Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Kuijpers, W. H. A., Genderen, van, M. H. P., ... Buck, H. M. (1989). Synthesis of phosphate-methylated DNA fragments using 9-fluorenylmethoxycarbonyl as transient base protecting group. Journal of Organic Chemistry, 54(7), 1657-1664. DOI: 10.1021/jo00268a030 Link to publication Citation for published version (APA):General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Download date: 11. May. 2018 J. Org. Chem. 1989Chem. ,54, 1657Chem. -1664 1657Merck silica gel, 230-400 mesh, was used for flash chromatography, and Whatman Magnum-9 Partisil-10 and ODs-3 columns were used for preparative HPLC.Isolation and Extraction. Fresh leaves of C. dichogamus were collected in Kenya in mid-1987 (a voucher sample has been deposited a t the herbarium in the Botany Dept., UBC). The airdried leaves (225 g) were soaked in methanol (500 mL) overnight. The methanol extract was concentrated in vacuo to a gum, water was added, and the resulting suspension was exhaustively extracted with CH2C12. Evaporation of the combined organic extracts in vacuo gave a residue, which was fractionated via silica gel flash chromatography (step gradient: CH2C12 to EtOAc) to give crude crotoxides A (1) and B (2).Crotoxide A (1). The flash fractions containing crude crotoxide A (1) were combined and further purified by silica gel preparative TLC (2:l CH2C12/EtOAc). The preparative TLC fraction containing crotoxide A was dissolved in methanol (5 mL), palladium on charcoal was added (20 mg), and the suspension was stirred at room temperature under 1 atm of hydrogen for 2 days. Filtration of t...

It has been shown that the phosphate-methylated DNA dinucleotides d(CpC) (1) and d(TpC) (2) form a parallel miniduplex exclusively for the S configuration on phosphorus, which corresponds with outward orientation of the methyl group from the helix into the solvent. The melting temperatures (T, values) of the parallel duplexes of (Sp)-l and (Sp)-2 are 33 "C and 26 "C, respectively. The phosphate-sugar backbone strands adopt a standard right-handed geometry. The imino resonances in the 600-MHz 'H NMR spectra strongly point at C C base pairing via two symmetry-related NH,--N hydrogen bonds, as was also observed in the X-ray crystal structure of 2'-deoxycytidine. From our previous work, it is known that phosphate-methylated d(TpT) forms parallel miniduplexes with an equal stability for the Sp and R p diastereoisomers. Therefore, it is concluded that the RP configuration (which is associated with location of the methyl group inside the helix groove) is unfavorable in the case of C-C base pairing. This conclusion was corroborated by AMBER molecular mechanics calculations, which showed that the larger propeller twist angle for C-C base pairing (-41"), in comparison with T-T base pairing (=25"), results in narrowing of the helix groove.

DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

The proposed activated state of cyclic adenosine 3 ',