoring protein interaction by ¹⁹F NMR

• Michaela Braitsch,
• Hanspeter Kählig,
• Georg Kontaxis,
• Michael Fischer,
• Toshinari Kawada,
• Robert Konrat and
• Walther Schmid

Beilstein J. Org. Chem. 2012, 8, 448–455, doi:10.3762/bjoc.8.51

• regioselective reductive ring opening of benzylidene acetals in the maltose derivative 11 was performed with a complex of BH3/Bu2BOTf at −70 °C [32][33]. Fluorination with DAST [34][35] was performed in a sealed tube for 1 h at 80 °C under microwave conditions. The deprotection of the benzyl group was achieved

• with Pd/C [36], followed by a Zemplén saponification to obtain product 15. Starting from 4′,6′-O-benzylidene maltose 10 [37], the primary alcohol was protected as tert-butyldimethylsilyl ether followed by standard peracetylation (Scheme 2). Treatment of the silyl protecting group with an excess of

• Deoxofluor [38] yielded the 6-F-maltose derivatives 18. Final deprotection with acetic acid [37][39] and sodium methoxide yielded compound 20. The synthesis of the galacto-type derivative 23 started from peracetylated benzylidene maltose 11 [37]. Deprotection [37] with acetic acid followed by microwave

Facile synthesis of nitrophenyl 2-acetamido-2-deoxy-α-D-mannopyranosides from ManNAc-oxazoline

• Karel Křenek,
• Petr Šimon,
• Lenka Weignerová,
• Barbora Fliedrová,
• Marek Kuzma and
• Vladimír Křen

Beilstein J. Org. Chem. 2012, 8, 428–432, doi:10.3762/bjoc.8.48

• % yield) or from methyl 4,6-O-benzylidene-α-D-glucopyranoside (5 steps, 23%). Unfortunately, in our hands this synthetic procedure did not afford the published yields, namely in the triflate and consequent azide substitution steps. Oxazolines, such as 3, have been used as glycosylation agents in the

Acceptor-influenced and donor-tuned base-promoted glycosylation

• Stephan Boettcher,
• Martin Matwiejuk and
• Joachim Thiem

Beilstein J. Org. Chem. 2012, 8, 413–420, doi:10.3762/bjoc.8.46

• glucopyranosyl acceptors 1–4 started with benzylidenation [4] of compound 10 and 11, respectively (Scheme 1). As the next step, monobenzylation of 12 and 13 by phase-transfer catalysis [5] afforded derivatives 14–17. Subsequent cleavage of the benzylidene protecting group [4] gave the target compounds 1–4 in

• -glycopyranoside acceptor 6 started with benzylidenation [4] of 19, followed by monobenzylation via intermediate stannylidene acetal formation [6] and subsequent cleavage of the benzylidene group [4]. Formation of the perbenzylated α-fucopyranosyl chloride was achieved according to [2]. Starting with peracetylated

Synthesis and mesomorphic properties of calamitic malonates and cyanoacetates tethered to 4-cyanobiphenyls

• Katharina C. Kress,
• Martin Kaller,
• Kirill V. Axenov,
• Stefan Tussetschläger and
• Sabine Laschat

Beilstein J. Org. Chem. 2012, 8, 371–378, doi:10.3762/bjoc.8.40

• malonates and cyanoacetates are well known as suitable ligands for strong coordination of main-group and transition metals [25]. Benzylidene derivatives of malonic esters, so called swallow-tailed liquid crystals, were described as forming smectic phases [26]. However, most work on liquid-crystalline

Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

• Sonja Findeisen-Tandel,
• Wolfgang Weissflog,
• Ute Baumeister,
• Gerhard Pelzl,
• H. N. Shreenivasa Murthy and
• Channabasaveshwar V. Yelamaggad

Beilstein J. Org. Chem. 2012, 8, 129–154, doi:10.3762/bjoc.8.15

• the benzylidene derivative H 3a. The introduction of the hydroxy groups enables the salicylideneaniline compound OH 3a to form a mesophase. The clearing temperature of the bromine-substituted compound OH 3b increases due to the presence of hydroxy groups, in comparison to H 3b, by 34 K. Liquid

Dependency of the regio- and stereoselectivity of intramolecular, ring-closing glycosylations upon the ring size

• Patrick Claude,
• Christian Lehmann and
• Thomas Ziegler

Beilstein J. Org. Chem. 2011, 7, 1609–1619, doi:10.3762/bjoc.7.189

• -O-benzyl-2-O-(3-carboxypropionyl)-1-thio-β-D-galactopyranoside (1) was condensed via its pentafluorophenyl ester 2 with 5-aminopentyl (4a), 4-aminobutyl (4b), 3-aminopropyl (4c) and 2-aminoethyl 4,6-O-benzylidene-β-D-glucopyranoside (4d), prepared from the corresponding N-Cbz protected glucosides 3a

• in ratios depending upon the ring size formed during glycosylation. No β(1→2) linked disaccharides were formed. Molecular modeling of saccharides 6–8 revealed that a strong aromatic stacking interaction between the aromatic parts of the benzyl and benzylidene protecting groups in the galactosyl and

• 1-thio-galactosyl donor and a 4,6-O-benzylidene-glucose acceptor tethered by peptide-bond-containing linkers of variable size, in order to study systematically the parameters influencing the outcome of the intramolecular, ring-closing glycosylation step. In order to further provide a rationalization

Convergent synthesis of the tetrasaccharide repeating unit of the O-antigen of Shigella boydii type 9

• Abhishek Santra and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2011, 7, 1182–1188, doi:10.3762/bjoc.7.137

• recently developed environmentally benign reaction conditions for protecting group manipulations and glycosylations such as, (i) O-acetylation using sulfamic acid [20], (ii) regioselective ring opening of the benzylidene acetal using a combination of triethylsilane and iodine [21], (iii) direct one-pot

• , 3, 4 and 7 were prepared from commercially available reducing mono- and disaccharides utilizing a series of reaction methodologies reported earlier. 4-Methoxyphenyl (4,6-O-benzylidene-α-D-glucopyranosyl)-(1→4)-β-D-glucopyranoside (5) [32] was subjected to a sequence of reactions involving

• acetylation using acetic anhydride in the presence of sulfamic acid [20] followed by regioselective reductive ring opening of the benzylidene acetal using a combination of triethylsilane and iodine [21] to furnish 4-methoxyphenyl (2,3-di-O-acetyl-6-O-benzyl-α-D-glucopyranosyl)-(1→4)-2,3,6-tri-O-acetyl-β-D

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• a 6-endo-dig cyclization to give 4H-pyrans 82. By contrast, alkylidene/benzylidene-substituted tetrahydrofuranyl ethers 80 are formed in a tandem nucleophilic addition/cycloisomerization in alcoholic solvents [44]. Similarly, Belot et al. reported a gold-catalyzed cyclization which led to nitro

• arylidene group transfer were developed as a method for the preparation of 4-arylidene isoxazol-5(4H)-ones [62]. For example, (E)-benzaldehyde O-3-phenylpropioloyl oxime 132 was reacted in acetonitrile at 25 °C in the presence of AuPPh3NTf2 (5 mol %) to give 4-benzylidene-3-phenylisoxazol-5(4H)-one 133 in

Synthesis, reactivity and biological activity of 5-alkoxymethyluracil analogues

• Lucie Brulikova and
• Jan Hlavac

Beilstein J. Org. Chem. 2011, 7, 678–698, doi:10.3762/bjoc.7.80

• studies on the synthesis of pseudouridine (Scheme 29) [47]. Thus, 2,4-di-tert-butoxypyrimidin-5-yllithium (170) was reacted with 2,4:3,5-di-O-benzylidene-aldehydo-D-ribose (171) in tetrahydrofuran to afford a mixture of allo and altro isomers of 5-(2,4:3,5-di-O-benzylidene-D-pentahydroxypentyl)-2,4-di

• ). Synthesis of “metallocenonucleosides” 164 and 167. Synthesis of 5-(2,4:3,5-di-O-benzylidene-D-pentahydroxypentyl)-2,4-di-tert-butoxy-pyrimidine 172 and 173. Acknowledgements The authors are grateful to the Ministry of Education, Youth and Sport of the Czech Republic, for the grant MSM6198959216 and for