High Dose Ascorbic Acid w/ Melphalan

This is a single arm Phase I trial evaluating safety, tolerability, and efficacy of High Dose Ascorbic Acid (HDAA) in patients with plasma cell disorders. This is a single arm study. Subjects will receive a test dose of HDAA alone at screening (15gm), then proceed to either 75, 100, or 125 gm, depending upon the cohort) on day -4, HDAA combined with melphalan 100 mg/m2 on day -1, and ASCT on day 0. Four additional HDAA doses (each of which is either 75, 100, or 125 gm, depending upon the cohort) will then be administered 3 days apart on D+2, D+5, D+8 and D+11, followed by weekly doses of the corresponding dose of HDAA for four additional weeks.Lab tests, vitals, and scans will be performed to assess tolerability, safety, and efficacy at each scheduled infusion timepoint.