David T. Mao

University Center Rochester, Rochester, Minnesota, United States

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Publications (5)23.85 Total impact

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    ABSTRACT: Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193) is a C-glycosyl thiazole nucleoside with antitumor activity. Crystal structures of tiazofurin and its alpha,2'-deoxy and xylo analogues all show close contacts between the thiazole sulfur (S) and the furanose ring oxygen (O1'). These contacts have been interpreted in terms of an attractive intramolecular S-O interaction in the thiazole nucleosides. Ara-tiazofurin (2-beta-D-arabinofuranosylthiazole-4-carboxamide, ara-T) is the inactive arabinose analogue of tiazofurin. The crystal structure of ara-T is reported. This structure provides evidence for an attractive S-O interaction not seen in the other thiazole nucleosides. The conformation about the C-glycosyl bond in ara-T is such that close contacts are formed between the thiazole sulfur and both O1' and the 2'-hydroxyl oxygen O2'. This conformation is interpreted in terms of an additional attractive interaction between S and O2'. This interpretation is supported by comparison of the conformation of ara-T with those of other ara-nucleosides. These findings provide further evidence for an attractive S-O interaction in the thiazole nucleosides. Ara-T also demonstrates a second conformational feature found in these compounds: the carboxamide nitrogen remains cis to the thiazole nitrogen. Implications of these potentially constrained conformational features are discussed in terms of the mechanism of activity of tiazofurin.
    Journal of Medicinal Chemistry 06/1988; 31(5):1026-31. DOI:10.1021/jm00400a024 · 5.48 Impact Factor
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    ABSTRACT: One of the problems encountered in the use of tetrahydrouridine (THU, 2) and saturated 2-oxo-1,3-diazepine nucleosides as orally administered cytidine deaminase (CDA) inhibitors is their acid instability. Under acid conditions these compounds are rapidly converted into inactive ribopyranoside forms. A solution this problem was sought by functionalizing the acid-stable but less potent CDA inhibitor 1-beta-D-ribofuranosyl-2(1H)-pyrimidinone (1) with the hope of increasing its potency to the level achieved with THU. The selection of the hydroxymethyl substituent at C-4, which led to the synthesis of 4-(hydroxymethyl)-1-beta-D-ribofuranosyl-2(1H)-pyrimidinone (10), 3,4-dihydro-4-(hydroxymethyl)-1-beta-D-ribofuranosyl-2(1H)-pyrimidinone (7), and 3,4,5,6-tetrahydro-4-(dihydroxymethyl)-1-beta-D-ribofuranosyl-2(1H)-p yrimidinone (28) was based on the transition-state (TS) concept. The key intermediate precursor, 4-[(benzoyloxy)methyl]-1-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)-2(H) -pyrimidinone (24), was obtained via the classical Hilbert-Johnson reaction between 2-methoxy-4-[(benzoyloxy)methyl]pyrimidine (20) and 2,3,5-tri-O-benzoyl-1-D-ribofuranosyl bromide (21). Deprotection of 24 afforded compound 10, while its sodium borohydride reduction products afforded compounds 7 and 28 after removal of the blocking groups. Syntheses of 3,4-dihydro-1-beta-D-ribofuranosyl-2(1H)-pyrimidinone (9) and 3,6-dihydro-1-beta-D-ribofuranosyl-2(1H)-pyrimidinone (8), which lack the hydroxymethyl substituent, was accomplished in a similar fashion. The new compounds bearing the hydroxymethyl substituent were more acid stable than THU, and their CDA inhibitory potency, expressed in terms of Ki values, spanned from 10(-4) to 10(-7) M in a manner consistent with the TS theory. Compound 7, in particular, was superior to its parent 1 and equipotent to THU (Ki = 4 X 10(-7) M) when examined against mouse kidney CDA. The superior acid stability of this compound coupled to its potent inhibitory properties against CDA should provide a means of testing oral combinations of rapidly deaminated drugs, viz. ara-C, without the complications associated with the acid instability of THU.
    Journal of Medicinal Chemistry 09/1986; 29(8):1374-80. DOI:10.1021/jm00158a009 · 5.48 Impact Factor
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    ABSTRACT: Tiazofurin (TR), a new antitumor agent, enters human erythrocytes by utilizing their facilitated nucleoside transport system. TR competes with endogenous nucleosides for this transport mechanism, thereby reducing nucleoside uptake into the cells. Pre-incubation of erythrocytes for 10 min at 22 degrees C with 100 microM and 500 microM TR reduced the transport of 14C-uridine into the cells by 27% and 74%, respectively. Simultaneous exposure of cells to TR and [14C]uridine did not alter the inhibitory effect of TR. Furthermore, the transport inhibitory effect of TR was lost when cells were washed twice with Hanks basal salt solution following a 10-min pre-incubation with TR. The Km and Vmax (+/- S.E.) for radiolabeled TR transport into erythrocytes are 170 +/- 26 microM and 55 +/- 13 nmol/h per 10(6) cells, respectively, which is similar to the kinetic constants measured for uridine transport into erythrocytes (Km = 168 +/- 37 microM and Vmax = 61 +/- 16 nmol/h per 10(6) cells). The Ki (+/- S.E.) of TR for uridine transport is 178 +/- 11 microM and for thymidine transport is 102 +/- 59 microM. Three analogues of TR (its selenium isostere (SR), and Ara (Ara-TR) and Xylo (Xylo-TR) derivatives) were compared with TR for their ability to compete with and inhibit uridine transport, as these analogues were not available in a radiolabeled form for direct measurement of their transport into the cell. SR had similar kinetic characteristics of inhibition of uridine transport to TR (Ki = 145 +/- 15 microM) but Ara-TR had a Ki = 1.04 +/- 0.13 mM while Xylo-TR inhibited uridine transport with a Ki = 1.57 +/- 0.67 mM. Thus, TR is transported into erythrocytes with the same velocity and affinity for the carrier as uridine and competitively inhibits nucleoside transport into the cell. Of 3 other C-nucleoside derivatives examined, SR is of similar potency to TR but Ara-TR and Xylo-TR are much less effective at competing with uridine for the nucleoside transporter.
    Cancer Letters 09/1985; 28(1):1-8. DOI:10.1016/0304-3835(85)90085-0 · 5.02 Impact Factor
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    ABSTRACT: The ribo- and arabinofuranosyl nucleosides of antitumor active 2- and 4-pyridones 1a and 2a were prepared by direct condensation of the silylated bases with either 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose (4a) or 2,3,5-tri-O-benzyl-1-p-nitrobenzoyl-D-arabinofuranose (7) in the presence of trimethylsilyl triflate (Me3SiOTf). In the case of the arabinofuranosyl nucleosides, separation of the alpha and beta anomers was accomplished at the stage of O-benzyl-protected compounds (8b + 9b, and 10b + 11b) after chemical functionalization of the 3-hydroxy group of the pyridone aglycons with acetyl and benzyl groups, respectively. Deblocking of the protected ribo- and arabinofuranosyl nucleosides was performed by the standard methods. In vitro activity against P-388 cells in culture indicated that the 4-pyridone riboside 6d was the most active member of the series with a twofold lower ID50 than the parent pyridone 2a. However, this and all the other compounds tested in this series showed no activity against the in vivo model system of murine P-388 leukemia at doses ranging from 25 to 400 mg/kg qd 1-5.
    Journal of Medicinal Chemistry 03/1984; 27(2):160-4. DOI:10.1021/jm00368a010 · 5.48 Impact Factor
  • David T. Mao, Victor E. Marquez
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    ABSTRACT: The syntheses of the heretofore unknown 2-β-D-ara and 2-β-D-xylofuranosyl isomers of the antitumor agent tiazofurin have been accomplished. In both cases the stereospecific inversion of the required 2′ or 3′-hydroxyl group in the protected parent compound afforded the desired products.
    Tetrahedron Letters 01/1984; 25(20):2111–2114. DOI:10.1016/S0040-4039(01)81174-6 · 2.39 Impact Factor

Publication Stats

108 Citations
23.85 Total Impact Points

Institutions

  • 1988
    • University Center Rochester
      • Department of Biophysics
      Rochester, Minnesota, United States
  • 1984–1985
    • National Institutes of Health
      • • Program of Developmental Therapeutics
      • • Chemical Biology Laboratory
      Maryland, United States
    • NCI-Frederick
      Фредерик, Maryland, United States