Part I: Synthesis of Cyclobutyl Nucleoside and NucleotideAnalogues as HIV-1 Reverse Transcriptase InhibitorsPart II: Improvement of Glycosylation Regioselectivity in PurineNucleoside Analogue SynthesisPart III: Enantioselective Synthesis ofβ-D-Dioxolane-T andβ-D-FDOC